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1
Shima, Seigo, Gangfeng Huang, Tristan Wagner, and Ulrich Ermler. "Structural Basis of Hydrogenotrophic Methanogenesis." Annual Review of Microbiology 74, no. 1 (September 8, 2020): 713–33. http://dx.doi.org/10.1146/annurev-micro-011720-122807.
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Most methanogenic archaea use the rudimentary hydrogenotrophic pathway—from CO2 and H2 to methane—as the terminal step of microbial biomass degradation in anoxic habitats. The barely exergonic process that just conserves sufficient energy for a modest lifestyle involves chemically challenging reactions catalyzed by complex enzyme machineries with unique metal-containing cofactors. The basic strategy of the methanogenic energy metabolism is to covalently bind C1 species to the C1 carriers methanofuran, tetrahydromethanopterin, and coenzyme M at different oxidation states. The four reduction reactions from CO2 to methane involve one molybdopterin-based two-electron reduction, two coenzyme F420–based hydride transfers, and one coenzyme F430–based radical process. For energy conservation, one ion-gradient-forming methyl transfer reaction is sufficient, albeit supported by a sophisticated energy-coupling process termed flavin-based electron bifurcation for driving the endergonic CO2 reduction and fixation. Here, we review the knowledge about the structure-based catalytic mechanism of each enzyme of hydrogenotrophic methanogenesis.
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Lie, Thomas J., Kyle C. Costa, Boguslaw Lupa, Suresh Korpole, William B. Whitman, and John A. Leigh. "Essential anaplerotic role for the energy-converting hydrogenase Eha in hydrogenotrophic methanogenesis." Proceedings of the National Academy of Sciences 109, no. 38 (August 7, 2012): 15473–78. http://dx.doi.org/10.1073/pnas.1208779109.
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Despite decades of study, electron flow and energy conservation in methanogenic Archaea are still not thoroughly understood. For methanogens without cytochromes, flavin-based electron bifurcation has been proposed as an essential energy-conserving mechanism that couples exergonic and endergonic reactions of methanogenesis. However, an alternative hypothesis posits that the energy-converting hydrogenase Eha provides a chemiosmosis-driven electron input to the endergonic reaction. In vivo evidence for both hypotheses is incomplete. By genetically eliminating all nonessential pathways of H2 metabolism in the model methanogen Methanococcus maripaludis and using formate as an additional electron donor, we isolate electron flow for methanogenesis from flux through Eha. We find that Eha does not function stoichiometrically for methanogenesis, implying that electron bifurcation must operate in vivo. We show that Eha is nevertheless essential, and a substoichiometric requirement for H2 suggests that its role is anaplerotic. Indeed, H2 via Eha stimulates methanogenesis from formate when intermediates are not otherwise replenished. These results fit the model for electron bifurcation, which renders the methanogenic pathway cyclic, and as such requires the replenishment of intermediates. Defining a role for Eha and verifying electron bifurcation provide a complete model of methanogenesis where all necessary electron inputs are accounted for.
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Hao, L. P., L. Mazéas, F. Lü, J. Grossin-Debattista, P. J. He, and T. Bouchez. "Effect of ammonia on methane production pathways and reaction rates in acetate-fed biogas processes." Water Science and Technology 75, no. 8 (February 3, 2017): 1839–48. http://dx.doi.org/10.2166/wst.2017.032.
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In order to understand the correlation between ammonia and methanogenesis metabolism, methane production pathways and their specific rates were studied at total ammonium nitrogen (TAN) concentrations of 0.14–9 g/L in three methanogenic sludges fed with acetate, at both mesophilic and thermophilic conditions. Results showed that high levels of TAN had significant inhibition on methanogenesis; this could, however, be recovered via syntrophic acetate oxidation (SAO) coupled with Hydrogenotrophic Methanogenesis (HM) performed by acetate oxidizing syntrophs or through Acetoclastic Methanogenesis (AM) catalyzed by Methanosarcinaceae, after a long lag phase >50 d. Free ammonia (NH3) was the active component for this inhibition, of which 200 mg/L is suggested as the threshold for the pathway shift from AM to SAO-HM. Methane production rate via SAO-HM at TAN of 7–9 g/L was about 5–9-fold lower than that of AM at TAN of 0.14 g/L, which was also lower than the rate of AM pathway recovered at TAN of 7 g/L in the incubations with a French mesophilic inoculum. Thermophilic condition favored the establishment of the SAO-catalyzing microbial community, as indicated by the higher reaction rate and shorter lag phase. The operational strategy is thus suggested to be adjusted when NH3 exceeds 200 mg/L.
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Richards, Matthew A., Thomas J. Lie, Juan Zhang, Stephen W. Ragsdale, John A. Leigh, and Nathan D. Price. "Exploring Hydrogenotrophic Methanogenesis: a Genome Scale Metabolic Reconstruction of Methanococcus maripaludis." Journal of Bacteriology 198, no. 24 (October 10, 2016): 3379–90. http://dx.doi.org/10.1128/jb.00571-16.
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ABSTRACTHydrogenotrophic methanogenesis occurs in multiple environments, ranging from the intestinal tracts of animals to anaerobic sediments and hot springs. Energy conservation in hydrogenotrophic methanogens was long a mystery; only within the last decade was it reported that net energy conservation for growth depends on electron bifurcation. In this work, we focus onMethanococcus maripaludis, a well-studied hydrogenotrophic marine methanogen. To better understand hydrogenotrophic methanogenesis and compare it with methylotrophic methanogenesis that utilizes oxidative phosphorylation rather than electron bifurcation, we have built iMR539, a genome scale metabolic reconstruction that accounts for 539 of the 1,722 protein-coding genes ofM. maripaludisstrain S2. Our reconstructed metabolic network uses recent literature to not only represent the central electron bifurcation reaction but also incorporate vital biosynthesis and assimilation pathways, including unique cofactor and coenzyme syntheses. We show that our model accurately predicts experimental growth and gene knockout data, with 93% accuracy and a Matthews correlation coefficient of 0.78. Furthermore, we use our metabolic network reconstruction to probe the implications of electron bifurcation by showing its essentiality, as well as investigating the infeasibility of aceticlastic methanogenesis in the network. Additionally, we demonstrate a method of applying thermodynamic constraints to a metabolic model to quickly estimate overall free-energy changes between what comes in and out of the cell. Finally, we describe a novel reconstruction-specific computational toolbox we created to improve usability. Together, our results provide a computational network for exploring hydrogenotrophic methanogenesis and confirm the importance of electron bifurcation in this process.IMPORTANCEUnderstanding and applying hydrogenotrophic methanogenesis is a promising avenue for developing new bioenergy technologies around methane gas. Although a significant portion of biological methane is generated through this environmentally ubiquitous pathway, existing methanogen models portray the more traditional energy conservation mechanisms that are found in other methanogens. We have constructed a genome scale metabolic network ofMethanococcus maripaludisthat explicitly accounts for all major reactions involved in hydrogenotrophic methanogenesis. Our reconstruction demonstrates the importance of electron bifurcation in central metabolism, providing both a window into hydrogenotrophic methanogenesis and a hypothesis-generating platform to fuel metabolic engineering efforts.
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Kim, In S., Henry H. Tabak, and James C. Young. "Modeling of the fate and effect of chlorinated phenols in anaerobic treatment processes." Water Science and Technology 36, no. 6-7 (September 1, 1997): 287–94. http://dx.doi.org/10.2166/wst.1997.0602.
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Studies were conducted to assess the biotransformation kinetics and inhibitory effects of mono-, di-, and trichlorophenol on acetogenic and methanogenic reactions using a standardized anaerobic protocol (Young and Tabak, 1993). Intrinsic kinetic parameters were estimated for each reaction using the Monod model. Reductive dechlorination of the toxicants was investigated using acclimated mixed cultures under methanogenic conditions. The studies indicated that inhibition of acetogenesis and methanogenesis was best described using exponential rather than linear inhibition terms. A second significant observation was that acclimated test cultures had a finite biodegradation capacity for each chemical that was related to the mass of microorganism present. A unique feature of the test program was that inhibition and biodegradation were modeled using the specific biomass responsible for acetogenesis and methanogenesis rather than the total anaerobic biomass.
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Staley, Bryan F., Francis L. de los Reyes, and Morton A. Barlaz. "Effect of Spatial Differences in Microbial Activity, pH, and Substrate Levels on Methanogenesis Initiation in Refuse." Applied and Environmental Microbiology 77, no. 7 (February 4, 2011): 2381–91. http://dx.doi.org/10.1128/aem.02349-10.
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ABSTRACTThe initiation of methanogenesis in refuse occurs under high volatile fatty acid (VFA) concentration and low pH (5.5 to 6.25), which generally are reported to inhibit methanogenicArchaea. One hypothesized mechanism for the initiation of methanogenesis in refuse decomposition is the presence of pH-neutral niches within the refuse that act as methanogenesis initiation centers. To provide experimental support for this mechanism, laboratory-scale landfill reactors were operated and destructively sampled when methanogenesis initiation was observed. The active bacterial and archaeal populations were evaluated using RNA clone libraries, RNA terminal restriction fragment length polymorphism (T-RFLP), and reverse transcription-quantitative PCR (RT-qPCR). Measurements from 81 core samples from vertical and horizontal sections of each reactor showed large spatial differences in refuse pH, moisture content, and VFA concentrations. No pH-neutral niches were observed prior to methanogenesis. RNA clone library results showed that active bacterial populations belonged mostly toClostridiales, and that methanogenicArchaeaactivity at low pH was attributable toMethanosarcina barkeri. After methanogenesis began, pH-neutral conditions developed in high-moisture-content areas containing substantial populations ofM. barkeri. These areas expanded with increasing methane production, forming a reaction front that advanced to low-pH areas. Despite low-pH conditions in >50% of the samples within the reactors, the leachate pH was neutral, indicating that it is not an accurate indicator of landfill microbial conditions. In the absence of pH-neutral niches, this study suggests that methanogens tolerant to low pH, such asM. barkeri, are required to overcome the low-pH, high-VFA conditions present during the anaerobic acid phase of refuse decomposition.
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Nozhevnikova, Alla N., C. Holliger, A. Ammann, and A. J. B. Zehnder. "Methanogenesis in sediments from deep lakes at different temperatures (2–70°C)." Water Science and Technology 36, no. 6-7 (September 1, 1997): 57–64. http://dx.doi.org/10.2166/wst.1997.0575.
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Methanogenic degradation of organic matter occurs in a wide temperature range from psychrophilic to extreme thermophilic conditions. Mesophilic and thermophilic methanogenesis is relatively well investigated, but little is known about low temperature methanogenesis and psychrophilic methanogenic communities. The aim of the present work was to study methanogenesis in a wide range of temperatures with samples from sediments of deep lakes. These sediments may be considered deposits of different types of microorganisms, which are constantly exposed to low temperatures. The main question was how psychrophilic methanogenic microbial communities compare to mesophilic and thermophilic ones. Methanogenesis in a temperature range of 2–70°C was investigated using sediment samples from Baldegger lake (65 m) and Soppen lake (25 m), Switzerland. Methane production from organic matter of sediments occurred at all temperatures tested. An exponential dependence of methane production rate was found between 2 and 30°C. Methanogenesis occurred even at 70°C. At the same time stable methane production from organic matter of sediments was observed at temperatures below 10°C. Methanogenic microbial communities were enriched at different temperatures. The communities enriched at 4–8°C had the highest activity at low temperatures indicating that a specific psychrophilic community exists. Addition of substrates such as cellulose, volatile fatty acids (butyrate, propionate, acetate), methanol and H2/CO2 stimulated methane production at all temperatures. H2/CO2 as well as methanol were directly converted to methane under thermophilic conditions. At low temperatures these substrates were converted to methane by a two-step process. First acetate was formed, followed by methane production from acetate. When acetate concentrations were high, acetoclastic methanogenesis was inhibited at low temperatures. This reaction appears to be one of the “bottle neck” in psychrophilic methanogenesis.
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Donoso-Bravo, A., C. Retamal, M. Carballa, G. Ruiz-Filippi, and R. Chamy. "Influence of temperature on the hydrolysis, acidogenesis and methanogenesis in mesophilic anaerobic digestion: parameter identification and modeling application." Water Science and Technology 60, no. 1 (July 1, 2009): 9–17. http://dx.doi.org/10.2166/wst.2009.316.
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The effect of temperature on the kinetic parameters involved in the main reactions of the anaerobic digestion process was studied. Batch tests with starch, glucose and acetic acid as substrates for hydrolysis, acidogenesis and methanogenesis, respectively, were performed in a temperature range between 15 and 45°C. First order kinetics was assumed to determine the hydrolysis rate constant, while Monod and Haldane kinetics were considered for acidogenesis and methanogenesis, respectively. The results obtained showed that the anaerobic process is strongly influenced by temperature, with acidogenesis exerting the highest effect. The Cardinal Temperature Model 1 with an inflection point (CTM1) fitted properly the experimental data in the whole temperature range, except for the maximum degradation rate of acidogenesis. A simple case-study assessing the effect of temperature on an anaerobic CSTR performance indicated that with relatively simple substrates, like starch, the limiting reaction would change depending on temperature. However, when more complex substrates are used (e.g. sewage sludge), the hydrolysis might become more quickly into the limiting step.
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Jun, Wang, Xu Tingting, Yin Lichu, Han Cheng, Deng Huan, Jiang Yunbin, and Zhong Wenhui. "Nitrate addition inhibited methanogenesis in paddy soils under long-term managements." Plant, Soil and Environment 64, No. 8 (August 1, 2018): 393–99. http://dx.doi.org/10.17221/231/2018-pse.
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Rice fields are a major source of atmospheric methane (CH<sub>4</sub>). Nitrate has been approved to inhibit CH<sub>4</sub> production from paddy soils, while fertilization as well as water management can also affect the methanogenesis. It is unknown whether nitrate addition might result in shifts in the methanogenesis and methanogens in paddy soils influenced by different practices. Six paddy soils of different fertilizer types and groundwater tables were collected from a long-term experiment site. CH<sub>4</sub> production rate and methanogenic archaeal abundance were determined with and without nitrate addition in the microcosm incubation. The structure of methanogenic archaeal community was analysed using the PCR-DGGE (polymerase chain reaction denaturing gradient gel electrophoresis) and pyrosequencing. The results showed that nitrate addition significantly decreased the CH<sub>4</sub> production rate and methanogenic archaeal abundance in all six paddy soils by 70–100% and 54–88%, respectively. The quantity, position and relative intensity of DGGE bands exhibited differences when nitrate was added. Nitrate suppressed the growth of methanogenic archaeal species affiliated to Methanosaetaceae, unidentified Euryarchaeota, Thaumarchaeota and Methanosarinaceae. The universal inhibition of nitrate addition on the methanogenesis and methanogens can be adopted as a practice of mitigating CH<sub>4</sub> emission in paddy soils under different fertilization and water managements.
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Mogollón, J. M., A. W. Dale, H. Fossing, and P. Regnier. "Timescales for the development of methanogenesis and free gas layers in recently-deposited sediments of Arkona Basin (Baltic Sea)." Biogeosciences Discussions 8, no. 4 (August 1, 2011): 7623–69. http://dx.doi.org/10.5194/bgd-8-7623-2011.
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Abstract. Arkona Basin (southwestern Baltic Sea) is a seasonally-hypoxic basin characterized by the presence of free methane gas in its youngest organic-rich muddy stratum. Through the use of reactive transport models, this study tracks the development of the methane geochemistry in Arkona Basin as this muddy sediment becomes deposited during the last 8 kyr. Four cores are modeled each pertaining to a unique geochemical scenario according to their respective contemporary geochemical profiles. Ultimately the thickness of the muddy sediment and the flux of particulate organic carbon are crucial in determining the advent of both methanogenesis and free methane gas, the timescales over which methanogenesis takes over as a dominant reaction pathway for organic matter degradation, and the timescales required for free methane gas to form.
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Mogollón, J. M., A. W. Dale, H. Fossing, and P. Regnier. "Timescales for the development of methanogenesis and free gas layers in recently-deposited sediments of Arkona Basin (Baltic Sea)." Biogeosciences 9, no. 5 (May 30, 2012): 1915–33. http://dx.doi.org/10.5194/bg-9-1915-2012.
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Abstract. Arkona Basin (southwestern Baltic Sea) is a seasonally-hypoxic basin characterized by the presence of free methane gas in its youngest organic-rich muddy stratum. Through the use of reactive transport models, this study tracks the development of the methane geochemistry in Arkona Basin as this muddy sediment became deposited during the last 8 kyr. Four cores are modeled each pertaining to a unique geochemical scenario according to their respective contemporary geochemical profiles. Ultimately the thickness of the muddy sediment and the flux of particulate organic carbon are crucial in determining the advent of both methanogenesis and free methane gas, the timescales over which methanogenesis takes over as a dominant reaction pathway for organic matter degradation, and the timescales required for free methane gas to form.
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Peterson, Joseph R., Piyush Labhsetwar, Jeremy R. Ellermeier, Petra R. A. Kohler, Ankur Jain, Taekjip Ha, William W. Metcalf, and Zaida Luthey-Schulten. "Towards a Computational Model of a Methane Producing Archaeum." Archaea 2014 (2014): 1–18. http://dx.doi.org/10.1155/2014/898453.
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Progress towards a complete model of the methanogenic archaeumMethanosarcina acetivoransis reported. We characterized size distribution of the cells using differential interference contrast microscopy, finding them to be ellipsoidal with mean length and width of 2.9 μm and 2.3 μm, respectively, when grown on methanol and 30% smaller when grown on acetate. We used the single molecule pull down (SiMPull) technique to measure average copy number of the Mcr complex and ribosomes. A kinetic model for the methanogenesis pathways based on biochemical studies and recent metabolic reconstructions for several related methanogens is presented. In this model, 26 reactions in the methanogenesis pathways are coupled to a cell mass production reaction that updates enzyme concentrations. RNA expression data (RNA-seq) measured for cell cultures grown on acetate and methanol is used to estimate relative protein production per mole of ATP consumed. The model captures the experimentally observed methane production rates for cells growing on methanol and is most sensitive to the number of methyl-coenzyme-M reductase (Mcr) and methyl-tetrahydromethanopterin:coenzyme-M methyltransferase (Mtr) proteins. A draft transcriptional regulation network based on known interactions is proposed which we intend to integrate with the kinetic model to allow dynamic regulation.
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Akintola, George Oluwole, Francis Amponsah-Dacosta, Steven Rupprecht, Nithyadharseni Palaniyandy, Sphiwe Emmanuel Mhlongo, Wilson Mugera Gitari, and Joshua Nosa Edokpayi. "Methanogenesis Potentials: Insights from Mineralogical Diagenesis, SEM and FTIR Features of the Permian Mikambeni Shale of the Tuli Basin, Limpopo Province of South Africa." Minerals 11, no. 6 (June 19, 2021): 651. http://dx.doi.org/10.3390/min11060651.
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Carbonaceous shale is more topical than ever before due to the associated unconventional resources of methane. The use of FTIR, SEM-EDX, and mineralogical analyses has demonstrated a promising approach to assess methanogenesis potentials in a more rapid and reliable manner for preliminary prospecting. Representative core samples from the borehole that penetrated the carbonaceous Mikambeni shale Formations were investigated for methanogenesis potentials. The absorption band stretches from 1650 cm−1 to 1220 cm−1 in wavenumber, corresponding to C-O stretching and OH deformation of acetic and phenolic groups in all studied samples, thereby suggesting biogenic methanogenesis. The CO2 was produced by decarboxylation of organic matter around 2000 cm−1 and 2300 cm−1 and served as a source of the carboxylic acid that dissolved the feldspar. This dissolution process tended to release K+ ions, which facilitated the illitization of the smectite minerals. The SEM-EDX spectroscopy depicted a polyframboidal pyrite structure, which indicated a sulfate reduction of pyrite minerals resulting from microbial activities in an anoxic milieu and causes an increase in alkalinity medium that favors precipitation of dolomite in the presence of Ca and Mg as burial depth increases. The contact diagenesis from the proximity of Sagole geothermal spring via Tshipise fault is suggested to have enhanced the transformation of smectite to chlorite via a mixed layer corrensite in a solid-state gradual replacement reaction pathway. The presence of diagenetic chlorite mineral is characteristic of low-grade metamorphism or high diagenetic zone at a temperature around 200 °C to 230 °C and corresponds to thermal breakdown of kerogen to methane at strong absorption band around 2850 cm−1 and 3000 cm−1, indicating thermal methanogenesis.
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Bai, Liping, Takashi Fujishiro, Gangfeng Huang, Jürgen Koch, Atsushi Takabayashi, Makio Yokono, Ayumi Tanaka, et al. "Towards artificial methanogenesis: biosynthesis of the [Fe]-hydrogenase cofactor and characterization of the semi-synthetic hydrogenase." Faraday Discussions 198 (2017): 37–58. http://dx.doi.org/10.1039/c6fd00209a.
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The greenhouse gas and energy carrier methane is produced on Earth mainly by methanogenic archaea. In the hydrogenotrophic methanogenic pathway the reduction of one CO2 to one methane molecule requires four molecules of H2 containing eight electrons. Four of the electrons from two H2 are supplied for reduction of an electron carrier F420, which is catalyzed by F420-reducing [NiFe]-hydrogenase under nickel-sufficient conditions. The same reaction is catalysed under nickel-limiting conditions by [Fe]-hydrogenase coupled with a reaction catalyzed by F420-dependent methylene tetrahydromethanopterin dehydrogenase. [Fe]-hydrogenase contains an iron-guanylylpyridinol (FeGP) cofactor for H2 activation at the active site. FeII of FeGP is coordinated to a pyridinol-nitrogen, an acyl-carbon, two CO and a cysteine-thiolate. We report here on comparative genomic analyses of biosynthetic genes of the FeGP cofactor, which are primarily located in a hmd-co-occurring (hcg) gene cluster. One of the gene products is HcgB which transfers the guanosine monophosphate (GMP) moiety from guanosine triphosphate (GTP) to a pyridinol precursor. Crystal structure analysis of HcgB from Methanococcus maripaludis and its complex with 6-carboxymethyl-3,5-dimethyl-4-hydroxy-2-pyridinol confirmed the physiological guanylyltransferase reaction. Furthermore, we tested the properties of semi-synthetic [Fe]-hydrogenases using the [Fe]-hydrogenase apoenzyme from several methanogenic archaea and a mimic of the FeGP cofactor. On the basis of the enzymatic reactions involved in the methanogenic pathway, we came up with an idea how the methanogenic pathway could be simplified to develop an artificial methanogenesis system.
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Burke, Stephen A., Sam L. Lo, and Joseph A. Krzycki. "Clustered Genes Encoding the Methyltransferases of Methanogenesis from Monomethylamine." Journal of Bacteriology 180, no. 13 (July 1, 1998): 3432–40. http://dx.doi.org/10.1128/jb.180.13.3432-3440.1998.
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ABSTRACT Coenzyme M (CoM) is methylated during methanogenesis from monomethyamine in a reaction catalyzed by three proteins. Using monomethylamine, a 52-kDa polypeptide termed monomethylamine methyltransferase (MMAMT) methylates the corrinoid cofactor bound to a second polypeptide, monomethylamine corrinoid protein (MMCP). Methylated MMCP then serves as a substrate for MT2-A, which methylates CoM. The genes for these proteins are clustered on 6.8 kb of DNA inMethanosarcina barkeri MS. The gene encoding MMCP (mtmC) is located directly upstream of the gene encoding MMAMT (mtmB). The gene encoding MT2-A (mtbA) was found 1.1 kb upstream of mtmC, but no obvious open reading frame was found in the intergenic region betweenmtbA and mtmC. A single monocistronic transcript was found for mtbA that initiated 76 bp from the translational start. Separate transcripts of 2.4 and 4.7 kb were detected, both of which carried mtmCB. The larger transcript also encoded mtmP, which is homologous to the APC family of cationic amine permeases and may therefore encode a methylamine permease. A single transcriptional start site was found 447 bp upstream of the translational start of mtmC. MtmC possesses the corrinoid binding motif found in corrinoid proteins involved in dimethylsulfide- and methanol-dependent methanogenesis, as well as in methionine synthase. The open reading frame ofmtmB was interrupted by a single in-frame, midframe, UAG codon which was also found in mtmB from M. barkeri NIH. A mechanism that circumvents UAG-directed termination of translation must operate during expression ofmtmB in this methanogen.
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Kobayashi, Hajime, Ryohei Toyoda, Hiroyuki Miyamoto, Yasuhito Nakasugi, Yuki Momoi, Kohei Nakamura, Qian Fu, Haruo Maeda, Takashi Goda, and Kozo Sato. "Analysis of a Methanogen and an Actinobacterium Dominating the Thermophilic Microbial Community of an Electromethanogenic Biocathode." Archaea 2021 (March 1, 2021): 1–13. http://dx.doi.org/10.1155/2021/8865133.
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Electromethanogenesis refers to the bioelectrochemical synthesis of methane from CO2 by biocathodes. In an electromethanogenic system using thermophilic microorganisms, metagenomic analysis along with quantitative real-time polymerase chain reaction and fluorescence in situ hybridization revealed that the biocathode microbiota was dominated by the methanogen Methanothermobacter sp. strain EMTCatA1 and the actinobacterium Coriobacteriaceae sp. strain EMTCatB1. RNA sequencing was used to compare the transcriptome profiles of each strain at the methane-producing biocathodes with those in an open circuit and with the methanogenesis inhibitor 2-bromoethanesulfonate (BrES). For the methanogen, genes related to hydrogenotrophic methanogenesis were highly expressed in a manner similar to those observed under H2-limited conditions. For the actinobacterium, the expression profiles of genes encoding multiheme c-type cytochromes and membrane-bound oxidoreductases suggested that the actinobacterium directly takes up electrons from the electrode. In both strains, various stress-related genes were commonly induced in the open-circuit biocathodes and biocathodes with BrES. This study provides a molecular inventory of the dominant species of an electromethanogenic biocathode with functional insights and therefore represents the first multiomics characterization of an electromethanogenic biocathode.
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McCarty, P. L., and F. E. Mosey. "Modelling of Anaerobic Digestion Processes (A Discussion of Concepts)." Water Science and Technology 24, no. 8 (October 1, 1991): 17–33. http://dx.doi.org/10.2166/wst.1991.0216.
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The concepts behind some of the more widely used mathematical models of the anaerobic digestion process are described and discussed together with some recent microbiological and biochemical studies that might provide a basis for the next generation of mathematical models. First order rate equations are commonly used for the initial hydrolysis of complex organics and Monod kinetics are widely used to describe methanogenesis from acetate. Depending on circumstances, either of these reactions may be considered as the rate-limiting reaction of the overall fermentation. Thermodynamic calculations provide a valuable tool for modelling intermediate metabolism but the metabolic repertoire of these bacteria still provides a few surprises for the fermentation chemist. A possible new concept for modelling patterns of volatile fatty acids during overload and recovery of anaerobic digesters is described and discussed.
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Liu, Ru, Ying Hao Song, and Huan Sheng Wang. "Study on Anaerobic Simultaneous Denitrification and Methanogenesis Combined with Shortcut Nitrification Process Treating Piggery Wastewater." Applied Mechanics and Materials 178-181 (May 2012): 680–87. http://dx.doi.org/10.4028/www.scientific.net/amm.178-181.680.
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An expanded granular sludge bed (EGSB) was combined with an anaerobic/anoxic/oxic process (A2/O) to treat piggery wastewater, in which the EGSB was used as a simultaneous methanogenesis and denitrification reactor and the A2/O as an shortcut nitrification reactor. The results showed that: 1) The COD of effluent in anaerobic reactor increased in earlier stage and decreased in later stage with increasing reflux ratios each time, and reached to about 550 mg/L finally. The COD removal efficiencies of the whole process were about 150 mg/L, and almost not affected by different reflux ratios. 2) Simultaneous denitrification and methanogenesis realized successfully after the aerobic effluent recirculated to the anaerobic reactor. The highest nitrite loading reached 1.48 kg/m3.d with constant increase of reflux ratio, while nitrite removal efficiencies were always 100%. 3) Short-cut nitrification was perfored steadily in the whole combined system. When reflux ratios were 50%, 100%, 200%, 300%, respectively, ammonia nitrogen removal efficiencies were all 100%, and total nitrogen removal efficiencies were 52.3%, 53.1%, 68.7%,85.1%, respectively. 4) The first reaction was denitrification when nitrite was recycled to anaerobic reactor, so methane contents were very little in earlier stage with increasing reflux ratios every time, but increased gradually after a period of operation.
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Berger, Stefanie, Cornelia Welte, and Uwe Deppenmeier. "Acetate Activation inMethanosaeta thermophila: Characterization of the Key Enzymes Pyrophosphatase and Acetyl-CoA Synthetase." Archaea 2012 (2012): 1–10. http://dx.doi.org/10.1155/2012/315153.
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The thermophilic methanogenMethanosaeta thermophilauses acetate as sole substrate for methanogenesis. It was proposed that the acetate activation reaction that is needed to feed acetate into the methanogenic pathway requires the hydrolysis of two ATP, whereas the acetate activation reaction inMethanosarcina sp.is known to require only one ATP. As these organisms live at the thermodynamic limit that sustains life, the acetate activation reaction inMt. thermophilaseems too costly and was thus reevaluated. It was found that of the putative acetate activation enzymes one gene encoding an AMP-forming acetyl-CoA synthetase was highly expressed. The corresponding enzyme was purified and characterized in detail. It catalyzed the ATP-dependent formation of acetyl-CoA, AMP, and pyrophosphate(PPi)and was only moderately inhibited byPPi. The breakdown ofPPiwas performed by a soluble pyrophosphatase. This enzyme was also purified and characterized. The pyrophosphatase hydrolyzed the major part ofPPi(KM=0.27±0.05 mM) that was produced in the acetate activation reaction. Activity was not inhibited by nucleotides orPPi. However, it cannot be excluded that otherPPi-dependent enzymes take advantage of the remainingPPiand contribute to the energy balance of the cell.
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Fagundes, Gisele M., Gabriela Benetel, Mateus M. Carriero, Ricardo L. M. Sousa, James P. Muir, Robert O. Macedo, and Ives C. S. Bueno. "Tannin-rich forage as a methane mitigation strategy for cattle and the implications for rumen microbiota." Animal Production Science 61, no. 1 (2021): 26. http://dx.doi.org/10.1071/an19448.
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Context Methane from ruminant livestock systems contributes to the greenhouse effect on the environment, which justifies the adoption of novel feed strategies that mitigate enteric emissions. Aims We investigated the effects of the condensed tannin (CT)-rich legumes Flemingia macrophylla, Leucaena leucocephala, Stylosanthes guianensis, Gliricidia sepium, Cratylia argentea, Cajanus cajan, Desmodium ovalifolium, Macrotyloma axillare, Desmodium paniculatum and Lespedeza procumbens on in vitro methane emissions and rumen microbiota for beef cattle. Methods Four rumen-cannulated Nellore cattle grazing a tropical grass pasture were used as inoculum donors. Key results Real-time quantitative polymerase chain reaction analysis revealed that the abundance of Ruminococcus flavefaciens, methanogenic archaea and protozoa populations were reduced (P £ 0.05), whereas total ruminal bacteria were enhanced in the presence of CT. Our study also revealed a positive (P £ 0.05) relationship between CT and Fibrobacter succinogenes abundance. Reactive CT from L. leucocephala, D. paniculatum and L. procumbens resulted in decreased (P £ 0.05) isoacid content and methane production. Conclusions L. leucocephala, D. paniculatum and L. procumbens have the potential to suppress rumen methanogenesis. However, in vitro fermentation of L. leucocephala resulted in greater (P £ 0.05) degradability percentages than the other two species. Implications CT in legume species will have potential as part of an overall nutritional strategy to manipulate rumen microbiota and mitigate enteric methanogenesis in livestock production systems.
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Kalyuzhnyi, Sergey, and Vyacheslav Fedorovich. "Integrated mathematical model of UASB reactor for competition between sulphate reduction and methanogenesis." Water Science and Technology 36, no. 6-7 (September 1, 1997): 201–8. http://dx.doi.org/10.2166/wst.1997.0592.
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The existing mathematical models of anaerobic treatment processes were mainly developed for ideally mixed reactors with no concentration gradients on substrates, intermediates, products and bacteria inside the reactor. But for conventional UASB reactors with low upward velocity, the distribution of these components along the reactor height is very far from uniform. This paper presents an integrated mathematical model of the functioning of UASB reactor taking into account this non-uniformity as well as multiple-reaction stoichiometry and kinetics. In general, our integrated model includes the following blocks: a) kinetic block, including the growth and metabolism of acidogenic, acetogenic, methanogenic and sulphate-reducing bacteria; b) physico-chemical block, for the calculation of pH in each compartment of the liquid phase; c) hydrodynamic block, describing liquid flow as well as the transport and distribution of the components along the reactor height; d) transfer block, describing a mass transfer of gaseous components from the liquid to gas phase. This model was calibrated to some experimental studies of the functioning of UASB reactors made by in 1994. Hypothetical computer simulations are presented to illustrate the influence of different factors (recycle number, hydraulic retention time, quality of seed sludge, SO42−:COD ratio etc.) on the operation performance of UASB reactor.
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Guyot, J. P. "Role of formate in methanogenesis from xylan byCellulomonassp. associated with methanogens andDesulfovibrio vulgaris: Inhibition of the aceticlastic reaction." FEMS Microbiology Letters 34, no. 2 (April 1986): 149–53. http://dx.doi.org/10.1111/j.1574-6968.1986.tb01395.x.
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Elul, Michal, Maxim Rubin-Blum, Zeev Ronen, Itay Bar-Or, Werner Eckert, and Orit Sivan. "Metagenomic insights into the metabolism of microbial communities that mediate iron and methane cycling in Lake Kinneret iron-rich methanic sediments." Biogeosciences 18, no. 6 (March 23, 2021): 2091–106. http://dx.doi.org/10.5194/bg-18-2091-2021.
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Abstract. Complex microbial communities facilitate iron and methane transformations in anoxic methanic sediments of freshwater lakes, such as Lake Kinneret (the Sea of Galilee, Israel). The phylogenetic and functional diversity of these consortia are not fully understood, and it is not clear which lineages perform iron reduction and anaerobic oxidation of methane (AOM). Here, we investigated microbial communities from both natural Lake Kinneret iron-rich methanic sediments (>20 cm depth) and iron-amended slurry incubations from this zone using metagenomics, focusing on functions associated with iron reduction and methane cycling. Analyses of the phylogenetic and functional diversity indicate that consortia of archaea (mainly Bathyarchaeia, Methanomicrobia, Thermoplasmata, and Thermococci) and bacteria (mainly Chloroflexi (Chloroflexota), Nitrospirae (Nitrospirota), and Proteobacteria) perform key metabolic reactions such as amino acid uptake and dissimilation, organic matter fermentation, and methanogenesis. The Deltaproteobacteria, especially Desulfuromondales (Desulfuromonadota), have the potential to transfer electrons extracellularly either to iron mineral particles or to microbial syntrophs, including methanogens. This is likely via transmembrane cytochromes, outer-membrane hexaheme c-type cytochrome (OmcS) in particular, or pilin monomers (PilA), all of which were attributed to this lineage. Bona fide anaerobic oxidizers of methane (ANME) and denitrifying methanotrophs Methylomirabilia (NC10) may mediate AOM in these methanogenic sediments; however we also consider the role of methanogens in active AOM or back flux of methanogenesis. Putative aerobes, such as methane-oxidizing bacteria Methylomonas and their methylotrophic syntrophs Methylotenera, are found among the anaerobic lineages in Lake Kinneret iron-amended slurries and are also involved in the oxidation of methane or its intermediates, as suggested previously. We propose a reaction model for the metabolic interactions in these sediments, linking the potential players that interact via intricate metabolic tradeoffs and direct electron transfer between species. Our results highlight the metabolic complexity of microbial communities in an energy-limited environment, where aerobe and anaerobe communities may co-exist and facilitate AOM as one strategy for survival.
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Vavilin, V. A., M. Yu Schelkanov, L. Ya Lokshina, S. V. Rytov, J. Jokela, E. Salminen, and J. Rintala. "A comparative analysis of a balance between the rates of polymer hydrolysis and acetoclastic methanogenesis during anaerobic digestion of solid waste." Water Science and Technology 45, no. 10 (May 1, 2002): 249–54. http://dx.doi.org/10.2166/wst.2002.0345.
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A distributed model of anaerobic digestion of solid waste was developed. Waste, volatile fatty acids (VFA), methanogenic biomass and methane concentrations were the model variables. A system of parabolic partial differential equations in the one space variable and time with slab, cylindrical or spherical symmetry of the problem was solved numerically. Diffusion of VFA inhibiting both polymer hydrolysis and acetoclastic methanogenesis was taken into account. The model showed that concentration waves of methanogenic biomass and VFA propagated over reaction space. Diffusion-based “acceleration” of methane production in the reactor was possible when intensity of VFA utilisation in the methanogenic area was sufficient for complete digestion of incoming VFA. Otherwise, methanogenic area propagation would be suppressed. Optimum conditions for the solid waste digestion can be reached at low mass transfer at the beginning and at high mass transfer when methanogenic population increases. If the initial methanogenic biomass was localised at the centre of the reactor, the total reaction time was shorter as compared to the case when the initial biomass was uniformly distributed over the reactor volume. In the last case, there was no concentration wave propagation.
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Signor, Luca, Carola Knuppe, Robert Hug, Bernd Schweizer, Andreas Pfaltz, and Bernhard Jaun. "Methane Formation by Reaction of a Methyl Thioether with a Photo-Excited Nickel Thiolate—A Process Mimicking Methanogenesis in Archaea." Chemistry – A European Journal 6, no. 19 (September 18, 2000): 3508–16. http://dx.doi.org/10.1002/1521-3765(20001002)6:19<3508::aid-chem3508>3.0.co;2-w.
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Signor, Luca, Carola Knuppe, Robert Hug, Bernd Schweizer, Andreas Pfaltz, and Bernhard Jaun. "Methane Formation by Reaction of a Methyl Thioether with a Photo-Excited Nickel Thiolate—A Process Mimicking Methanogenesis in Archaea." Chemistry - A European Journal 6, no. 19 (October 2, 2000): 3508–16. http://dx.doi.org/10.1002/1521-3765(20001002)6:19<3508::aid-chem3508>3.3.co;2-n.
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Wuerfel, Oliver, Frank Thomas, Marcel Sven Schulte, Reinhard Hensel, and Roland Arturo Diaz-Bone. "Mechanism of multi-metal(loid) methylation and hydride generation by methylcobalamin and cob(I)alamin: a side reaction of methanogenesis." Applied Organometallic Chemistry 26, no. 2 (January 10, 2012): 94–101. http://dx.doi.org/10.1002/aoc.2821.
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Laufer, Kerstin, Bernhard Eikmanns, Ursula Frimmer, and Rudolf K. Thauer. "Methanogenesis from Acetate by Methanosarcina barkeri: Catalysis of Acetate Formation from Methyl Iodide, CO2 , and H2 by the Enzyme System Involved." Zeitschrift für Naturforschung C 42, no. 4 (April 1, 1987): 360–72. http://dx.doi.org/10.1515/znc-1987-0407.
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Cell suspensions of Methanosarcina barkeri grown on acetate catalyze the formation of methane and CO2 from acetate as well as an isotopic exchange between the carboxyl group of acetate and CO2. Here we report that these cells also mediate the synthesis of acetate from methyl iodide, CO2, and reducing equivalents (H2 or CO), the methyl group of acetate being derived from methyl iodide and the carboxyl group from CO2. Methyl chloride and methyltosylate but not methanol can substitute for methyl iodide in this reaction. Acetate formation from methyl iodide, CO2, and reducing equivalents is coupled with the phosphorylation of ADP. Evidence is presented that methyl iodide is incorporated into the methyl group of acetate via a methyl corrinoid intermediate (deduced from inhibition experiments with propyl iodide) and that CO2 is assimilated into the carboxyl group via a C1 intermediate which does not exchange with free formate or free CO. The effects of protonophores, of the proton-translocating ATPase inhibitor N.N′-di- cyclohexylcarbodiimide, and of arsenate on acetate formation are interpreted to indicate that the reduction of CO2 to the oxidation level of the carboxyl group of acetate requires the presence of an electrochemical proton potential and that acetyl-CoA or acetyl-phosphate rather than free acetate is the immediate product of the condensation reaction. These results are discussed with respect to the mechanism of methanogenesis from acetate.
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Oren, Aharon. "Bioenergetic Aspects of Halophilism." Microbiology and Molecular Biology Reviews 63, no. 2 (June 1, 1999): 334–48. http://dx.doi.org/10.1128/mmbr.63.2.334-348.1999.
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SUMMARY Examinination of microbial diversity in environments of increasing salt concentrations indicates that certain types of dissimilatory metabolism do not occur at the highest salinities. Examples are methanogenesis for H2 + CO2 or from acetate, dissimilatory sulfate reduction with oxidation of acetate, and autotrophic nitrification. Occurrence of the different metabolic types is correlated with the free-energy change associated with the dissimilatory reactions. Life at high salt concentrations is energetically expensive. Most bacteria and also the methanogenic archaea produce high intracellular concentrations of organic osmotic solutes at a high energetic cost. All halophilic microorganisms expend large amounts of energy to maintain steep gradients of NA+ and K+ concentrations across their cytoplasmic membrane. The energetic cost of salt adaptation probably dictates what types of metabolism can support life at the highest salt concentrations. Use of KCl as an intracellular solute, while requiring far-reaching adaptations of the intracellular machinery, is energetically more favorable than production of organic-compatible solutes. This may explain why the anaerobic halophilic fermentative bacteria (order Haloanaerobiales) use this strategy and also why halophilic homoacetogenic bacteria that produce acetate from H2 + CO2 exist whereas methanogens that use the same substrates in a reaction with a similar free-energy yield do not.
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Schink, B. "Energetics of syntrophic cooperation in methanogenic degradation." Microbiology and Molecular Biology Reviews 61, no. 2 (June 1997): 262–80. http://dx.doi.org/10.1128/mmbr.61.2.262-280.1997.
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Fatty acids and alcohols are key intermediates in the methanogenic degradation of organic matter, e.g., in anaerobic sewage sludge digestors or freshwater lake sediments. They are produced by classical fermenting bacteria for disposal of electrons derived in simultaneous substrate oxidations. Methanogenic bacteria can degrade primarily only one-carbon compounds. Therefore, acetate, propionate, ethanol, and their higher homologs have to be fermented further to one-carbon compounds. These fermentations are called secondary or syntrophic fermentations. They are endergonic processes under standard conditions and depend on intimate coupling with methanogenesis. The energetic situation of the prokaryotes cooperating in these processes is problematic: the free energy available in the reactions for total conversion of substrate to methane attributes to each partner amounts of energy in the range of the minimum biochemically convertible energy, i.e., 20 to 25 kJ per mol per reaction. This amount corresponds to one-third of an ATP unit and is equivalent to the energy required for a monovalent ion to cross the charged cytoplasmic membrane. Recent studies have revealed that syntrophically fermenting bacteria synthesize ATP by substrate-level phosphorylation and reinvest part of the ATP-bound energy into reversed electron transport processes, to release the electrons at a redox level accessible by the partner bacteria and to balance their energy budget. These findings allow us to understand the energy economy of these bacteria on the basis of concepts derived from the bioenergetics of other microorganisms.
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Vakili, A., M. Danesh Mesgaran, H. Jahani-Azizabadi, S. Ghovvati, E. Milani, and F. Rezaee. "The effect of non-fibre carbohydrates supplementation on methanogenesis bacteria and protozoa populations in rumen fluid as determined by real-time polymerase chain reaction." Advances in Animal Biosciences 1, no. 1 (April 2010): 253. http://dx.doi.org/10.1017/s2040470010003961.
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Khan, Munawwar A., Poojabahen G. Patel, Arpitha G. Ganesh, Naushad Rais, Sultan M. Faheem, and Shams T. Khan. "Assessing Methanogenic Archaeal Community in Full Scale Anaerobic Sludge Digester Systems in Dubai, United Arab Emirates." Open Microbiology Journal 12, no. 1 (April 30, 2018): 123–34. http://dx.doi.org/10.2174/1874285801812010123.
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Introduction:Anaerobic digestion for methane production comprises of an exceptionally diverse microbial consortium, a profound understanding about which is still constrained. In this study, the methanogenic archaeal communities in three full-scale anaerobic digesters of a Municipal Wastewater Treatment Plant were analyzed by Fluorescencein situhybridization and quantitative real-time Polymerase Chain Reaction (qPCR) technique.Methods & Materials:Fluorescencein situhybridization (FISH) was performed to detect and quantify the methanogenicArchaeain the sludge samples whereas qPCR was carried out to support the FISH analysis. Multiple probes targeting domain archaea, different orders and families of Archaea were used for the studies.Results and Discussion:In general, the aceticlastic organisms(Methanosarcinaceae & Methanosaetaceae)were more abundant than the hydrogenotrophic organisms(Methanobacteriales, Methanomicrobiales, Methanobacteriaceae & Methanococcales). Both FISH and qPCR indicated that familyMethanosaetaceaewas the most abundant suggesting that aceticlastic methanogenesis is probably the dominant methane production pathway in these digesters.Conclusion:Future work involving high-throughput sequencing methods and correlating archaeal communities with the main operational parameters of anaerobic digesters will help to obtain a better understanding of the dynamics of the methanogenic archaeal community in wastewater treatment plants in United Arab Emirates (UAE) which in turn would lead to improved performance of anaerobic sludge digesters.
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McDermott, Jill M., Jeffrey S. Seewald, Christopher R. German, and Sean P. Sylva. "Pathways for abiotic organic synthesis at submarine hydrothermal fields." Proceedings of the National Academy of Sciences 112, no. 25 (June 8, 2015): 7668–72. http://dx.doi.org/10.1073/pnas.1506295112.
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Arguments for an abiotic origin of low-molecular weight organic compounds in deep-sea hot springs are compelling owing to implications for the sustenance of deep biosphere microbial communities and their potential role in the origin of life. Theory predicts that warm H2-rich fluids, like those emanating from serpentinizing hydrothermal systems, create a favorable thermodynamic drive for the abiotic generation of organic compounds from inorganic precursors. Here, we constrain two distinct reaction pathways for abiotic organic synthesis in the natural environment at the Von Damm hydrothermal field and delineate spatially where inorganic carbon is converted into bioavailable reduced carbon. We reveal that carbon transformation reactions in a single system can progress over hours, days, and up to thousands of years. Previous studies have suggested that CH4 and higher hydrocarbons in ultramafic hydrothermal systems were dependent on H2 generation during active serpentinization. Rather, our results indicate that CH4 found in vent fluids is formed in H2-rich fluid inclusions, and higher n-alkanes may likely be derived from the same source. This finding implies that, in contrast with current paradigms, these compounds may form independently of actively circulating serpentinizing fluids in ultramafic-influenced systems. Conversely, widespread production of formate by ΣCO2 reduction at Von Damm occurs rapidly during shallow subsurface mixing of the same fluids, which may support anaerobic methanogenesis. Our finding of abiogenic formate in deep-sea hot springs has significant implications for microbial life strategies in the present-day deep biosphere as well as early life on Earth and beyond.
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Liyanage, T. U. Habarakada, and Sandhya Babel. "Enhancement of Methane Production in Anaerobic Digestion of Food Waste using Thermal Pretreatment." Environment and Natural Resources Journal 20, no. 1 (September 21, 2021): 1–9. http://dx.doi.org/10.32526/ennrj/20/202100063.
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Anaerobic digestion (AD) is an energy production process and food waste is a potential feedstock. The main biochemical reactions are Hydrolysis, Acidogenesis, Acetogenesis, and Methanogenesis. The hydrolysis step acts as the rate-limiting reaction and the pretreatment of the feedstocks can be used to support this step. In this research, thermal pretreatment was used as a potential method for food waste pretreatment. Six different pretreatment conditions were used: two different temperatures (80oC and 100oC) and three different pretreatment times (30, 60, and 90 min). The Bio-Methane Potential (BMP) test was conducted using 120 mL serum bottles for 20 days to determine the most suitable pretreatment conditions. An experiment was also conducted at the selected optimal conditions (80oC for 90 min) using a small-scale bioreactor against the control with a NaHCO3 buffer solution. The highest Soluble Chemical Oxygen Demand (SCOD) was observed at 100oC for 90 min. The optimal pretreatment was selected as 80oC for 90 min, which produced 14.75 mL/g VS of methane while the control produced 8.64 mL/g VS in BMP test. After a few days, the methane production started to slow down due to a decrease in pH. When a buffer was added, a specific methane yield of 120.13 mL/g VS was observed in the small-scale bioreactor. This was an 11.24% increase compared to the buffered control without thermal pretreatment. In conclusion, thermal pretreatment has a potential to enhance the AD but it is economical to use with less biodegradable waste than food waste.
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Jiménez, Núria, Hans H. Richnow, Carsten Vogt, Tina Treude, and Martin Krüger. "Methanogenic Hydrocarbon Degradation: Evidence from Field and Laboratory Studies." Journal of Molecular Microbiology and Biotechnology 26, no. 1-3 (2016): 227–42. http://dx.doi.org/10.1159/000441679.
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Microbial transformation of hydrocarbons to methane is an environmentally relevant process taking place in a wide variety of electron acceptor-depleted habitats, from oil reservoirs and coal deposits to contaminated groundwater and deep sediments. Methanogenic hydrocarbon degradation is considered to be a major process in reservoir degradation and one of the main processes responsible for the formation of heavy oil deposits and oil sands. In the absence of external electron acceptors such as oxygen, nitrate, sulfate or Fe(III), fermentation and methanogenesis become the dominant microbial metabolisms. The major end product under these conditions is methane, and the only electron acceptor necessary to sustain the intermediate steps in this process is CO<sub>2</sub>, which is itself a net product of the overall reaction. We are summarizing the state of the art and recent advances in methanogenic hydrocarbon degradation research. Both the key microbial groups involved as well as metabolic pathways are described, and we discuss the novel insights into methanogenic hydrocarbon-degrading populations studied in laboratory as well as environmental systems enabled by novel cultivation-based and molecular approaches. Their possible implications on energy resources, bioremediation of contaminated sites, deep-biosphere research, and consequences for atmospheric composition and ultimately climate change are also addressed.
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Kurth, Julia Maria, Marie-Caroline Müller, Cornelia Ulrike Welte, and Tristan Wagner. "Structural Insights into the Methane-Generating Enzyme from a Methoxydotrophic Methanogen Reveal a Restrained Gallery of Post-Translational Modifications." Microorganisms 9, no. 4 (April 14, 2021): 837. http://dx.doi.org/10.3390/microorganisms9040837.
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Methanogenic archaea operate an ancient, if not primordial, metabolic pathway that releases methane as an end-product. This last step is orchestrated by the methyl-coenzyme M reductase (MCR), which uses a nickel-containing F430-cofactor as the catalyst. MCR astounds the scientific world by its unique reaction chemistry, its numerous post-translational modifications, and its importance in biotechnology not only for production but also for capturing the greenhouse gas methane. In this report, we investigated MCR natively isolated from Methermicoccus shengliensis. This methanogen was isolated from a high-temperature oil reservoir and has recently been shown to convert lignin and coal derivatives into methane through a process called methoxydotrophic methanogenesis. A methoxydotrophic culture was obtained by growing M. shengliensis with 3,4,5-trimethoxybenzoate as the main carbon and energy source. Under these conditions, MCR represents more than 12% of the total protein content. The native MCR structure refined at a resolution of 1.6-Å precisely depicts the organization of a dimer of heterotrimers. Despite subtle surface remodeling and complete conservation of its active site with other homologues, MCR from the thermophile M. shengliensis contains the most limited number of post-translational modifications reported so far, questioning their physiological relevance in other relatives.
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Meng, Yu, Cheryl Ingram-Smith, Leroy L. Cooper, and Kerry S. Smith. "Characterization of an Archaeal Medium-Chain Acyl Coenzyme A Synthetase from Methanosarcina acetivorans." Journal of Bacteriology 192, no. 22 (September 17, 2010): 5982–90. http://dx.doi.org/10.1128/jb.00600-10.
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ABSTRACT Short- and medium-chain acyl coenzyme A (acyl-CoA) synthetases catalyze the formation of acyl-CoA from an acyl substrate, ATP, and CoA. These enzymes catalyze mechanistically similar two-step reactions that proceed through an enzyme-bound acyl-AMP intermediate. Here we describe the characterization of a member of this enzyme family from the methane-producing archaeon Methanosarcina acetivorans. This enzyme, a medium-chain acyl-CoA synthetase designated MacsMa, utilizes 2-methylbutyrate as its preferred substrate for acyl-CoA synthesis but cannot utilize acetate and thus cannot catalyze the first step of acetoclastic methanogenesis in M. acetivorans. When propionate or other less favorable acyl substrates, such as butyrate, 2-methylpropionate, or 2-methylvalerate, were utilized, the acyl-CoA was not produced or was produced at reduced levels. Instead, acyl-AMP and PPi were released in the absence of CoA, whereas in the presence of CoA, the intermediate was broken down into AMP and the acyl substrate, which were released along with PPi. These results suggest that although acyl-CoA synthetases may have the ability to utilize a broad range of substrates for the acyl-adenylate-forming first step of the reaction, the intermediate may not be suitable for the thioester-forming second step. The MacsMa structure has revealed the putative acyl substrate- and CoA-binding pockets. Six residues proposed to form the acyl substrate-binding pocket, Lys256, Cys298, Gly351, Trp259, Trp237, and Trp254, were targeted for alteration. Characterization of the enzyme variants indicates that these six residues are critical in acyl substrate binding and catalysis, and even conservative alterations significantly reduced the catalytic ability of the enzyme.
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López-Días, Borrego, Blanco, Bechtel, and Püttmann. "Significance of the High Abundance of Pentacyclic Triterpenyl and Hopenyl Acetates in Sphagnum Peat Bogs from Northern Spain." Quaternary 2, no. 3 (August 21, 2019): 30. http://dx.doi.org/10.3390/quat2030030.
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Global warming is expected to increase the rate of CH4 emission from acidic peatlands leading to an increased interest on its mechanisms of formation. The main routes are through the reduction of CO2 by molecular hydrogen and through the cleavage of acetate. A predominance of the former, a reaction which also competes with homoacetogenesis to form acetate, may enrich the media in acetate, which could potentially be incorporated in the peat molecular markers. Acetates of triterpenoid biomarkers have been identified in peats and lake sediments and related to the input of higher plants. Nevertheless, the acetyl derivatives are found in very low amounts in fresh plants and in much lower amount than other derivatives with alcohol or ketone functional groups. The dichloromethane/methanol extracts of Asturian peat bog profiles (North Spain) were analyzed using gas chromatography/mass spectrometry (GC/MS) and compound-specific-isotope-analysis (CSIA). They show abundance of acetates of compounds with oleanane, ursane, and lupane skeletons derived from higher plants and with hopane skeleton, which can be considered a characteristic of these peats. Two families of 3-oxyhopenyl acetates with -17(21)- and -22(29)- configurations were detected in the upper part of the peat profiles, having a δ13C isotopic composition enriched by 4‰ compared with that of higher plant triterpenoids, and similar to that of microorganism-derived regular hopanoids. Both the acetate and ketone derivatives with the oxygenated functionality at C-3 were generally present in a given extract and tended to accumulate at certain depth in the profiles and in specific levels. The widespread occurrence of acetyl-derivatives, their higher concentration in the deeper layers of the peat, the fact that the acetates correspond to different compound families of diverse source and the very low amount of acetates identified in Ericaceae-contributing to the peat compared to the alcohols suggest that they were formed in the peat under particularly favorable environmental conditions. We postulate that these conditions could have been the existence of a medium enriched in acetic acid produced by the dominance of hydrogenotrophic methanogenesis and/or homoacetogenesis over acetoclastic methanogenesis. This phenomenon that has been preferentially described in Sphagnum bogs at high latitudes, and in the deeper layers of peat, appears to be also present in the temperate peats of the Asturian coast.
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Sousa, Filipa L., Thorsten Thiergart, Giddy Landan, Shijulal Nelson-Sathi, Inês A. C. Pereira, John F. Allen, Nick Lane, and William F. Martin. "Early bioenergetic evolution." Philosophical Transactions of the Royal Society B: Biological Sciences 368, no. 1622 (July 19, 2013): 20130088. http://dx.doi.org/10.1098/rstb.2013.0088.
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Life is the harnessing of chemical energy in such a way that the energy-harnessing device makes a copy of itself. This paper outlines an energetically feasible path from a particular inorganic setting for the origin of life to the first free-living cells. The sources of energy available to early organic synthesis, early evolving systems and early cells stand in the foreground, as do the possible mechanisms of their conversion into harnessable chemical energy for synthetic reactions. With regard to the possible temporal sequence of events, we focus on: (i) alkaline hydrothermal vents as the far-from-equilibrium setting, (ii) the Wood–Ljungdahl (acetyl-CoA) pathway as the route that could have underpinned carbon assimilation for these processes, (iii) biochemical divergence, within the naturally formed inorganic compartments at a hydrothermal mound, of geochemically confined replicating entities with a complexity below that of free-living prokaryotes, and (iv) acetogenesis and methanogenesis as the ancestral forms of carbon and energy metabolism in the first free-living ancestors of the eubacteria and archaebacteria, respectively. In terms of the main evolutionary transitions in early bioenergetic evolution, we focus on: (i) thioester-dependent substrate-level phosphorylations, (ii) harnessing of naturally existing proton gradients at the vent–ocean interface via the ATP synthase, (iii) harnessing of Na + gradients generated by H + /Na + antiporters, (iv) flavin-based bifurcation-dependent gradient generation, and finally (v) quinone-based (and Q-cycle-dependent) proton gradient generation. Of those five transitions, the first four are posited to have taken place at the vent. Ultimately, all of these bioenergetic processes depend, even today, upon CO 2 reduction with low-potential ferredoxin (Fd), generated either chemosynthetically or photosynthetically, suggesting a reaction of the type ‘reduced iron → reduced carbon’ at the beginning of bioenergetic evolution.
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Chuang, Pei-Chuan, Megan B. Young, Andrew W. Dale, Laurence G. Miller, Jorge A. Herrera-Silveira, and Adina Paytan. "Methane and sulfate dynamics in sediments from mangrove-dominated tropical coastal lagoons, Yucatán, Mexico." Biogeosciences 13, no. 10 (May 23, 2016): 2981–3001. http://dx.doi.org/10.5194/bg-13-2981-2016.
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Abstract. Porewater profiles in sediment cores from mangrove-dominated coastal lagoons (Celestún and Chelem) on the Yucatán Peninsula, Mexico, reveal the widespread coexistence of dissolved methane and sulfate. This observation is interesting since dissolved methane in porewaters is typically oxidized anaerobically by sulfate. To explain the observations we used a numerical transport-reaction model that was constrained by the field observations. The model suggests that methane in the upper sediments is produced in the sulfate reduction zone at rates ranging between 0.012 and 31 mmol m−2 d−1, concurrent with sulfate reduction rates between 1.1 and 24 mmol SO42− m−2 d−1. These processes are supported by high organic matter content in the sediment and the use of non-competitive substrates by methanogenic microorganisms. Indeed sediment slurry incubation experiments show that non-competitive substrates such as trimethylamine (TMA) and methanol can be utilized for microbial methanogenesis at the study sites. The model also indicates that a significant fraction of methane is transported to the sulfate reduction zone from deeper zones within the sedimentary column by rising bubbles and gas dissolution. The shallow depths of methane production and the fast rising methane gas bubbles reduce the likelihood for oxidation, thereby allowing a large fraction of the methane formed in the sediments to escape to the overlying water column.
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Friedrich, Michael W., Dirk Schmitt-Wagner, Tillmann Lueders, and Andreas Brune. "Axial Differences in Community Structure ofCrenarchaeota and Euryarchaeota in the Highly Compartmentalized Gut of the Soil-Feeding TermiteCubitermes orthognathus." Applied and Environmental Microbiology 67, no. 10 (October 1, 2001): 4880–90. http://dx.doi.org/10.1128/aem.67.10.4880-4890.2001.
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ABSTRACT Methanogenesis represents an important electron sink reaction in the hindgut of soil-feeding termites. This is the first comprehensive analysis of the archaeal community structure within the highly compartmentalized intestinal tract of a humivorous insect, combining clonal analysis and terminal restriction fragment (T-RF) length polymorphism (T-RFLP) fingerprinting of the archaeal communities in the different gut compartments of Cubitermes orthognathus. We found that the morphological and physicochemical heterogeneity of the gut is reflected in a large phylogenetic diversity and pronounced axial differences in the composition of the archaeal gut microbiota, notably among those clones or ribotypes that could be assigned to methanogenic taxa. Comparative analysis of the relative frequencies of different archaeal lineages among the small-subunit rRNA gene (SSU rDNA) clones and their corresponding T-RF indicated that the archaeal community in the anterior, extremely alkaline hindgut compartment (P1) consists mainly of members of theMethanosarcinaceae, whereasMethanobacteriaceae andMethanomicrobiales predominate in the subsequent, more posterior compartments (P3/4a and P4b). The relative abundance ofThermoplasmales increased towards the rectum (P5). SSU rDNA sequences representing Crenarchaeota, which have not yet been reported to occur in the intestinal tracts of arthropods, were detected in all gut sections. We discuss how the spatial distribution of methanogenic populations may be linked to axial heterogeneity in the physicochemical gut conditions and to functional adaptations to their respective ecological niches.
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Kinnunen, Marta, Daniel Hilderbrandt, Stefan Grimberg, Shane Rogers, and Sumona Mondal. "Comparative study of methanogens in one- and two-stage anaerobic digester treating food waste." Renewable Agriculture and Food Systems 30, no. 6 (September 30, 2014): 515–23. http://dx.doi.org/10.1017/s1742170514000350.
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AbstractChanges in methanogenic archaea were investigated in pilot-scale experiments during one- and two-stage mesophilic anaerobic digestion (AD) of food waste. Methane yields were 379.7±75.3 liters of methane per kg of volatile solids [L-CH4(kg-VS)−1] added to the system, during one-stage operation, and 446±922 L-CH4(kg-VS)−1added during two-stage operation. Populations of methanogenic archaea were monitored quantitatively by targeting the functional gene for methyl-coenzyme-M reductase (mcrA) using real-time quantitative polymerase chain reaction techniques. During one-stage operation, meanmcrAgene concentrations were 2.48×109±2.7×109copies ml−1. Two-stage operation yielded meanmcrAgene concentrations of 9.85×108±8.2×108copies ml−1in the fermentation and 1.76×1010±8.5×109copies ml−1in the methanogenesis reactors, respectively. Diversity of archaea in the methanogenic reactors was investigated by denaturing gradient gel electrophoresis targeting the V3 region of 16S rRNA of archaea. The Shannon index (H) was 2.98 for one-stage operation and 7.29 for two-stage operation, suggesting greater archaeal diversity in the two-stage AD. The fivefold increase in methanogenic archaea populations during the two-stage operation, as indicated bymcrAgene concentration, corresponded to an increase in methane production rates. While the diversity may also be related to the stability of the microbial bioprocesses and improved methane production rates, the correlation between diversity and production rates should be studied further.
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Martin, William, and Michael J. Russell. "On the origin of biochemistry at an alkaline hydrothermal vent." Philosophical Transactions of the Royal Society B: Biological Sciences 362, no. 1486 (November 3, 2006): 1887–926. http://dx.doi.org/10.1098/rstb.2006.1881.
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A model for the origin of biochemistry at an alkaline hydrothermal vent has been developed that focuses on the acetyl-CoA (Wood–Ljungdahl) pathway of CO 2 fixation and central intermediary metabolism leading to the synthesis of the constituents of purines and pyrimidines. The idea that acetogenesis and methanogenesis were the ancestral forms of energy metabolism among the first free-living eubacteria and archaebacteria, respectively, stands in the foreground. The synthesis of formyl pterins, which are essential intermediates of the Wood–Ljungdahl pathway and purine biosynthesis, is found to confront early metabolic systems with steep bioenergetic demands that would appear to link some, but not all, steps of CO 2 reduction to geochemical processes in or on the Earth's crust. Inorganically catalysed prebiotic analogues of the core biochemical reactions involved in pterin-dependent methyl synthesis of the modern acetyl-CoA pathway are considered. The following compounds appear as probable candidates for central involvement in prebiotic chemistry: metal sulphides, formate, carbon monoxide, methyl sulphide, acetate, formyl phosphate, carboxy phosphate, carbamate, carbamoyl phosphate, acetyl thioesters, acetyl phosphate, possibly carbonyl sulphide and eventually pterins. Carbon might have entered early metabolism via reactions hardly different from those in the modern Wood–Ljungdahl pathway, the pyruvate synthase reaction and the incomplete reverse citric acid cycle. The key energy-rich intermediates were perhaps acetyl thioesters, with acetyl phosphate possibly serving as the universal metabolic energy currency prior to the origin of genes. Nitrogen might have entered metabolism as geochemical NH 3 via two routes: the synthesis of carbamoyl phosphate and reductive transaminations of α-keto acids. Together with intermediates of methyl synthesis, these two routes of nitrogen assimilation would directly supply all intermediates of modern purine and pyrimidine biosynthesis. Thermodynamic considerations related to formyl pterin synthesis suggest that the ability to harness a naturally pre-existing proton gradient at the vent–ocean interface via an ATPase is older than the ability to generate a proton gradient with chemistry that is specified by genes.
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Clayer, François, Yves Gélinas, André Tessier, and Charles Gobeil. "Mineralization of organic matter in boreal lake sediments: rates, pathways, and nature of the fermenting substrates." Biogeosciences 17, no. 18 (September 18, 2020): 4571–89. http://dx.doi.org/10.5194/bg-17-4571-2020.
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Abstract. The complexity of organic matter (OM) degradation mechanisms represents a significant challenge for developing biogeochemical models to quantify the role of aquatic sediments in the climate system. The common representation of OM by carbohydrates formulated as CH2O in models comes with the assumption that its degradation by fermentation produces equimolar amounts of methane (CH4) and dissolved inorganic carbon (DIC). To test the validity of this assumption, we modelled using reaction-transport equation vertical profiles of the concentration and isotopic composition (δ13C) of CH4 and DIC in the top 25 cm of the sediment column from two lake basins, one whose hypolimnion is perennially oxygenated and one with seasonal anoxia. Furthermore, we modelled solute porewater profiles reported in the literature for four other seasonally anoxic lake basins. A total of 17 independent porewater datasets are analyzed. CH4 and DIC production rates associated with methanogenesis at the five seasonally anoxic sites collectively show that the fermenting OM has a mean (± SD) carbon oxidation state (COS) value of -1.4±0.3. This value is much lower than the value of zero expected from carbohydrate fermentation. We conclude that carbohydrates do not adequately represent the fermenting OM in hypolimnetic sediments and propose to include the COS in the formulation of OM fermentation in models applied to lake sediments to better quantify sediment CH4 outflux. This study highlights the potential of mass balancing the products of OM mineralization to characterize labile substrates undergoing fermentation in sediments.
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Cai, Pingping, Zhuo Ning, Ningning Zhang, Min Zhang, Caijuan Guo, Manlan Niu, and Jiansheng Shi. "Insights into Biodegradation Related Metabolism in an Abnormally Low Dissolved Inorganic Carbon (DIC) Petroleum-Contaminated Aquifer by Metagenomics Analysis." Microorganisms 7, no. 10 (October 1, 2019): 412. http://dx.doi.org/10.3390/microorganisms7100412.
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In petroleum-contaminated aquifers, biodegradation is always associated with various types of microbial metabolism. It can be classified as autotrophic (such as methanogenic and other carbon fixation) and heterotrophic (such as nitrate/sulfate reduction and hydrocarbon consumption) metabolism. For each metabolic type, there are several key genes encoding the reaction enzymes, which can be identified by metagenomics analysis. Based on this principle, in an abnormally low dissolved inorganic carbon (DIC) petroleum-contaminated aquifer in North China, nine groundwater samples were collected along the groundwater flow, and metagenomics analysis was used to discover biodegradation related metabolism by key genes. The major new finding is that autotrophic metabolism was revealed, and, more usefully, we attempt to explain the reasons for abnormally low DIC. The results show that the methanogenesis gene, Mcr, was undetected but more carbon fixation genes than nitrate reduction and sulfate genes were found. This suggests that there may be a considerable number of autotrophic microorganisms that cause the phenomenon of low concentration of dissolved inorganic carbon in contaminated areas. The metagenomics data also revealed that most heterotrophic, sulfate, and nitrate reduction genes in the aquifer were assimilatory sulfate and dissimilatory nitrate reduction genes. Although there was limited dissolved oxygen, aerobic degrading genes AlkB and Cdo were more abundant than anaerobic degrading genes AssA and BssA. The metagenomics information can enrich our microorganic knowledge about petroleum-contaminated aquifers and provide basic data for further bioremediation.
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Mizuno, O., Y. Y. Li, and T. Noike. "Effects of sulfate concentration and sludge retention time on the interaction between methane production and sulfate reduction for butyrate." Water Science and Technology 30, no. 8 (October 1, 1994): 45–54. http://dx.doi.org/10.2166/wst.1994.0378.
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The effects of sulfate concentration and COD/S ratio on the anaerobic degradation of butyrate were investigated by using 2.0 L anaerobic chemostat-type reactor at 35°C. The study was conducted over a wide range of the COD/S ratio (1.5 to 148) by varying COD concentrations (2500–10000 mg/L) and sulfate concentrations (68–1667 mg-S/L) in the substrate. The sludge retention time at each COD/S ratio was changed from 5 to 20 days. The interaction between methane producing bacteria (MPB) and sulfate-reducing bacteria (SRB) was evidently influenced by COD/S ratio in the substrate. When COD/S ratio was 6.0 or more, methane production was the predominate reaction and over 80% of the total electron flow was used by MPB. At the COD/S ratio of 1.5, SRB utilzed over 50% of the total electron flow. A large amount of sulfate reduction resulted in not only the decrease of methane production, but also the rapid increase of the bacterial growth. The degradation pathway of butyrate and the composition of bacterial populations in the reactor were also dominated by COD/S ratio. In sulfate depleted condition, butyrate was degraded to methane via acetate and hydrogen by MPB. On the other hand, butyrate was firstly degraded into sulfide and acetate in sulfate rich conditions by SRB, and the produced acetate was then degraded by acetate consuming MPB and SRB. The methanogenesis from acetate was inhibited by the high concentration of sulfide.
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Thiel, Joana, James M. Byrne, Andreas Kappler, Bernhard Schink, and Michael Pester. "Pyrite formation from FeS and H2S is mediated through microbial redox activity." Proceedings of the National Academy of Sciences 116, no. 14 (March 18, 2019): 6897–902. http://dx.doi.org/10.1073/pnas.1814412116.
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The exergonic reaction of FeS with H2S to form FeS2(pyrite) and H2was postulated to have operated as an early form of energy metabolism on primordial Earth. Since the Archean, sedimentary pyrite formation has played a major role in the global iron and sulfur cycles, with direct impact on the redox chemistry of the atmosphere. However, the mechanism of sedimentary pyrite formation is still being debated. We present microbial enrichment cultures which grew with FeS, H2S, and CO2as their sole substrates to produce FeS2and CH4. Cultures grew over periods of 3 to 8 mo to cell densities of up to 2 to 9 × 106cells per mL−1. Transformation of FeS with H2S to FeS2was followed by57Fe Mössbauer spectroscopy and showed a clear biological temperature profile with maximum activity at 28 °C and decreasing activities toward 4 °C and 60 °C. CH4was formed concomitantly with FeS2and exhibited the same temperature dependence. Addition of either penicillin or 2-bromoethanesulfonate inhibited both FeS2and CH4production, indicating a coupling of overall pyrite formation to methanogenesis. This hypothesis was supported by a 16S rRNA gene-based phylogenetic analysis, which identified at least one archaeal and five bacterial species. The archaeon was closely related to the hydrogenotrophic methanogenMethanospirillum stamsii, while the bacteria were most closely related to sulfate-reducing Deltaproteobacteria, as well as uncultured Firmicutes and Actinobacteria. Our results show that pyrite formation can be mediated at ambient temperature through a microbially catalyzed redox process, which may serve as a model for a postulated primordial iron−sulfur world.
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Buan, Nicole R., Kimberly Rehfeld, and Jorge C. Escalante-Semerena. "Studies of the CobA-Type ATP:Co(I)rrinoid Adenosyltransferase Enzyme of Methanosarcina mazei Strain Gö1." Journal of Bacteriology 188, no. 10 (May 15, 2006): 3543–50. http://dx.doi.org/10.1128/jb.188.10.3543-3550.2006.
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ABSTRACT Although methanogenic archaea use B12 extensively as a methyl carrier for methanogenesis, little is known about B12 metabolism in these prokaryotes or any other archaea. To improve our understanding of how B12 metabolism differs between bacteria and archaea, the gene encoding the ATP:co(I)rrinoid adenosyltransferase in Methanosarcina mazei strain Gö1 (open reading frame MM3138, referred to as cobAMm here) was cloned and used to restore coenzyme B12 synthesis in a Salmonella enterica strain lacking the housekeeping CobA enzyme. cobAMm protein was purified and its initial biochemical analysis performed. In vitro, the activity is enhanced 2.5-fold by the addition of Ca2+ ions, but the activity was not enhanced by Mg2+ and, unlike the S. enterica CobA enzyme, it was >50% inhibited by Mn2+. The CobA Mm enzyme had a Km ATP of 3 μM and a Km HOCbl of 1 μM. Unlike the S. enterica enzyme, CobA Mm used cobalamin (Cbl) as a substrate better than cobinamide (Cbi; a Cbl precursor); the β phosphate of ATP was required for binding to the enzyme. A striking difference between CobA Se and CobA Mm was the use of ADP as a substrate by CobA Mm , suggesting an important role for the γ phosphate of ATP in binding. The results from 31P-nuclear magnetic resonance spectroscopy experiments showed that triphosphate (PPPi) is the reaction by-product; no cleavage of PPPi was observed, and the enzyme was only slightly inhibited by pyrophosphate (PPi). The data suggested substantial variations in ATP binding and probably corrinoid binding between CobA Se and CobA Mm enzymes.
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Kufka, Dominika, Michał Bucha, Łukasz Pleśniak, and Mariusz Orion Jędrysek. "Stable isotopes of C and H in methane fermentation of agriculture substrates at different temperature conditions." Open Geosciences 11, no. 1 (October 1, 2019): 471–81. http://dx.doi.org/10.1515/geo-2019-0039.
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AbstractAgricultural substrates (maize silage and cattle manure) were used to carry out methane fermentation process in bioreactors under laboratory conditions. Identical mixtures of these substrates were incubated for 43 days at 20, 30 and 40ºC to determine how different temperature conditions affect the δ13C(CH4), δH(CH4), and δ13C(CO2) values. To ensure correct anaerobic digestion, the following parameters of the organic substrates and fermentation solutions were monitored: total organic carbon (TOC), volatile solids (VS), volatile fatty acids (VFA), chemical oxygen demand (COD) and carbon to nitrogen ratio (C/N). The variants with higher incubation temperature yielded higher amounts of biogas (20ºC=84.5, 30ºC=101.8 and 40ºC=133.3 dm3/kg VS). In the case of gas products of methane fermentation, it was observed that the higher temperature of incubation affects the depletion in heavy isotopes. At 20ºC, 30ºC, and 40ºC mean values of δ13C(CH4) reached −26.4, −29.7, and −35.4‰, respectively. Mean values of δ2H(CH4) were −311.6, −354.0, and −398.5permil, and of δ13C(CO2) +8.9, +3.7, and −2.3‰, respectively. Moreover, the apparent fractionation coefficient α13C(CO2-CH4) were calculated, which decreased when the temperature increased. This isotopic tool was used to identify acetoclastic reaction as a dominant methanogenesis pathway. Observed changes in the isotopic composition of gaseous products obtained at different incubation temperatures may indicate decomposition of different carbon sources (e.g. lactate, propionate) to acetate and its fermentation by acetoclastic methanogens. It is possible that this was also related to the observation of the various metabolic models due to the varied methanogenic community composition.
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Hegarty, R. S. "Mechanisms for competitively reducing ruminal methanogenesis." Australian Journal of Agricultural Research 50, no. 8 (1999): 1299. http://dx.doi.org/10.1071/ar99007.
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Methane production is the principal end use of hydrogen gas derived by phosphoroclastic reactions or the release of protons from reducing equivalents by hydrogenases in the rumen. It should therefore be possible to reduce methanogenesis by (1) inhibiting H2 liberating reactions, (2) promoting alternative reactions which accept H+ during reoxidation of reducing equivalents, and (3) promoting alternative H2-using reactions. Strategies to reduce methanogenesis by these means are discussed. Particular attention is given to increasing synthesis of propionate and long chain fatty acids in the rumen, to acetogenesis, and to the actions of chemicals such as monensin and dietary fatty acids.