Academic literature on the topic 'Xylene – Biodegradation'

ABSTRACT The soil fungus Cladophialophora sp. strain T1 (= ATCC MYA-2335) was capable of growth on a model water-soluble fraction of gasoline that contained all six BTEX components (benzene, toluene, ethylbenzene, and the xylene isomers). Benzene was not metabolized, but the alkylated benzenes (toluene, ethylbenzene, and xylenes) were degraded by a combination of assimilation and cometabolism. Toluene and ethylbenzene were used as sources of carbon and energy, whereas the xylenes were cometabolized to different extents. o-Xylene and m-xylene were converted to phthalates as end metabolites; p-xylene was not degraded in complex BTEX mixtures but, in combination with toluene, appeared to be mineralized. The metabolic profiles and the inhibitory nature of the substrate interactions indicated that toluene, ethylbenzene, and xylene were degraded at the side chain by the same monooxygenase enzyme. Our findings suggest that soil fungi could contribute significantly to bioremediation of BTEX pollution.

The biodegradation kinetics of BTE-oX and MTBE, mixed all together, in the presence of 905mg/L VSS of BTEX-acclimated biomass was evaluated. Effects of soil and Tergitol NP-10 in aqueous samples on substrate biodegradation rates were also evaluated. Biodegradation kinetics was evaluated for 36 hours, every 6 hours. MTBE biodegradation followed a first-order one-phase kinetic model in all samples, whereas benzene, toluene and ethylbenzene biodegradation followed a first-order two-phase kinetic model in all samples. O-xylene biodegradation followed a first-order two-phase kinetic model in the presence of biomass only. Interestingly, o-xylene biodegradation was able to switch to a first-order one-phase kinetic model when either soil or soil and Tergitol NP-10 were added. The presence of soil in aqueous samples retarded benzene, toluene and ethylbenzene removal rates. O-xylene and MTBE removal rates were enhanced by soil. The addition of Tergitol NP-10 to aqueous samples containing soil had a positive effect on substrate removal rate in all samples. Substrate percent removals ranged 77–99.8% for benzene, toluene and ethylbenzene. O-xylene and MTBE percent removals ranged 50.1–65.3% and 9.9–43.0%, respectively.

Strain mX was isolated from a petrol-contaminated soil, after enrichment on minimal medium with 0.5% (v/v) meta-xylene as a sole carbon source. The strain was tentatively characterized as Pseudomonas putida and harboured a large plasmid (pMX) containing xyl genes involved in toluene or meta-xylene degradation pathways via an alkyl monooxygenase and a catechol 2,3-dioxygenase. This new TOL-like plasmid was stable over two hundred generations and was self-transferable. After conjugal transfer to P. putida F1, which possesses the Tod chromosomal toluene biodegradative pathway, the transconjugant P. putida F1(pMX) was able to grow on benzene, toluene, meta-xylene, para-xylene, and ethylbenzene compounds as the sole carbon sources. Catechol 2,3-dioxygenases of the transconjugant cells presented a more relaxed substrate specificity than those of parental cells (strain mX and P. putida F1).Key words: biodegradation, conjugative transfer, toluene, xylene, Pseudomonas.

The biodegradation kinetics of BTE-oX and MTBE, mixed all together, in the presence of bioaugmented bacterial populations as high as 880 mg/L VSS was evaluated. The effect of soil in aqueous samples and the effect of Tergitol NP-10 on substrate biodegradation rates were also evaluated. Biodegradation kinetics was evaluated for 36 hours, every 6 hours. Benzene and o-xylene biodegradation followed a first-order one-phase kinetic model, whereas toluene and ethylbenzene biodegradation was well described by a first-order two-phase kinetic model in all samples. MTBE followed a zero-order removal kinetic model in all samples. The presence of soil in aqueous samples retarded BTE-oX removal rates, with the highest negative effect on o-xylene. The presence of soil enhanced MTBE removal rate. The addition of Tergitol NP-10 to aqueous samples containing soil had a positive effect on substrate removal rate in all samples. Substrate percent removals ranged from 95.4-99.7% for benzene, toluene and ethylbenzene. O-xylene and MTBE percent removals ranged from 55.9-90.1% and 15.6-30.1%, respectively.

Diesel, toluene and naphthalene-degrading microbial consortia were isolated from a diesel-contaminated soil. The presence of catabolic genes, xylE and ndoB responsible for toluene/xylene and naphthalene biodegradation, respectively, were screened by PCR techniques in all microbial consortia. The diesel-consortium possessed both catabolic genes, the toluene-consortium only the xylE gene, while the naphthalene-consortium possessed only the ndoB gene. On the basis of these results, it was concluded that contaminated soil has indigenous microbes with a high natural potential for biodegradation.

An experimental strategy is introduced for studying the biodegradation of wastewaters containing volatile contaminants using an alternating anoxic/microaerobic sequencing batch reactor (SBR). Benzene, toluene, and the xylene isomers (BTX) served as model volatile contaminants for this study. The reactor was configured to overcome stripping the volatile BTX compounds into the atmosphere to provide opportunities for BTX biodegradation. Oxygen-free anoxic and microaerobic (< 0.2 mg/L dissolved oxygen) conditions were established using a novel laboratory reactor configuration. ORP was successfully used to monitor different electron acceptor conditions in the SBR. Toluene and m-xylene were amenable to anoxic (denitrifying) metabolism while benzene, o-, and p-xylene were biodegradable under microaerobic conditions. The results demonstrate that establishing microaerobic conditions in full-scale bioreactors may be an appropriate way to encourage the biodegradation of aerobically biodegradable volatile contaminants. Additionally, the laboratory reactor configuration introduced in this paper may be useful in subsequent studies involving microaerobic metabolism.

BTEX removal under aerobic conditions by unleaded gasoline acclimated biomass and BTEX acclimated biomass, and the effect of surfactant on BTEX biodegradation were evaluated. The effect of BTEX concentration as the sole source of carbon for biomass acclimation and the effect of yeast extract on cell growth in unleaded gasoline-fed reactors were also evaluated. For the unleaded gasoline acclimated biomass, benzene was shown the most recalcitrant among all BTEX, followed by o-xylene and toluene with 16–23%, 35–41% and 57–69% biodegradation, respectively. Ethylbenzene was consistently the fastest BTEX chemical removed with 99% biodegradation for the four bioreactor acclimated biomasses tested. For the 1,200 ppm BTEX acclimated biomass, benzene showed the highest removal efficiency (99%) among the four biomass environmental conditions tested, along with 99% toluene and 99% ethylbenzene biodegradation. O-xylene showed 92–94% removal. In all bioassays tested Tergitol NP-10 was fully removed, and did not have a substantial effect on BTEX biodegradation at the end of a 10-day evaluation.

ABSTRACT Two strains, identified as Rhodococcus wratislaviensis IFP 2016 and Rhodococcus aetherivorans IFP 2017, were isolated from a microbial consortium that degraded 15 petroleum compounds or additives when provided in a mixture containing 16 compounds (benzene, toluene, ethylbenzene, m-xylene, p-xylene, o-xylene, octane, hexadecane, 2,2,4-trimethylpentane [isooctane], cyclohexane, cyclohexanol, naphthalene, methyl tert-butyl ether [MTBE], ethyl tert-butyl ether [ETBE], tert-butyl alcohol [TBA], and 2-ethylhexyl nitrate [2-EHN]). The strains had broad degradation capacities toward the compounds, including the more recalcitrant ones, MTBE, ETBE, isooctane, cyclohexane, and 2-EHN. R. wratislaviensis IFP 2016 degraded and mineralized to different extents 11 of the compounds when provided individually, sometimes requiring 2,2,4,4,6,8,8-heptamethylnonane (HMN) as a cosolvent. R. aetherivorans IFP 2017 degraded a reduced spectrum of substrates. The coculture of the two strains degraded completely 13 compounds, isooctane and 2-EHN were partially degraded (30% and 73%, respectively), and only TBA was not degraded. Significant MTBE and ETBE degradation rates, 14.3 and 116.1 μmol of ether degraded h−1 g−1 (dry weight), respectively, were measured for R. aetherivorans IFP 2017. The presence of benzene, toluene, ethylbenzene, and xylenes (BTEXs) had a detrimental effect on ETBE and MTBE biodegradation, whereas octane had a positive effect on the MTBE biodegradation by R. wratislaviensis IFP 2016. BTEXs had either beneficial or detrimental effects on their own degradation by R. wratislaviensis IFP 2016. Potential genes involved in hydrocarbon degradation in the two strains were identified and partially sequenced.

The microbial ecology and potential for biodegradation of benzene, toluene, ethylbenzene, and o- and m-xylene (BTEX) in core materials contaminated with unleaded gasoline were investigated. The site studied was unique because a portion of the contaminated area was biostimulated in a demonstration of the use of hydrogen peroxide as an oxygen source in in situ biorestoration. Two years after termination of the field demonstration, core samples were collected from uncontaminated, contaminated, and biostimulated areas at the site and analyzed for inorganic nutrients, microbial numbers, mineralization potential of glucose, benzene, and toluene using liquid scintillation counting, and biotransformation of BTEX using gas chromatography. The results indicated that the subsurface microflora at the site was active and capable of degrading a variety of compounds. Microbial numbers and contaminant biodegradation potential in samples from the biostimulated area were greater than in uncontaminated and contaminated zones. Toluene, ethylbenzene, and m-xylene were removed in all core materials, whereas o-xylene was recalcitrant. Mineralization experiments indicated that toluene was mineralized to a greater extent than benzene. These data indicated that the biodegradation potential of the subsurface material from the biostimulated zone, which still contained residual hydrocarbon, remained enhanced for at least 2 yr after the in situ biorestoration process had been terminated.

The increased use of alcohols as gasoline additives, and possible substitutes, has prompted the investigation of the fate of gasoline/alcohol mixtures in the environment. In situ bioremediation is one technique that can successfully be applied to remove ground water contaminants particularly in situations where the adsorptive capacity of the soil plays a major role. Frequently, enhanced in situ bioremediation techniques rely on indigenous microorganisms to degrade ground water contaminants; this technique may sometimes include the addition of acclimated bacteria.

In this study, soil microcosms were constructed in order to simulate the conditions found in a saturated aerobic aquifer. The biodegradation potential of methanol, benzene, and m-xylene was investigated. Uncontaminated soil from the surface, 12, 16.5, and 18 foot depths was utilized to observe the differences in microbial responses throughout the soil profile. The biodegradation potential of the indigenous microbiota was determined and compared to that of benzene acclimated bacteria, for all the compounds in the mixture. To observe the impact that chemical and physical soil characteristics may have on microbial responses, soils from each depth were classified on the basis of their particle size, moisture content and pH.

Substantial methanol, benzene, and m-xylene biodegradation by the indigenous microorganisms occurred in all subsurface soils. While methanol was readily biodegradable over concentrations ranging from about 80 mg/L to about 200 mg/L, benzene inhibited methanol biodegradation at about 125 mg/L in all soil depths. The addition of benzene acclimated bacteria considerably increased the biodegradation rates of all compounds in the mixture. Such increases in biodegradation rates may be attributed to the activities of both groups, the indigenous microorganisms and the benzene acclimated bacteria. The results obtained by this study suggest that biodegradation of methanol, benzene, and m-xylene can readily occur in a saturated aerobic subsurface environment. The physical and chemical properties of a ground water aquifer seem to have a marked effect on microbial responses, and consequently on the biodegradation potential of water contaminants.

Master of Science

Microcosm studies were conducted beginning with three xylene isomers: ortho-xylene, meta-xylene and para-xylene; and continued with the four mononitroxylene (MNX) isomers, culminating with testing ten dinitroxylene (DNX) isomers. Soil samples were obtained from a historically contaminated site with high levels of dinitrotoluene (DNT), trinitrotoluene (TNT) and dinitroxylene (DNX) and used as the inoculum for microcosm tests. The microcosm method of different isomers was based on the previous work on biodegradation of nitrotoluene. As it was demonstrated previously that 2,4-DNT degrading bacteria were present at the site, it was hypothesized that these may be capable of transforming or cometabolizing some of DNX isomers. Thus, DNX cometabolism studies were conducted in the presence of 2,4-DNT degrading bacteria. The presence of xylene and 2,4-DNT degrading was confirmed in this thesis. Meanwhile, several MNX and DNX isomers showed degradability in microcosm studies. Cometabolism studies showed that four DNX isomers could be cometabolized by 2,4-DNT enrichment.

Thesis (PhD)--Stellenbosch University, 2003.
ENGLISH ABSTRACT: Plant biomass, the most abundant renewable resource in nature, consists of matrices of mainly lignin, cellulose, hemicellulose as well as inorganic components. Xylan, the major hemicellulose component in plant cell walls, is the most abundant polysaccharide after cellulose. This makes the main constituent sugar of xylan, D-xylose, the second most abundant renewable monosaccharide in nature. Very few hemicelluloses are either homopolymeric or entirely linear. Therefore, the variety of enzymes involved in their hydrolysis is more complex than the enzyme group responsible for the hydrolysis of cellulose. Although the ability to degrade xylan is common among bacteria and filamentous fungi, this trait is relatively rare among yeasts. However, some strains of the yeast Pichia stipitis are, amongst others, able to degrade xylan. As P. stipitis is also one of the best D-xylose fermenting yeasts thus far described, this yeast has the potential of fermenting polymeric xylan directly to ethanol. However, it was shown that the natural xylanolytic ability of this yeast is very weak. In this study, xylanolytic genes were expressed in P. stipitis to test the ability of the yeast to produce heterologous proteins, and to determine the enhancement of xylan utilisation by the recombinant strain. The native xylose reductase gene (XYLl) and transketolase gene (TKL) and the heterologous Saccharomyces cerevisiae phosphoglycerate kinase (PGKl) gene promoter were cloned into P. stipitis transformation vectors and used to express the Trichoderma reesei ~-xylanase encoding gene (xyn2) as reporter gene. It was shown that the XYLl promoter was induced in the presence of D-xylose and that the TKL promoter was constitutively expressed. The PGKl promoter of S. cerevisiae did not function in P. stipitis . When the T reesei xyn2 gene and the Aspergillus kawachii ~-xylanase encoding gene (xynC) were expressed under control of the XYLl promoter, extracellular ~-xylanase activity of up to 136 nkat/ml and 171 nkatlml was observed, respectively. This activity declined over time due to the presence of extracellular proteases, secreted by P. stipitis. Growing the cultures in a fermentor and controlling the pH level to pH 6 did not alleviate the reduction of heterologous l3-xylanase activity. When the Aspergillus niger l3-xylosidase encoding gene (xlnD) was expressed as a fusion gene (designated XL02) with the S. cerevisiae mating factor secretion signal (MFal) under control of the P. stipitis TKL promoter, extracellular l3-xylosidase activity of 0.132 nkatlml was observed. Co-expression of the xyn2 and XL02 genes led to B-xylanase and l3-xylosidase activities of 128 nkatlml and 0.113 nkat/ml, respectively. Co-expression of the xynC and XL02 genes led to l3-xylanase and l3-xylosidase activities of 165 nkat/ml and 0.124 nkatlml, respectively. The expression of the fungal xylanolytic genes in P. stipitis also led to an increased biomass yield when the recombinant strains were cultured on birchwood xylan as sole carbon source. The strain co-expressing the A. kawachii l3-xylanase and A. niger l3-xylosidase encoding genes was the most successful, yielding a 3.2-fold higher biomass level than the control strain. Biomass levels of the recombinant strains were further improved on average by 85% by growing them in a fermentor under conditions of high oxygenation. The strains were also tested for direct conversion of xylan to ethanol and the strain co-expressing the A. kawachii l3-xylanase and A. niger l3-xylosidase encoding genes produced 1.35 giL ethanol, which represents a 3.6-fold increase in ethanol yield over the reference strain. These strains represent a step towards the efficient degradation and utilisation of hemicellulosic materials by ethanol-producing yeasts.
AFRIKAANSE OPSOMMING: Plant biomassa, die volopste hernubare koolstotbron in die natuur, bestaan uit matrikse van lignien, sellulose en hemisellulose. Xilaan, die hoof hemisellulose komponent in plantselwande, is na sellulose die volopste polisakkaried. Gevolglik is die hoof suikerkomponent van xilaan, naamlik D-xilose, die tweede volopste hernubare monosakkaried in die natuur. Baie min hemisellulose molekules is homopolimere of heeltemal linieêr. Daarom is die ensieme betrokke by die atbraak van hemiselluloses meer kompleks as die ensieme betrokke by die atbraak van sellulose. Bakterieë en filamentagtige fungi wat oor die vermoë om xilaan af te breek beskik, kom wydversprei voor maar relatief min giste kan xilaan benut. Sommige rasse van die gisspesie Pichia stipitis het egter beperkte vermoë om xilaan af te breek. P. stipitis is ook een van die beste D-xilose fermenterende giste wat tot dusver beskryf is en het dus die potensiaalom etanol vanafpolimeriese xilaan te produseer. In hierdie studie is gene wat kodeer vir xilaanatbrekende ensieme in P. stipitis uitgedruk om die vermoë van die gis as heteroloë uitdrukking sisteem te evalueer. Verder is die effek van die heteroloë xilaanatbrekende ensieme tydens groei op xilaan as enigste koolstotbron getoets. Die promoters van die xilosereduktasegeen (XYLl), die transketolasegeen (TKL) van P. stipitis en die fosfogliseraatkinasegeen (PGKl) van Saccharomyces cerevisiae is in P. stipitis transformasie vektore gekloneer en gebruik om die Trichoderma reesei ~-xilanasegeen (xyn2) as verklikkergeen uit te druk. Dit het bewys dat die XYLI promotor induseerbaar is in die teenwoordigheid van D-xilose terwyl die TKL geen konstant uitgedruk was. Die PGKI promotor van S. cerevisiae was nie funksioneel in P. stipitis nie. Ekstrasellulêre ~-xilanase aktiwiteit van onderskeidelik 136 nkatlml en 171 nkatlml kon waargeneem word wanneer die T reesei xyn2 geen of die Aspergillus kawachii ~-xilanasegeen (xynC) onder beheer van die XYLI promotor uitgedruk is. Hierdie aktiwiteit het afgeneem na gelang van tyd a.g.v. die teenwoordigheid van ekstrasellulêre proteases wat deur P. stipitis uitgeskei word. Die afname van ekstrasellulêre ~-xilanase aktiwiteit kon nie voorkom word deur die kulture in 'n fermentor te groei en die pH vlak tot pH 6 te beheer nie. Tydens uitdrukking van die Aspergillus niger ~-xilosidase geen (xlnD) as 'n fusiegeen (genoem XL02) met die paringsfaktor sekresiesein (MFal) van S. cerevisiae onder transkripsionele beheer van die P. stipitis TKL promotor, kon ekstrasellulêre ~-xilosidase aktiwiteit van 0.132 nkatlml waargeneem word. Gesamentlike uitdrukking van die xyn2 en XL02 gene het gelei tot ~-xilanase en ~-xilosidase aktiwiteite van 128 nkatlml and 0.113 nkat/ml, onderskeidelik. Gesamentlike uitdrukking van die xynC en XL02 gene het gelei tot ~-xilanase en ~-xilosidase aktiwiteite van 165 nkatlml and 0.124 nkatlml, onderskeidelik. Die uitdrukking van xilaanatbrekende ensieme III P. stipitis het verhoogbe biomassaproduksie teweeg gebring wanneer die rekombinante gisrasse op birchwood xilaan as enigste koolstotbron gegroei het. Die rekombinante ras wat die A. kawachii ~-xilanasegeen en die A. niger ~-xilosidase geen gesamentlik uitdruk, was die mees suksesvolle ras en het 3.2-voudig hoër biomassa as die kontrole ras opgelewer. Die biomassa van die rekombinante rasse tydens groei op xilaan as enigste koolstotbron kon gemiddeld met 85% verhoog word deur die giste onder hoë suurstotkonsentrase in 'n fermentor te kweek. Die rekombinante rasse is verder ook getoets vir hul vermoë om xilaan direk tot etanol om te skakel. Die rekombinante ras wat die A. kawachii ~-xilanasegeen en die A. niger ~-xilosidase geen gesamentlik uitgedruk het, het 'n 3.6- voudige verhoging in etanolproduksie getoon en 1.35 gIL ethanol gelewer. Hierdie rekombinante gisrasse verteenwoordig 'n stap nader aan die doeltreffende atbraak en benutting van hemisellulose deur etanolproduserende giste.