Littérature scientifique sur le sujet « Red agarophyte alga »

Gelidium corneum is a species of red algae notable for its commercial important as an agarophyte in Morocco. Several regions from the Moroccan Atlantic show that this alga is an endangered species due to the excessive tearing. Hence, the repopulation of these areas is necessary. The in vitro culture of the species was carried out in three media: enriched seawater medium (PES medium (Provasoli Enriched Seawater, Provasoli 1968)), medium with seawater (SW) and medium with artificial seawater, with the addition of polyamines (putrescine (put), spermidine (spd), and spermine (spr)) as a growth regulator in the three media. The results obtained are very significant, especially in PES medium with a growth rate of 95%. Rhizoid formation and attachment of explants have been noted, especially in PES + Put medium.

Gelidium corneum (syn. sesquipedale) is an industrially and ecologically important species of red alga used for the production of high-quality agar. However, the species is also of growing interest for the production of other valuable compounds, such as mycosporine-like amino acids (MAAs), with potential cosmeceutical and biomedical applications. Novel methods using two pulsed power techniques, high-voltage electrical discharges (HVED) and pulsed electrical fields (PEF), were evaluated for efficacy of MAA extraction. Algal suspensions were prepared at two ratios (1:20 and 1:40 w:v). Four different extraction protocols were compared: (i) high-voltage electrical discharges, (ii) pulsed electric fields, (iii) maceration at room temperature, and (iv) maceration at 50 °C. The algae were treated in three states: freshly harvested, dried, and powdered. HVED and PEF treatments were effective when performed on fresh algae, and in particular the HVED treatment resulted in yields of MAAs twenty times higher than the control: 0.81 ± 0.05 mg/gDry Weight (DW) vs. 0.037 ± 0.002 mg/gDW. This effect was not observed to the same extent when the algae were dried or powdered, although HVED remained the most selective method overall.

Gracilaria species are an important source of agar. The South African Gracilaria industry has experienced a number of setbacks over the last decade in the form of complete or partial die-offs of the agarophyte growing in Saldanha Bay, which may be attributed to bacterial infection. Since a positive correlation was observed between the presence of agarolytic epiphytes and bacterial pathogenicity, we investigated the role of an agarase in the virulence mechanism employed by a bacterium that elicits disease in Gracilaria gracilis. The recombinant plasmid pDA1, isolated from a Pseudoalteromonas gracilis B9 genomic library, was responsible for the agarolytic activity exhibited by Escherichia coli transformants when grown on solid medium. A blast search of the GenBank database showed that an 873 bp ORF (aagA) located on pDA1 had 85 % identity to the β-agarase (dagA) from Pseudoalteromonas atlantica ATCC 19262T (or IAM 12927T) at the amino acid level. AagA was purified from the extracellular medium of an E. coli transformant harbouring pDA1 by using a combination of gel filtration and ion-exchange chromatography. AagA has an M r of 30 000 on SDS-PAGE. TLC of the digestion products of AagA showed that the enzyme cleaves the β-(1,4) linkages of agarose to yield predominately neoagarotetraose. Western hybridization confirmed that the cloned agarase was in fact the extracellular β-agarase of P. gracilis B9. The observed relationship between disease symptoms of G. gracilis and the agarolytic phenotype of P. gracilis B9 was confirmed. Transmission electron microscope examination of cross sections of both healthy G. gracilis and G. gracilis infected with P. gracilis, revealed a weakening of the cell structure in the latter plants. Immunogold-labelled antibodies localized the agarase in situ to the cell walls of bleached G. gracilis. Thus, the weakening observed in the cell structure of G. gracilis infected with P. gracilis can be attributed to degradation of the mucilaginous component of the cell wall of the bleached thalli.

The red macroalga Agarophyton chilensis is a well-known producer of eicosanoids such as hydroxyeicosatetraenoic acids, but the alga produces almost no prostaglandins, unlike the closely related A. vermiculophyllum. This indicates that the related two algae would have different enzyme systems or substrate composition. To carry out more in-depth discussions on the metabolic pathway of eicosanoids between the two algae, we investigated the characteristics of glycerolipids, which are the substrates of eicosanoids production, of A. chilensis and compared them to the reported values of A. vermiculophyllum. In A. chilensis, monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), sulfoquinovosyldiacylglycerol (SQDG), and phosphatidylcholine (PC) were the major lipid classes and accounted for 44.4% of the total lipid extract. The predominant fatty acids were arachidonic acid (20:4n-6), an eicosanoids precursor, and palmitic acid (16:0). The 20:4n-6 content was extremely high in MGDG and PC (>70%), and the 16:0 content was extremely high in DGDG and SQDG (>40%). A chiral-phase HPLC analysis showed that fatty acids were esterified at the sn-1 and sn-2 positions of those lipids. The glycerolipid molecular species were determined by reversed-phase HPLC–ESI–MS analysis. The main glycerolipid molecular species were 20:4n-6/20:4n-6 (sn-1/sn-2) for MGDG (63.8%) and PC (48.2%), 20:4n-6/16:0 for DGDG (71.1%) and SQDG (29.4%). These lipid characteristics of A. chilensis were almost the same as those of A. vermiculophyllum. Hence, the differences of the eicosanoids producing ability between the two algae would not be due to the difference of substrate composition but the difference of enzyme system.

The family 117 glycoside hydrolase (GH117) enzymes have exo-α-1,3-(3,6-anhydro)-L-galactosidase activity, removing terminal nonreducing α-1,3-linked 3,6-anhydro-L-galactose residues from their red algal neoagarose substrate. These enzymes have previously been phylogenetically divided into clades, and only the clade A enzymes have been experimentally studied to date. The investigation of two GH117 enzymes, Zg3615 and Zg3597, produced by the marine bacteriumZobellia galactanivoransreveals structural, biochemical and further phylogenetic diversity between clades. A product complex with the unusual β-3,6-anhydro-L-galactose residue sheds light on the inverting catalytic mechanism of the GH117 enzymes as well as the structure of this unique sugar produced by hydrolysis of the agarophyte red algal cell wall.

Terrestrial plants are known to “garden” the microbiota of their rhizosphere via released metabolites (that can attract beneficial microbes and deter pathogenic microbes). Such a “gardening” capacity is also known to be dynamic in plants. Although microbial “gardening” has been recently demonstrated for seaweeds, we do not know whether this capacity is a dynamic property in any aquatic flora like in terrestrial plants. Here, we tested the dynamic microbial “gardening” capacity of seaweeds using the model invasive red seaweed Agarophyton vermiculophyllum. Following an initial extraction of surface-associated metabolites (immediately after field collection), we conducted a long-term mesocosm experiment for 5 months to test the effect of two different salinities (low = 8.5 and medium = 16.5) on the microbial “gardening” capacity of the alga over time. We tested “gardening” capacity of A. vermiculophyllum originating from two different salinity levels (after 5 months treatments) in settlement assays against three disease causing pathogenic bacteria and seven protective bacteria. We also compared the capacity of the alga with field-collected samples. Abiotic factors like low salinity significantly increased the capacity of the alga to deter colonization by pathogenic bacteria while medium salinity significantly decreased the capacity of the alga over time when compared to field-collected samples. However, capacity to attract beneficial bacteria significantly decreased at both tested salinity levels when compared to field-collected samples. Dynamic microbial “gardening” capacity of a seaweed to attract beneficial bacteria and deter pathogenic bacteria is demonstrated for the first time. Such a dynamic capacity as found in the current study could also be applicable to other aquatic host–microbe interactions. Our results may provide an attractive direction of research towards manipulation of salinity and other abiotic factors leading to better defended A. vermiculophyllum towards pathogenic bacteria thereby enhancing sustained production of healthy A. vermiculophyllum in farms.

AbstractAgarophyton vermiculophyllum is a commercially important red alga for agar production in the Northwest Pacific Ocean and is an invasive seaweed in Europe. High temperature is an important environmental stressor that influences its growth, metabolism, and migration. Nevertheless, little is known about the molecular mechanisms underpinning the response of A. vermiculophyllum to heat stress. Using RNA-sequencing, we performed the first comprehensive transcriptome analysis of A. vermiculophyllum under heat stress to explore and identify potentially important heat stress-responsive genes. After de novo assembly of the transcriptome, 55,486 unigenes were found, of which 39,687 unigenes (71.52%) were functionally annotated. In total, 2,923 differentially expressed genes (DEGs) were detected between heat-stressed and control samples. Heat shock proteins represented the most abundant DEGs. Transcript factors were also significantly differently expressed under heat stress. Meanwhile, the photoprotective mechanism based on PsbS (Photosystem II subunit S) related nonphotochemical quenching and PGR5 (proton gradient regulation 5) dependent cyclic electron flow around photosystem I was found to be promoted under heat stress, which may help A. vermiculophyllum to cope with the high temperature. This study lays an important foundation for further elucidation of the molecular mechanism underlying heat tolerance in A. vermiculophyllum.

Les co-produits industriels de la première étape d’extraction d’agar (de l’algue rouge Gelidium sesquipedale) constituent au sein de l’entreprise SETEXAM des volumes importants potentiellement valorisables. L’objectif de ce travail est de démontrer qu’ils peuvent être utilisés en tant qu‘éliciteur, ou stimulateur des défenses naturelles (SDN). D’abord, la composition élémentaire du co-produit alcalin a révélé une teneur en minéraux de 44 % (Na, K éléments majeurs) avec des traces de métaux lourds, mais en dessous de la limite autorisée. Les principaux composés organiques détectés sont des glucides (12,5 %) et une fraction riche en floridoside a été obtenue. Ce composé a été identifié par une méthode originale, la CPG-MS. Le co-produit alcalin, recyclé au cours du procédé industriel, voit sa teneur en glucides diminuer avec l’augmentation du nombre de cycles. Ces co-produits, appliqués sur des plants de tomates cultivées en serre sous stress biotique, sont capables de stimuler des réponses de défense (activités enzymatiques, expression des gènes). La dose optimale (50 mg.L-1) a été déterminée ainsi que les conditions d’applications et la durée d’activation des réponses. En plein champ, les co-produits ont été testés sur vigne et sur tomate, pour leur capacité à réduire les symptômes du mildiou, ou de la cladosporiose. Des résultats prometteurs ont été obtenus comparés à des éliciteurs déjà commercialisés, en conditions de pression modérée. Le co-produit issu de la première étape d’extraction industrielle d’agar a montré une activité comme SDN et peut constituer une solution de protection des cultures permettant une réduction des pesticides pour une agriculture durable et plus respectueuse de l’environnement. Ce travail constitue une base pour un dossier d’homologation du produit qui transformerait ces co-produits de coût en ressource pour l’entreprise
The industrial by-products of the first step of agar extraction (from red alga Gelidium sesquipedale) constitute large volumes at SETEXAM company that might be valorized. The objective of this work is to prove that they can be used as elicitor, or plant defense stimulator (PDS). Firstly, the elemental composition of the alkaline by-product revealed a mineral content of 44% (Na, K major components) with heavy metal traces, but under authorized limits. The principal organic components detected are carbohydrates (12.5%) and a fraction rich in floridoside was obtained. This molecule was identified with an original method, through GC-MS. The alkaline by-product, recycled through the industrial process, has its carbohydrate content diminished as the number of cycles increases. These by-products, applied on tomato plants grown in greenhouse under biotic stress, are capable of stimulating defense responses (enzymatic activities, gene expression). The optimal dose (50 mg.L-1) was determined together with the application conditions and time span of responses. In field, the by-products were tested on grapevine and on tomato, for their capacity to reduce downy mildew, or leaf mold symptoms. Promising results were obtained compared to already commercialized elicitors, for moderate disease pressure. The by-product obtained from the first step of industrial agar extraction showed a PDS activity and can be a solution for culture defense allowing a reduction of pesticides for a durable and environmentally friendly agriculture. This work is a base for a homologation file of the product that would transform these by-products from cost to resource for the company