Abstract :
[en] Algal polysaccharides are increasingly used in food industry for their gelling properties and in pharmacology for their therapeutic properties. Furthermore, increasingly interest is taken on algae for their use in the production of biofuels and bioenergies. To purify algal polysaccharides and degrade algal biomass, specific microbial enzymes are needed. Microorganisms living on algae are an interesting source of those enzymes, as they are in constant interaction with algal biomass.
The aim of our study is to identify new enzymes degrading algae, produced by microorganisms living on the surface of algae. Therefore we developed a method for microbial DNA extraction from biofilms living on brown algae (Ascophyllum nodosum). Microbial DNA was extracted, restricted and inserted in cultivable host cells of Echerichia coli, for the construction of our metagenomic DNA library. This metagenomic library was first screened, on solid media with specific substrates, for enzymes generally used in the degradation of biomass (lipases, cellulases, proteases, beta-glucosidases, alpha-amylases, arabinanases and xylanases). Five lipolytic enzymes, one beta-glucosidase and one cellulase were identified. Those enzymes show very low percentages of sequences identities with known enzymes, meaning we identified new and unknown enzymes. Those enzymes and their activity are being characterized. Preliminary tests show interesting results, like a cellulase active at low temperature. Screening tests are now being developed to identify enzymes hydrolyzing algal polysaccharides like agarases, carrageenases, alginate lyases, laminarinases,… Those enzymes aren’t well known yet and we hope to identify new enzymes (families) with our rich DNA library by our approach.
