Discovering novel enzymes y functional screening of plurigenomic libraries from alga-associated Flavobacteriia and Gammaproteobacteria

Alga-associated microorganisms, in the context of their numerous interactions with the host and thecomplexity of the marine environment, are known to produce diverse hydrolytic enzymes with originalbiochemistry. We recently isolated several macroalgal-polysaccharide-degrading bacteria from the sur-face of the brown alga Ascophyllum nodosum. These active isolates belong to two classes: the Flavobacteriiaand the Gammaproteobacteria. In the present study, we constructed two “plurigenomic” (with multi-ple bacterial genomes) libraries with the 5 most interesting isolates (regarding their phylogeny andtheir enzymatic activities) of each class (Fv and Gm libraries). Both libraries were screened for diversehydrolytic activities. Five activities, out of the 48 previously identified in the natural polysaccharolyticisolates, were recovered by functional screening: a xylanase (GmXyl7), a beta-glucosidase (GmBg1), anesterase (GmEst7) and two iota-carrageenases (Fvi2.5 and Gmi1.3). We discuss here the potential role ofthe used host-cell, the average DNA insert-sizes and the used restriction enzymes on the divergent screen-ing yields obtained for both libraries and get deeper inside the “great screen anomaly”. Interestingly, thediscovered esterase probably stands for a novel family of homoserine o-acetyltransferase-like-esterases,while the two iota-carrageenases represent new members of the poorly known GH82 family (contain-ing only 19 proteins since its description in 2000). These original results demonstrate the efficiencyof our uncommon “plurigenomic” library approach and the underexplored potential of alga-associatedcultivable microbiota for the identification of novel and algal-specific enzymes.