Functional exploration of naturally and artificially enriched rumen microbiomes reveals novel enzymatic synergies involved in polysaccharide breakdown. Enriched rumen microbiomes

To face the structural complexity of plant cell wall, which compose their main carbon source forin the bovine ruminal ecosystem, rimunal bacteria have evolved sophisticated multi-functional enzyme complexes. In order to unveillock them from the vast world of uncultured bacteria, a high-throughput activity-based metagenomic approach was developed. In particular, a multi-step screening methodology was set-up to highlight identify metagenomic clones acting on polysaccharides and polyaromatic compounds, and to sort outhighligth those that are the most efficient to break down a highly lignifiedbiorefinary relevant industrial substrate, wheat straw . This approach was used to explore the functional potential of two different bovine ruminal microbiomes, totalizing 1.5 Gb, issued from in vivo and in vitro enrichments on wheat straw. 172 fosmid metagenomic clones were isolated, producing various original glycoside-hydrolases, esterases and oxidoreductases. In particular, 23 enzymes, mostly issued from unknown bacterial genera, harbour still uncharacterized structural modules. These novel enzymes present high potential for numerous biotechnological processes, as they are highly efficient, alone or acting synergistically, to break down crude plant cell wall extracts.