2-43: Targeted discovery of thermophilic microbial communities and enzymes that deconstruct lignocellulose in a high-solids environment via metagenomic analysis

There is a need for novel enzymes capable of deconstructing lignocellulosic biomass under the harsh conditions associated with industrial biofuel production, particularly thermophilic environments with little free water (high-solids) that contain feedstock-derived inhibitors.  In this work, solid-state cultures were performed to enrich for microbial communities capable of subsisting on ethanol-and-water-extracted rice straw under mesophilic (35 ˚C) and thermophilic (55 ˚C) conditions.  Metagenome sequencing was performed on enriched communities to determine community composition and mine for genes encoding lignocellulolytic enzymes.  Proteobacteria were found to dominate the mesophilic community while Actinobacteria were most abundant in the thermophilic community.  Analysis of protein family representation in each metagenome indicated that cellobiohydrolases containing carbohydrate binding module 2 (CBM2) were significantly overrepresented in the thermophilic community.  Micromonospora, a member of Actinobacteria, primarily housed these genes in the thermophilic community.  In light of these findings, Micromonospora and other closely related Actinobacteria genera appear to be promising sources of thermophilic lignocellulolytic enzymes for rice straw deconstruction under high-solids conditions.   Furthermore, these discoveries warrant future research to determine if exoglucanases with CBM2 represent thermostable enzymes tolerant to the extreme conditions of industrial biofuel production.