Plant biomass-degrading microbial consortia: Ecology, lignocellulolytic machinery and biotechnological potential

The production of renewable bio-based compounds from plant biomass-derived sugars has increased exponentially in the last decade. In such processes, a key bottleneck is the often low saccharification efficiency, which is due to the recalcitrant nature of the plant lignocellulosic matter. The use of microbial consortia has been proposed as an attractive alternative for a more efficient degradation of these materials. Here, we report an in-depth characterization of different soil-derived microbial consortia that were cultivated on wheat straw, corn stover and switchgrass as sole sources of carbon and energy. Metataxonomic (16S rRNA / ITS1 amplicon-sequencing) and metagenomic (total DNA sequencing and screening of libraries) analyses were performed, yielding in-depth data on the microbial consortia that were bred. In these selected communities we observed the prevalence of particular members of the Enterobacteriales, Pseudomonadales, Flavobacteriales and Sphingobacteriales. Moreover, the collective secreted proteins were examined by liquid chromatography–tandem mass spectrometry and the enzymatic activities evaluated using a new generation of chromogenic substrates. Overall, the ecophysiology of the systems was characterized as being surprisingly complex and intricate. For example, the consortium structures remained complex and several consortium members had impact on the lignocellulose degradation process. The enzymatic potential of these consortia was found to encompass secreted xylanases, glucosidases, arabinofuranosidases, galactosidases, mannosidases and fucosidases. Moreover, an analysis of the metagenomic libraries unveiled several genes for novel thermo-alkaline-tolerant enzymes. The metagenomes and metasecretomes produced constitute valuable sources for the design of enzyme cocktails useful in the saccharification of lignocellulosic materials.