Characterization of plant biomass-degrading microbial consortia by metasecretomics-based approaches

In this study, we performed a characterization of the proteins secreted (metasecretome) by four soil-derived microbial consortia bred on wheat straw (RWS and WS1-M), switchgrass (SG-M) and corn stover (CS-M) under mesophilic and aerobic conditions. Liquid chromatography-tandem mass spectrometry was used to analyze the metasecretome of RWS when was grown on wheat straw, xylose or xylan as a only carbon sources. Moreover, we analyzed the metasecretomes of WS1-M, SG-M and CS-M using nine chromogenic polysaccharide hydrogels and three insoluble chromogenic biomass substrates. In RWS, totals of 768 proteins were taxonomically and functionally classified. These proteins were mostly affiliated with Sphingobacterium-like consortium members (~50%). Specific abundant protein clusters were predicted to be involved in polysaccharide transport and/or sensing (TonB depend receptors). In addition, proteins predicted to degrade plant biomass, i.e. endo-1,4-beta-xylanases (GH10), beta-xylosidases/alpha-L-arabinofuranosidases (GH43 and GH51), pullulanases (GH13) and alpha-L-fucosidases (GH 95), were prominent. Otherwise, the metasecretomics-based analyses of WS1-M, SG-M and CS-M showed the presence of enzymes able to deconstruct arabinan, arabinoxylan, xylan, beta-glucan, galactomannan and rhamnogalacturonan. Interestingly, these last consortial metasecretomes contain enzyme cocktails that enable us to produce oligosaccharides directly from wheat straw, sugarcane bagasse and willow. Based on these results, we catalogue our four microbial consortia as true microbial enzyme factories, constituting excellent sources for the production of efficient enzyme cocktails for the pretreatment and saccharification of lignocellulose in diverse raw materials.