Functional roles of degraders and non-degraders in anaerobic trophic networks converting lignocellulose into monocarboxylates

Abstract

Lignocellulose is a promising renewable resource for anaerobic biochemical production, but its microbial conversion remains challenging. To elucidate metabolic networks in lignocellulose-degrading consortia, inocula of various origins were enriched on cellulose or xylan. Community composition and metabolic functions were revealed by amplicon sequencing, metagenomics, genome-scale metabolic modelling, and metabolic simulations. In cellulose-enriched communities, Fibrobacter and Lacrimispora consistently dominated as primary cellulose degraders, whereas Bacteroides likely functioned as secondary degraders. Acetic acid (up to 1.3 g l-1) and CO2 were the main fermentation products. Xylan enrichments produced C2-C6 fatty acids (up to 3.9 g l-1), lactic acid (up to 1.2 g l-1), ethanol (up to 1.2 g l-1), CO2, and H2. Clostridium dominated one xylan community and produced mainly butyric acid, while Bifidobacterium dominated another and produced mainly lactic acid. Caproic acid production was experimentally observed in one xylan enrichment. Metagenomic annotations and metabolic simulations suggest that Lacrimispora amygdalina degraded xylan and Robinsoniella peoriensis consumed xylobiose as a secondary consumer, both likely producing ethanol and lactic acid that supported caproic and butyric acid production by Caproicibacter fermentans. Integrated analysis identified functional guilds and clarified the roles of degraders and non-degraders, providing a blueprint for engineering synthetic consortia for sustainable biochemical production.