Kinetic and metagenomic exploration of uncoupling hydrolysis and methanogenesis in an enriched cellulose-degrading anaerobic digestion community

Cellulose degradation is the main limitation in biogas production from anaerobic digestion of lignocellulosic biomass. To improve this, a microbial consortium was developed by enriching an inoculum from a goat manure-fed biogas plant in consecutive 14-day batch cycles. Using a carbon-balance approach, the 37th enrichment cycle achieved over 90% of the estimated potential cellulose conversion within 6 days, a significant increase from 59% in the initial cycle. A gene-centric metagenomic analysis revealed that the microbial community shifted towards specialization, with endocellulase genes and carbohydrate-binding modules increasing 1.6-and 1.7-fold from the initial cycle, respectively. Reconstruction of 85 Metagenome-Assembled Genomes detailed the complete metabolic pathway from cellulose to methane. This analysis identified a core cellulolytic group reliant on secreted enzymes across dominant phyla like Fibrobacterota, Chloroflexota, Planctomycetota, and Spirochaetota. These effective cellulose degraders, such as Fibrobacter and the families Paludibacteraceae and Anaerobacaceae, accounted for 17.8% relative abundance. Although the enrichment process created a metabolic bottleneck where rapid volatile fatty acids production inhibited methanogenesis, this consortium holds high potential for bioaugmentation. Ultimately, this study highlights the highly efficient microbial community capable of rapid cellulose degradation, providing the essential genomic profile to optimize future lignocellulosic anaerobic digestion systems.