In order to further optimize anaerobic digestion and increase methane yield, there is a strong need to better understand the microbiome that is driving the biological process. Cellulosic biomass is an abundant resource that can serve as a sustainable feedstock for methane generation. However, because cellulose and xylan are recalcitrant, effective hydrolysis is an essential prerequisite for a process to be effective. This study examined five methanogenic enrichment cultures that robustly digested cellulose or xylan anaerobically for over two years under mesophilic or thermophilic conditions. Metagenomics and metatranscriptomics were applied to reconstruct the meta-metabolic network and unravel the ecological roles of microbial populations in the enrichments. Differential coverage binning was used to reconstruct population genomes. A total of 107 population genomes were reconstructed from the five enrichments. During a timecourse experiment, only a subset of the population genomes was transcriptionally active. The inocula used to derive the enrichments were obtained from two different wastewater anaerobic digesters. However, after long-term enrichment, phylogenetic convergence of the active populations by enrichment condition and phase of fermentation was observed. In the mesophilic cellulose enrichment cultures, Clostridium cellulolyticum-related and Ruminococcus-related bacteria were found to function as hydrolyzers and primary fermenters during the early phase of the process, while Clostridium leptum-related bacteria were active towards the later phase as secondary fermenters and fatty acid scavengers. Hydrogenotrophic methanogens were active as the last step of the trophic chain. A similar meta-metabolism and trophic roles were found in the other enrichment cultures, but the active functional populations were distinct between enrichment conditions. Overall, by reconstructing the meta-metabolism, a comprehensive understanding of the anaerobic digestion microbiome that converted cellulosic biomass to methane was obtained and such information can assist microbiologists and engineers to manipulate the microbiome and operating conditions to increase methane yield and process efficiency.

Reconstruction of cellulose-to-methane trophic chain from metagenomics and metatranscriptomics

255th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.