Microbial Community Structures in Family Anaerobic Digesters Reveal Potentially Differing Waste Conversion Pathways

Family-scale rural digesters are widely implemented in Nepal for waste management, resource recovery, and environmental stewardship for distributed communities. However, there is little documentation on the microbial community structures in real-world family farm digesters. This work compared microbial community structures in four family digesters with a near-by municipal digester. Included in the family digesters was a high-altitude family digester located on Mt. Everest in Mosi, Nepal (2,634 m elevation). Differences in the community structures included the prevalence in family digesters of Bathyarchaeota MGC-6. MCG-6 is an archaeal population putatively involved in autotrophic acetate generation and conversion of cellulose to sugars. In addition, Rikenellaceae DMER64, a population thought to degrade sugars, was more prevalent in the family digesters. The ratio of Methanothrix to hydrogenotrophic methanogens was higher in the family digesters. In addition, the dominant species of syntrophic hydrogen-producing bacteria differed. Syntrophobacter and Syntrophomonas species, documented for their critical roles in waste activated sludge digesters, were not detected. In conclusion, observed differences in microbial community composition suggested a capacity to support different substrate conversion pathways and a major role of Archaea beyond methanogenesis among the studied digesters.