Dominance of acetoclastic methanogenesis in municipal solid waste (MSW) decomposition despite high variability in microbial community composition: insights form natural stable carbon isotope and metagenomic analyses

Understanding the dynamics of microbial community and metabolic pathways involved in methanogenesis during municipal solid waste (MSW) decomposition is crucial for effective methane (CH 4 ) management in landfills. This study investigated bacterial and methanogenic community composition, methanogenic metabolism, and their dynamics across typical phases of MSW decomposition-anaerobic acid phase, accelerated methanogenic phase, and decelerated methanogenic phase. Parallel bioreactors (A and B) were analyzed using metagenomics and natural stable carbon isotope analyses. CH 4 production kinetics for both reactors were accurately simulated by the Gompertz kinetic model (R 2 ​> ​0.98), Capturing key MSW decomposition phases characterized by variations in CH 4 production, pH, and volatile fatty acids (VFAs) concentrations. Concurrently, the methanogenic community transitioned from an initial dominance of acetoclastic methanogens Methanothrix in reactor A, and Methanothrix and Methanosarcina in reactor B to a co-dominance of hydrogenotrophic methanogens Methanobacterium and acetoclastic methanogens Methanothrix and Methanosarcina in both reactors. Acetate concentration and CH 4 yield were identified as primary factors shaping methanogen community structure. Acetoclastic methanogenesis remained the predominant pathway, accounting for 66.5–85.9 ​% of total methanogenesis modules., This dominance was supported by stable carbon isotope (α c constantly below 1.055 in both reactors) and metagenomic analyses, particularly the prevalence of acetate-metabolizing genes such as acetate kinase and acetyl-CoA synthetase . Despite substantial variability in microbial community composition, acetoclastic methanogenesis consistently dominated CH 4 production throughout MSW decomposition. These findings enhance understanding of methanogenesis in MSW landfills, supporting strategies to mitigate CH 4 emissions and address climate goals. • Acetate and methane yield shaped methanogen community structure. • Methanothrix and Methanosarcina competed for acetate. • Acetoclastic methanogenesis exhibited a strong correlation with acetate availability. • Acetoclastic methanogenesis predominated throughout the MSW decomposition.