Assessing contribution of anaerobic methane oxidation and its active methanotrophic communities in landfills

Methane (CH₄) mitigation in landfills is significantly influenced by anaerobic oxidation of methane (AOM), yet the specific microbial communities responsible and their role remain poorly characterized. Herein, AOM and its associated microorganisms were characterized in an aerated bioremediation landfill and two anaerobic landfills using DNA-stable isotope probing technique as well as pmoA sequencing. The AOM activity of the landfilled wastes was 5.02-20.43 nmol g^-1 h^-1 with a higher activity observed in the aerated landfill compared to the anaerobic ones. The potential CH₄ consumption by AOM was estimated to be up to about 2.99 kg t^-1 in Chinese landfills, accounting for about 2.91% of the total CH₄ produced. The pmoA-methanotrophs were abundant in the landfills with 1.84 × 10⁶-5.37 × 10⁷ copies g^-1.The major active methanotrophs involved in AOM in the landfills included type I methanotrophs Methylocaldum, Methylobacter, Methylomicrobium, Methylovulum and Methylomonas, and type II methanotrophs Methylocystis and Methylosinus. Among them, type II methanotrophs dominated in the aerated landfill, while type I methanotrophs were predominant in the anaerobic landfills. NO₃^--N and Fe³⁺ emerged as key environmental factors influencing the active pmoA-methanotrophic community, likely attributed to their role as electron acceptors under anoxic conditions. The prominent presence of Methanobacterium and Methanosarcina in the ¹³C-DNA, combined with the strong correlation between total Fe and the mcrA community, implied that AOM coupled to Fe³⁺ reduction via reverse methanogenesis occurred. These findings are helpful for evaluating AOM-driven CH₄ consumption and understanding the functional microorganisms mediating this process in landfill ecosystems.