Uncovering anaerobic oxidation of methane and active microorganisms in landfills by using stable isotope probing

Anaerobic oxidation of methane (AOM) coupled electron acceptor reduction has been shown to regulate methane (CH₄) emissions from the habitats. Landfill is one of the most important anthropogenic CH₄ emission sources. However, the effect of electron acceptors on the AOM process and its microbial mechanism in landfills is poorly characterized. Herein, electron acceptors including nitrate, nitrite, sulfate and ferric iron were used to regulate the AOM process in landfill microcosms by using stable isotope probing analysis. The addition of electron acceptors could promote AOM in the landfilled waste. Among them, nitrate and nitrite had the strongest promoting effect on AOM in the waste with the maximum activities of 5.60-5.76 μg g^-1 d^-1, which increased by 1070.9%-1103.6% compared with the control without electron acceptor amendation. Candidatus Methylomirabilis was only detected in assimilating CH₄ in the ferric iron-amended treatment. The proteobacterial methanotrophs and Methylacidiphilum were mainly observed in the ferric iron ¹³C-DNA, likely due to O₂ released from the conversion of nitric oxide. Methanomassiliicoccus were the most abundant archaea in the treatments with nitrate, nitrite and sulfate, while Methanosarcina dominated in the ferric iron-amended treatment. Nitrate, nitrite, sulfate and ferric iron all could prompt the growth of sulfur, iron, nitrate and nitrite metabolizing microorganisms. Partial least squares path modeling indicated that AOM in the landfilled waste could be driven by electron acceptors via the changes of environmental variables, while the direct effect of electron acceptors on the AOM activity was weak with an intensity of 0.06. Taken together, this study demonstrated that the AOM process in landfills can be regulated by electron acceptors, especially nitrate and nitrite, to mitigate CH₄ emissions from landfills.