Linking carbon, nitrogen and sulfur cycles: Electron transfer model for nitrate and sulfate dependent anaerobic...

Simultaneous nitrate and sulfate-dependent anaerobic oxidation of methane (AOM) regulated by anaerobic methanotrophic (ANME) archaea is a key process in the global carbon, nitrogen, and sulfur cycles. However methane oxidation activity and electron transfer mechanisms within the ANME consortia, including sulfate-reducing bacteria (SRB), NC10 and anaerobic ammonium oxidation bacteria, which are driven by different electron acceptors remain to be elucidated. An electron transfer model was developed to simulate direct interspecies electron transfer in sulfate-dependent AOM with a clade of ANME archaea and SRB cooperation at various ambient temperatures (5-30 ℃), as well as nitrate-dependent AOM and dissimilatory nitrate reduction to ammonia. In this model, the processes of methane oxidation and electron acceptor reduction were decoupled, with the introduction of intracellular electron carriers converting cyclically between oxidized and reduced forms, analogous to interspecies electron transfer by cell membrane cytochromes and pili-based nanowire networks. The developed model was calibrated and validated with long-term bioreactor continuous operation performance and batch experimental data. Results demonstrated that the model could effectively depict the ability of sulfate, nitrate, and nitrite to compete for electrons. The model successfully simulates direct electron transfer and competition mechanisms, providing a novel tool for understanding and optimizing linked carbon, nitrogen, and sulfur cycles.