Research progress and prospects of metal-dependent anaerobic methane oxidation in marine sediments

A large fraction of methane is consumed by anaerobic oxidation (AOM) in marine sediments. Previous researches suggested that AOM is coupled to the reduction of sulfate, nitrate and nitrite, which may effectively reduce methane emission into the atmosphere. Recently, metal-dependent AOM (metal-AOM, AOM driven by active metal oxides reduction reaction) was demonstrated to occur in both the sediments in nature and enriched cultures. But the elusive microorganisms mediating metal-AOM process have not yet been isolated from natural marine environments, and most researches on metal-AOM in marine sediments focus on special marine habitats such as hydrothermal vents or cold seeps. However, a series of investigation shows that geological fluids play an important role in the maintenance and evolution of these submarine chemolithoautotrophy ecosystems, and profoundly affect the global geochemical cycle. Therefore, the research on this scientific problem has attracted more and more attention from marine scientists. In this review, the potential microbial communities and geochemical evidence of metal-AOM in marine sediments are summarized. On the basis of literature researches, taking the cold seeps and hydrothermal vents coexisted region, the Okinawa Trough, as an example, a new metal-AOM mechanism is proposed. The investigation in the global cold seeps and hydrothermal vents system interaction areas could be beneficial to better discuss the mechanism of metal-AOM and the connectivity of microbial distribution in deep-sea habitats.