Advances in the study of methane-metabolizing microbial communities in marine sediments

Methane is an important greenhouse gas affecting the global climate. Meanwhile, methane is a major component of natural gas hydrate which regarded as a potential energy resource below seafloor. Seafloor sediment is an important ecological region for methane biotransformation. The methanogens can use H₂, CO₂, and simple organic compounds (e.g. methanol, methylamines, dimethylsulfide) as substrates to produce methane. The methane produced in the bottom of the sediments would be consumed by aerobic methanotrophs and anaerobic methanotrophs during its upward migration, which reduces greatly the methane emissions to the atmosphere. Aerobic methane oxidation occurs mainly in oxygenated sediments and sediment-water interfaces, and is mediated by aerobic methane-oxidizing bacteria. However, most of the methane is consumed by anaerobic methane oxidation before it reaches the seafloor. The anaerobic methanotrophs oxidize methane coupled by SO₄²⁻, NO₂⁻/NO₃⁻ or Fe³⁺/Mn⁴⁺. We reviewed the status quo and perspectives of the taxonomy, metabolic and ecological diversity of methanogens and methanotrophs in marine sediments, and emphasized deficiencies and issues need to be solved in future studies. This review provided theoretical foundation for the study of biotransformation process and element coupling of methane in marine environment.