Microbial methane oxidation has a significant impact
on the methane
flux from marine gas hydrate areas. However, the environmental fate
of methane remains poorly constrained. We quantified the relative
contributions of aerobic and anaerobic methanotrophs to methane consumption
in sediments of the gas hydrate-bearing Sakata Knoll, Japan, by in situ geochemical and microbiological analyses coupled
with 13C-tracer incubation experiments. The anaerobic ANME-1
and ANME-2 species contributed to the oxidation of 33.2 and 1.4% methane
fluxes at 0–10 and 10–22 cm below the seafloor (bsf),
respectively. Although the aerobic Methylococcaceae species consumed
only 0.9% methane flux in the oxygen depleted 0.0–0.5 cmbsf
zone, their metabolic activity was sustained down to 6 cmbsf (based
on rRNA and lipid biosyntheses), increasing their contribution to
10.3%. Our study emphasizes that the co-occurrence of aerobic and
anaerobic methanotrophy at the redox transition zone is an important
determinant of methane flux.