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Abstract:
The release of abiotic methane from marine seeps into the atmosphere is
a major source of this potent greenhouse gas. Methanotrophic
microorganisms in methane seeps use methane as carbon and energy source,
thus significantly mitigating global methane emissions. Here, we
investigated microbial methane oxidation at the sediment-water interface
of a shallow marine methane seep. Metagenomics and metaproteomics,
combined with C-13-methane stable isotope probing, demonstrated that
various members of the gammaproteobacterial family Methylococcaceae were
the key players for methane oxidation, catalysing the first reaction
step to methanol. We observed a transfer of carbon to methanol-oxidizing
methylotrophs of the betaproteobacterial family Methylophilaceae,
suggesting an interaction between methanotrophic and methylotrophic
microorganisms that allowed for rapid methane oxidation. From our
microcosms, we estimated methane oxidation rates of up to 871 nmol of
methane per gram sediment per day. This implies that more than 50% of
methane at the seep is removed by microbial oxidation at the
sediment-water interface, based on previously reported in situ methane
fluxes. The organic carbon produced was further assimilated by different
heterotrophic microbes, demonstrating that the methane-oxidizing
community supported a complex trophic network. Our results provide
valuable eco-physiological insights into this specialized microbial
community performing an ecosystem function of global relevance.
