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Abstract:
A major role in regulation of global methanefluxes has been attributed to the process of anaerobic oxi-dation of methane (AOM), which is performed by consor-tia of methanotrophic archaea and sulfate reducing bacte-ria. An important question remains how these energy lim-ited, slow growing microorganisms with generation times of3–7 months respond to rapid natural variations in methanefluxes at cold seeps. We used an experimental flow-throughcolumn system filled with cold seep sediments naturallyenriched in methanotrophic communities, to test their re-sponses to short-term variations in methane and sulfatefluxes.At stable methane and sulfate concentrations of∼2 mM and 28 mM, respectively, we measured constant ratesof AOM and sulfate reduction (SR) for up to 160 days of in-cubation. When percolated with methane-free medium, theanaerobic methanotrophs ceased to produce sulfide. After astarvation phase of 40 days, the addition of methane restoredformer AOM and SR rates immediately. At methane con-centrations between 0–2.3 mM we measured a linear correla-tion between methane availability, AOM and SR. At constantfluid flow velocities of 30 m yr−1, ca. 50% of the methanewas consumed by the anaerobic methanotrophic (ANME)population at all concentrations tested. Reducing the sul-fate concentration from 28 to 1 mM, a decrease in AOMand SR by 50% was observed, and 45% of the methanewas consumed. Hence, the marine anaerobic methanotrophs(ANME) are capable of oxidizing substantial amounts ofmethane over a wide and variable range of fluxes of the reac-tion educts.
