Aerobic and anaerobic methanotrophs in the Black Sea water column

Abstract

Summary Inputs of CH 4 from sediments, including methane seeps on the continental margin and methane‐rich mud volcanoes on the abyssal plain, make the Black Sea the world’s largest surface water reservoir of dissolved methane and drive a high rate of aerobic and anaerobic oxidation of methane in the water column. Here we present the first combined organic geochemical and molecular ecology data on a water column profile of the western Black Sea. We show that aerobic methanotrophs type I are responsible for methane oxidation in the oxic water column and ANME‐1‐ and ANME‐2‐related organisms for anaerobic methane oxidation. The occurrence of methanotrophs type I cells in the anoxic zone suggests that inactive cells settle to deeper waters. Molecular and biomarker results suggest that a clear distinction between the occurrence of ANME‐1‐ and ANME‐2‐related lineages exists, i.e. ANME‐1‐related organisms are responsible for anaerobic methane oxidation below 600 m water depth, whereas ANME‐2‐related organisms are responsible for this process in the anoxic water column above approximately 600 m water depth.

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