Anaerobic methane oxidation coupled to denitrification is the dominant methane sink in a deep lake

Evidence whether the recently discovered denitrification-dependent methane oxidation (nitrate/nitrite-dependent anaerobic methane oxidation, n-damo) represents a major methane sink or an insignificant side aspect in the global methane cycle is scarce. High-resolution microprofiles measured in intact sediment cores close to in situ conditions, anoxic incubations of intact sediments, and quantification of the responsible microorganisms with molecular techniques proved n-damo to be the major methane sink in Lake Constance, one of the best-studied freshwater lakes. The n-damo process has long been overlooked because of the close proximity of aerobic and anaerobic activities. Our study documents that a large part of methane previously thought to be oxidized aerobically is in fact oxidized anaerobically by physiologically entirely different organisms.