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

Joerg S. Deutzmann, Peter Stief, Josephin Brandes, Bernhard Schink

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Anaerobic methane oxidation coupled to denitrification, also
known as “nitrate/nitrite-dependent anaerobic methane oxidation”
(n-damo), was discovered in 2006. Since then, only a few studies
have identified this process and the associated microorganisms in
natural environments. In aquatic sediments, the close proximity of
oxygen- and nitrate-consumption zones can mask n-damo as aerobic
methane oxidation. We therefore investigated the vertical distribution
and the abundance of denitrifying methanotrophs related
to Candidatus Methylomirabilis oxyfera with cultivation-independent
molecular techniques in the sediments of Lake Constance. Additionally,
the vertical distribution of methane oxidation and nitrate
consumption zones was inferred from high-resolution microsensor
profiles in undisturbed sediment cores. M. oxyfera-like bacteria
were virtually absent at shallow-water sites (littoral sediment) and
were very abundant at deep-water sites (profundal sediment). In
profundal sediment, the vertical distribution of M. oxyfera-like bacteria
showed a distinct peak in anoxic layers that coincided with the
zone of methane oxidation and nitrate consumption, a strong indication
for n-damo carried out by M. oxyfera-like bacteria. Both
potential n-damo rates calculated from cell densities (660–4,890
μmol CH4·m−2·d−1) and actual rates calculated from microsensor
profiles (31–437 μmol CH4·m−2·d−1) were sufficiently high to prevent
methane release from profundal sediment solely by this
process. Additionally, when nitrate was added to sediment cores
exposed to anoxic conditions, the n-damo zone reestablished well
below the sediment surface, completely preventing methane release
from the sediment. We conclude that the previously overlooked
n-damo process can be the major methane sink in stable
freshwater environments if nitrate is available in anoxic zones.
TidsskriftProceedings of the National Academy of Science of the United States of America
Udgave nummer51
Sider (fra-til)18273–18278
StatusUdgivet - 23. dec. 2014


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