Geochemical transition zone powering microbial growth in subsurface sediments

Rui Zhao, José M Mogollón, Sophie S Abby, Christa Schleper, Jennifer F Biddle, Desiree L Roerdink, Ingunn H Thorseth, Steffen L Jørgensen

No other environment hosts as many microbial cells as the marine sedimentary biosphere. While the majority of these cells are expected to be alive, they are speculated to be persisting in a state of maintenance without net growth due to extreme starvation. Here, we report evidence for in situ growth of anaerobic ammonium-oxidizing (anammox) bacteria in ∼80,000-y-old subsurface sediments from the Arctic Mid-Ocean Ridge. The growth is confined to the nitrate-ammonium transition zone (NATZ), a widespread geochemical transition zone where most of the upward ammonium flux from deep anoxic sediments is being consumed. In this zone the anammox bacteria abundances, assessed by quantification of marker genes, consistently displayed a four order of magnitude increase relative to adjacent layers in four cores. This subsurface cell increase coincides with a markedly higher power supply driven mainly by intensified anammox reaction rates, thereby providing a quantitative link between microbial proliferation and energy availability. The reconstructed draft genome of the dominant anammox bacterium showed an index of replication (iRep) of 1.32, suggesting that 32% of this population was actively replicating. The genome belongs to a Scalindua species which we name Candidatus Scalindua sediminis, so far exclusively found in marine sediments. It has the capacity to utilize urea and cyanate and a mixotrophic lifestyle. Our results demonstrate that specific microbial groups are not only able to survive unfavorable conditions over geological timescales, but can proliferate in situ when encountering ideal conditions with significant consequences for biogeochemical nitrogen cycling.

Department für Funktionelle und Evolutionäre Ökologie
Externe Organisation(en)
University of Bergen (UiB), University of Delaware, Leiden University
Proceedings of the National Academy of Sciences of the United States of America (PNAS)
ÖFOS 2012
106022 Mikrobiologie
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