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Abstract:
Nitric oxide (NO) has important functions in biology and atmospheric
chemistry as a toxin, signaling molecule, ozone depleting agent and the
precursor of the greenhouse gas nitrous oxide (N2O). Although NO is a
potent oxidant, and was available on Earth earlier than oxygen, it is
unclear whether NO can be used by microorganisms for growth. Anaerobic
ammonium-oxidizing (anammox) bacteria couple nitrite reduction to
ammonium oxidation with NO and hydrazine as intermediates, and produce
N-2 and nitrate. Here, we show that the anammox bacterium Kuenenia
stuttgartiensis is able to grow in the absence of nitrite by coupling
ammonium oxidation to NO reduction, and produce only N-2. Under these
growth conditions, the transcription of proteins necessary for NO
generation is downregulated. Our work has potential implications in the
control of N2O and NO emissions from natural and manmade ecosystems,
where anammox bacteria contribute significantly to N-2 release to the
atmosphere. We hypothesize that microbial NO-dependent ammonium
oxidation may have existed on early Earth.
