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Abstract:
Bioavailable nitrogen is essential for all organisms and is the main limiting nutrient for life on our planet. This nitrogen enters the environment as ammonia produced by microbial or industrial fixation of nitrogen gas. It is lost, again as nitrogen gas, when microorganisms respire oxidized nitrogenous compounds, such as nitrate and nitrite, instead of oxygen. The process of nitrification — the oxidation of ammonia to nitrate by way of nitrite — links the gain and loss of bioavailable nitrogen and thus plays a central part in the nitrogen cycle. Since its discovery in 1890 (ref. 1), nitrification has been thought to be performed as a 'labour union', with distinct microorganisms carrying out the two steps. In this issue, Daims et al.2 (page 504) and van Kessel et al.3 (page 555) independently show that microorganisms from the genus Nitrospira can conduct complete nitrification on their own.
