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Oxidizing hydrogen in place of nitrite
Microorganisms are important drivers of Earth's nitrogen cycle. Many of the organisms responsible for mediating the reactions of one phase of nitrogen to another are thought to be ecologic specialists. Using a combination of genomic and experimental analyses, Koch et al. show that Nitrospira moscoviensis, a member of a widely distributed genus of nitrite-oxidizing bacteria, can oxidize hydrogen instead of nitrite to support growth when oxygen is present. Not only does this ecologic flexibility suggest a broader distribution of these organisms in natural settings, but they may be important in engineered environments as well.
Science, this issue p. 1052
The bacterial oxidation of nitrite to nitrate is a key process of the biogeochemical nitrogen cycle. Nitrite-oxidizing bacteria are considered a highly specialized functional group, which depends on the supply of nitrite from other microorganisms and whose distribution strictly correlates with nitrification in the environment and in wastewater treatment plants. On the basis of genomics, physiological experiments, and single-cell analyses, we show that Nitrospira moscoviensis, which represents a widely distributed lineage of nitrite-oxidizing bacteria, has the genetic inventory to utilize hydrogen (H2) as an alternative energy source for aerobic respiration and grows on H2 without nitrite. CO2 fixation occurred with H2 as the sole electron donor. Our results demonstrate a chemolithoautotrophic lifestyle of nitrite-oxidizing bacteria outside the nitrogen cycle, suggesting greater ecological flexibility than previously assumed.