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