Nitrospira moscoviensis strain:NSP M-1 Genome sequencing. Nitrospira moscoviensis strain:NSP M-1

Nitrospira are a diverse group of nitrite-oxidizing bacteria and among the environmentally most widespread nitrifiers. Despite this, they remain scarcely studied and mostly uncultured. Based on genomic and experimental data from Nitrospira moscoviensis representing the ubiquitous Nitrospira lineage II, we identified ecophysiological traits that contribute to the ecological success of Nitrospira. Unexpectedly, N. moscoviensis possesses genes coding for a urease and cleaves urea to ammonia and CO2. Ureolysis was not observed yet in nitrite oxidizers and enables N. moscoviensis to supply ammonia oxidizers lacking urease with ammonia from urea, which is fully nitrified by this consortium through reciprocal feeding. The presence of highly similar urease genes in Nitrospira lenta from activated sludge, in metagenomes from soils and freshwater habitats, and of other ureases in marine nitrite oxidizers, suggests a wide distribution of this extended interaction between nitrifiers, which enables nitrite oxidizers to tap urea as a source of energy. A soluble formate dehydrogenase lends additional ecophysiological flexibility and allows N. moscoviensis to utilize formate aerobically, with or without concomitant nitrite oxidation, or anaerobically with nitrate as terminal electron acceptor. Compared to Nitrospira defluvii from lineage I, N. moscoviensis shares the Nitrospira core metabolism but shows substantial genomic dissimilarity including genes for adaptations to elevated oxygen concentrations. Reciprocal feeding and metabolic versatility, including the participation in different nitrogen cycling processes, likely are key factors for the niche partitioning, the ubiquity, and the high diversity of Nitrospira in natural and engineered ecosystems.