Physiological and genomic characterization of five cold-tolerant nitrite-oxidizing Nitrotoga strains

Chemolithoautotrophic production of nitrate is accomplished by the polyphyletic functional group of nitrite-oxidizing bacteria (NOB). A widely distributed and important NOB type in cold nitrogen removal systems is Nitrotoga, which however remains understudied due to the scarcity of cultivated representatives. Here, we present genomic features of five Nitrotoga strains from various habitats, including the first obligate marine species enriched from an aquaculture system. Comparative analysis of the Nitrotoga genomes showed, e.g., a unique gene repertoire of the marine strain that could be advantageous in its natural habitat and confirmed the lack of genes for assimilatory nitrite reduction in a strain found to require ammonium for growth. Overall, these data largely broaden our knowledge of Nitrotoga and elucidates the ecological role of this group of nitrite oxidizers.