Chemolithoautotrophic nitrite-oxidizing bacteria (NOB) are key players in global nitrogen and carbon cycling. Members of the phylum Nitrospinae are the most abundant, known NOB in the oceans. To date, only two closely affiliated Nitrospinae species have been isolated, which are only distantly related to the environmentally abundant uncultured Nitrospinae clades. Here, we applied live cell sorting, activity screening, and subcultivation on marine nitrite-oxidizing enrichments to obtain novel marine Nitrospinae. Two binary cultures were obtained, each containing one Nitrospinae strain and one alphaproteobacterial heterotroph. The Nitrospinae strains represent two new genera, and one strain is more closely related to environmentally abundant Nitrospinae than previously cultured NOB. With an apparent half-saturation constant of 8.7 ± 2.5 µM, this strain has the highest affinity for nitrite among characterized marine NOB, while the other strain (16.2 ± 1.6 µM) and Nitrospina gracilis (20.1 ± 2.1 µM) displayed slightly lower nitrite affinities. The new strains and N. gracilis share core metabolic pathways for nitrite oxidation and CO₂ fixation but differ remarkably in their genomic repertoires of terminal oxidases, use of organic N sources, alternative energy metabolisms, osmotic stress and phage defense. The new strains, tentatively named “Candidatus Nitrohelix vancouverensis” and “Candidatus Nitronauta litoralis”, shed light on the niche differentiation and potential ecological roles of Nitrospinae.

化能自养亚硝酸盐氧化细菌（NOB）是全球氮和碳循环的关键参与者。 Nitrospinae 门的成员是海洋中已知数量最多的 NOB。迄今为止，仅分离出两种密切相关的硝化螺亚科物种，它们与环境丰富的未培养的硝化螺亚科分支只有远缘关系。在这里，我们对海洋亚硝酸盐氧化富集应用活细胞分选、活性筛选和传代培养，以获得新型海洋硝化脊椎亚科。获得了两个二元培养物，每个培养物含有一种 Nitrospinae 菌株和一种α变形菌异养菌。 Nitrospinae 菌株代表了两个新属，其中一个菌株比以前培养的 NOB 与环境丰富的 Nitrospinae 关系更密切。该菌株的表观半饱和常数为 8.7 ± 2.5 µM，在特征性海洋 NOB 中对亚硝酸盐具有最高的亲和力，而其他菌株 (16.2 ± 1.6 µM) 和Nitrospina gracilis (20.1 ± 2.1 µM) 的亚硝酸盐亲和力略低。新菌株和N. gracilis共享亚硝酸盐氧化和 CO ₂固定的核心代谢途径，但在末端氧化酶的基因组库、有机氮源的使用、替代能量代谢、渗透应激和噬菌体防御方面存在显着差异。这些新菌株暂定名为“ Candidatus Nitrohelix vancouverensis”和“ Candidatus Nitronauta litoralis”，揭示了 Nitrospinae 的生态位分化和潜在生态作用。