Chemolithoautotrophic nitrite-oxidising bacteria (NOB) of the genus Nitrospira contribute to nitrification in diverse natural environments and engineered systems. Nitrospira are thought to be well-adapted to substrate limitation owing to their high affinity for nitrite and capacity to use alternative energy sources. Here, we demonstrate that the canonical nitrite oxidiser Nitrospira moscoviensis oxidises hydrogen (H₂) below atmospheric levels using a high-affinity group 2a nickel-iron hydrogenase [K_m(app) = 32 nM]. Atmospheric H₂ oxidation occurred under both nitrite-replete and nitrite-deplete conditions, suggesting low-potential electrons derived from H₂ oxidation promote nitrite-dependent growth and enable survival during nitrite limitation. Proteomic analyses confirmed the hydrogenase was abundant under both conditions and indicated extensive metabolic changes occur to reduce energy expenditure and growth under nitrite-deplete conditions. Thermodynamic modelling revealed that H₂ oxidation theoretically generates higher power yield than nitrite oxidation at low substrate concentrations and significantly contributes to growth at elevated nitrite concentrations. Collectively, this study suggests atmospheric H₂ oxidation enhances the growth and survival of NOB amid variability of nitrite supply, extends the phenomenon of atmospheric H₂ oxidation to an eighth phylum (Nitrospirota), and reveals unexpected new links between the global hydrogen and nitrogen cycles. Long classified as obligate nitrite oxidisers, our findings suggest H₂ may primarily support growth and survival of certain NOB in natural environments.

Nitrospira属的化能自养亚硝酸盐氧化细菌 (NOB)有助于多种自然环境和工程系统中的硝化作用。Nitrospira被认为能够很好地适应底物限制，因为它们对亚硝酸盐具有高亲和力并且能够使用替代能源。在这里，我们证明了典型的亚硝酸盐氧化剂Nitrospira moscoviensis使用高亲和力 2a 组镍铁氢化酶 [ K _m(app) = 32 nM]氧化低于大气水平的氢气 (H _{2 )。}大气中的H ₂氧化在亚硝酸盐充足和亚硝酸盐耗尽的条件下发生，这表明来自H ₂氧化的低电势电子促进亚硝酸盐依赖性生长并在亚硝酸盐限制期间能够存活。蛋白质组学分析证实，在两种条件下氢化酶都丰富，并表明在亚硝酸盐耗尽的条件下发生了广泛的代谢变化，以减少能量消耗和生长。热力学模型表明，理论上，在低底物浓度下，H ₂氧化比亚硝酸盐氧化产生更高的功率产率，并且在升高的亚硝酸盐浓度下显着促进生长。总的来说，这项研究表明，在亚硝酸盐供应变化的情况下，大气 H ₂氧化增强了 NOB 的生长和生存，将大气 H ₂氧化现象扩展到第八门（Nitrospirota），并揭示了全球氢和氮循环之间意想不到的新联系。长期以来被归类为专性亚硝酸盐氧化剂，我们的研究结果表明 H ₂可能主要支持某些 NOB 在自然环境中的生长和生存。