The recent discovery of bacteria within the genus Nitrospira capable of complete ammonia oxidation (comammox) demonstrated that the sequential oxidation of ammonia to nitrate via nitrite can also be performed within a single bacterial cell. Although comammox Nitrospira exhibit a wide distribution in natural and engineered ecosystems, information on their physiological properties is scarce due to the limited number of cultured representatives. Additionally, most available genomic information is derived from metagenomic sequencing and high-quality genomes of Nitrospira in general are limited. In this study, we obtained a high (90%) enrichment of a novel comammox species, tentatively named “Candidatus Nitrospira kreftii”, and performed a detailed genomic and physiological characterization. The complete genome of “Ca. N. kreftii” allowed reconstruction of its basic metabolic traits. Similar to Nitrospira inopinata, the enrichment culture exhibited a very high ammonia affinity (K_{m(app)_NH3} ≈ 0.040 ± 0.01 µM), but a higher nitrite affinity (K_{m(app)_NO2}- = 12.5 ± 4.0 µM), indicating an adaptation to highly oligotrophic environments. Furthermore, we observed partial inhibition of ammonia oxidation at ammonium concentrations as low as 25 µM. This inhibition of “Ca. N. kreftii” indicates that differences in ammonium tolerance rather than affinity could potentially be a niche determining factor for different comammox Nitrospira.

最近在Nitrospira 属中发现的能够完全氧化氨的细菌 (comammox) 表明，氨通过亚硝酸盐依次氧化为硝酸盐也可以在单个细菌细胞内进行。尽管 comammox Nitrospira在自然和工程生态系统中分布广泛，但由于培养代表的数量有限，有关其生理特性的信息很少。此外，大多数可用的基因组信息来自宏基因组测序，而Nitrospira的高质量基因组通常是有限的。在这项研究中，我们获得了一种新的 comammox 物种的高 (90%) 富集，暂定名为“ CandidatusNitrospira kreftii”，并进行了详细的基因组和生理学表征。“ Ca的完整基因组。N. kreftii”允许重建其基本代谢特征。与Nitrospira inopinata类似，富集培养物表现出非常高的氨亲和力（K _{m（app）_NH3}  ≈ 0.040 ± 0.01 µM），但具有更高的亚硝酸盐亲和力（K _{m（app）_NO2} - = 12.5 ± 4.0 µM），表明适应高度贫营养的环境。此外，我们观察到氨氧化在低至 25 µM 的铵浓度下部分抑制。这种抑制“ Ca. N. kreftii”表明铵耐受性而非亲和力的差异可能是不同 comammox Nitrospira的利基决定因素。