State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, No. 1 Beichen West Road, Chaoyang District, Beijing 100101, P. R. China.
School of Life Sciences, University of Chinese Academy of Sciences, No. 1 Yanqihu East Road, Huairou District, Beijing 100049, P. R. China.
ISME J. 2024 Jan 8;18(1). doi: 10.1093/ismejo/wrae174.
Heterotrophic nitrification remains a mystery for decades. It has been commonly hypothesized that heterotrophic nitrifiers oxidize ammonia to hydroxylamine and then to nitrite in a way similar to autotrophic AOA and AOB. Recently, heterotrophic nitrifiers from Alcaligenes were found to oxidize ammonia to hydroxylamine and then to N2 ("dirammox", direct ammonia oxidation) by the gene cluster dnfABC with a yet-to-be-reported mechanism. The role of a potential glutamine amidotransferase DnfC clues the heterotrophic ammonia oxidation might involving in glutamine. Here, we found Alcaligenes faecalis JQ135 could oxidize amino acids besides ammonia. We discovered that glutamine is an intermediate of the dirammox pathway and the glutamine synthetase gene glnA is essential for both A. faecalis JQ135 and the Escherichia coli cells harboring dnfABC gene cluster to oxidize amino acids and ammonia. Our study expands understanding of heterotrophic nitrifiers and challenges the classical paradigm of heterotrophic nitrification.
异养硝化作用几十年来一直是个谜。人们普遍假设，异养硝化菌以类似于自养 AOA 和 AOB 的方式将氨氧化为羟胺，然后再氧化为亚硝酸盐。最近，从产碱杆菌中发现的异养硝化菌通过尚未报道的机制，利用基因簇 dnfABC 将氨氧化为羟胺，然后氧化为 N2（“dirammox”，直接氨氧化）。尚未报道的一种潜在的谷氨酰胺酰胺转移酶 DnfC 的作用表明，异养氨氧化可能涉及谷氨酰胺。在这里，我们发现了 JQ135 可以氧化除氨以外的氨基酸。我们发现谷氨酰胺是 dirammox 途径的中间产物，谷氨酰胺合成酶基因 glnA 对于 JQ135 和含有 dnfABC 基因簇的大肠杆菌细胞氧化氨基酸和氨都是必需的。我们的研究扩展了对异养硝化菌的理解，并挑战了异养硝化的经典模式。
