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 is essential for both A. faecalis JQ135 and the E. 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.

中文翻译：

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粪产碱菌的异养硝化将有机和无机氮代谢联系起来


几十年来，异养硝化作用仍然是一个谜。人们普遍假设异养硝化菌将氨氧化成羟胺，然后氧化成亚硝酸盐，其方式类似于自养 AOA 和 AOB。最近，发现来自Alcaligenes的异养硝化细菌通过基因簇dnfABC将氨氧化成羟胺，然后氧化成N2（“dirammox”，直接氨氧化），其机制尚未报道。潜在的谷氨酰胺酰胺转移酶 DnfC 的作用提示了谷氨酰胺可能涉及的异养氨氧化。在这里，我们发现粪产碱菌JQ135可以氧化除氨之外的氨基酸。我们发现谷氨酰胺是 dirammox 途径的中间体，谷氨酰胺合成酶基因对于粪曲霉 JQ135 和含有 dnfABC 基因簇的大肠杆菌细胞氧化氨基酸和氨至关重要。我们的研究扩展了对异养硝化菌的理解，并挑战了异养硝化作用的经典范式。