AUTHOR=Hou Ting-Ting , Miao Li-Li , Peng Ji-Sen , Ma Lan , Huang Qiang , Liu Ying , Wu Meng-Ru , Ai Guo-Min , Liu Shuang-Jiang , Liu Zhi-Pei 

TITLE=Dirammox Is Widely Distributed and Dependently Evolved in Alcaligenes and Is Important to Nitrogen Cycle

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.864053

DOI=10.3389/fmicb.2022.864053

ISSN=1664-302X

ABSTRACT=<p>Nitrogen cycle is an essential process for environmental health. Dirammox (<italic>dir</italic>ect <italic>amm</italic>onia <italic>ox</italic>idation), encoded by the <italic>dnfT1RT2ABCD</italic> cluster, was a novel pathway for microbial N<sub>2</sub> production defined in <italic>Alcaligenes ammonioxydans</italic> HO-1. Here, a copy of the cluster <italic>dnfT1RT2ABCD</italic> as a whole was proved to have existed and very conserved in all <italic>Alcaligenes</italic> genomes. Phylogenetic analyses based on 16S rRNA gene sequences and amino acid sequences of DnfAs, together with G + C content data, revealed that <italic>dnf</italic> cluster was evolved associated with the members of the genus <italic>Alcaligenes</italic>. Under 20% O<sub>2</sub> conditions, 14 of 16 <italic>Alcaligenes</italic> strains showed Dirammox activity, which seemed likely taxon-related. However, the <italic>in vitro</italic> activities of DnfAs catalyzing the direct oxidation of hydroxylamine to N<sub>2</sub> were not taxon-related but depended on the contents of Fe and Mn ions. The results indicated that DnfA is necessary but not sufficient for Dirammox activity. The fact that members of the genus <italic>Alcaligenes</italic> are widely distributed in various environments, including soil, water bodies (both freshwater and seawater), sediments, activated sludge, and animal–plant-associated environments, strongly suggests that Dirammox is important to the nitrogen cycle. In addition, <italic>Alcaligenes</italic> species are also commonly found in wastewater treatment plants, suggesting that they might be valuable resources for wastewater treatment.</p>