AUTHOR=Wang Liping , Shao Zongze 

TITLE=Aerobic Denitrification and Heterotrophic Sulfur Oxidation in the Genus Halomonas Revealed by Six Novel Species Characterizations and Genome-Based Analysis

JOURNAL=Frontiers in Microbiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.652766

DOI=10.3389/fmicb.2021.652766

ISSN=1664-302X

ABSTRACT=<p>Bacteria of <italic>Halomonas</italic> are widely distributed in various environments and play a substantial role in the nutrient cycle. In this report, 14 strains capable of aerobic denitrification and heterotrophic sulfur oxidation were isolated from different habitats. Based on the phenotypic, genotypic, and chemotaxonomic analyses, these strains were considered to represent six novel species of the genus <italic>Halomonas</italic>, for which the names <italic>Halomonas zhangzhouensis</italic> sp. nov. type strain CXT3-11<sup>T</sup> ( = MCCC 1A11036<sup>T</sup> = KCTC 72087<sup>T</sup>), <italic>Halomonas aerodenitrificans</italic> sp. nov. CYD-9<sup>T</sup> ( = MCCC 1A11058<sup>T</sup> = KCTC 72088<sup>T</sup>), <italic>Halomonas sulfidoxydans</italic> sp. nov. CYN-1-2<sup>T</sup> ( = MCCC 1A11059<sup>T</sup> = KCTC 72089<sup>T</sup>), <italic>Halomonas ethanolica</italic> sp. nov. CYT3-1-1<sup>T</sup> ( = MCCC 1A11081<sup>T</sup> = KCTC 72090<sup>T</sup>), <italic>Halomonas sulfidivorans</italic> sp. nov. NLG_F1E<sup>T</sup> ( = MCCC 1A13718<sup>T</sup> = KCTC 72091<sup>T</sup>), and <italic>Halomonas tianxiuensis</italic> sp. nov. BC-M4-5<sup>T</sup> ( = MCCC 1A14433<sup>T</sup> = KCTC 72092<sup>T</sup>) are proposed. Intriguingly, they formed a unique group with 11 other species designated as the “<italic>H. desiderata</italic> group.” To better understand their featured metabolisms, genes involved in denitrification and sulfur oxidation were analyzed, along with 193 other available genomes of the whole genus. Consistently, complete denitrification pathways were confirmed in the “<italic>H. desiderata</italic> group,” in which <italic>napA</italic>, <italic>narG</italic>, <italic>nirS</italic>, <italic>norB</italic>, and <italic>nosZ</italic> genes coexist. Their nitrite reductase NirS formed a unique evolutionary lineage, distinguished from other denitrifiers in <italic>Halomonas</italic>. In addition, diverse occurrence patterns of denitrification genes were also observed in different phylogenetic clades of <italic>Halomonas</italic>. With respect to sulfur oxidation, <italic>fccAB</italic> genes involved in sulfide oxidation commonly exist in the “<italic>H. desiderata</italic> group,” while <italic>sqr</italic> genes are diverse and can be found in more species; <italic>sqr</italic> genes co-occurred with <italic>fccAB</italic> in eight strains of this study, contributing to more active sulfide oxidation. Besides, the <italic>tsdA</italic> gene, which encodes an enzyme that oxidizes thiosulfate to tetrathionate, is ubiquitous in the genus <italic>Halomonas</italic>. The widespread presence of <italic>sqr/fccAB</italic>, <italic>pdo</italic>, and <italic>tsdA</italic> in <italic>Halomonas</italic> suggests that many <italic>Halomonas</italic> spp. can act as heterotrophic sulfur oxidizers. These results provide comprehensive insights into the potential of denitrification and sulfur oxidation in the whole genus of <italic>Halomonas</italic>. With regard to the global distribution of <italic>Halomonas</italic>, this report implies their unneglectable role in the biogeochemical cycle.</p>