Incomplete denitrification phenotypes in diverse Thermus species from diverse geothermal spring sediments and adjacent soils in southwest China

Abstract

A few members of the bacterial genus Thermus have been shown to be incomplete denitrifiers, terminating with nitrite (NO2−) or nitrous oxide (N2O). However, the denitrification abilities of the genus as a whole remain poorly characterized. Here, we describe diverse denitrification phenotypes and genotypes of a collection of 24 strains representing ten species, all isolated from a variety of geothermal systems in China. Confirmed terminal products of nitrate reduction were nitrite or N2O, while nitric oxide (NO) was inferred as the terminal product in some strains. Most strains produced N2O; complete denitrification was not observed. Denitrification phenotypes were largely consistent with the presence of denitrification genes, and strains of the same species often had the same denitrification phenotypes and largely syntenous denitrification gene clusters. Genes for nirS and nirK coexisted in three Thermus brockianus and three Thermus oshimai genomes, which is a unique hallmark of some denitrifying Thermus strains and may be ecologically important. These results show that incomplete denitrification phenotypes are prominent, but variable, within and between Thermus species. The incomplete denitrification phenotypes described here suggest Thermus species may play important roles in consortial denitrification in high-temperature terrestrial biotopes where sufficient supply of oxidized inorganic nitrogen exists.

Phylogenomic analyses and comparative genomic studies of Thermus strains isolated from Tengchong and Tibet hot springs, China

“…Similarly, isolates YIM 77359, YIM 1640, YIM QC-2-109, YIM 77923, YIM 77838, and YIM 1627 having norB genes while other genomes of Thermus lacking these genes (FigureS8). The present study is consistent with earlier studies that nitrous oxide reductase (nosZ) genes are absent in Thermus species(Hedlund et al 2011;Mefferd et al 2022;Jiao et al 2022;Li et al 2022). So, the present genome data highlight the variability of incomplete denitri cation pathways among the Thermus strains (Figure…”

“…Strain T. parvatiensis RL also containing genes for arsenic resistance (Tripathi et al 2017). Thermus members have incomplete set of genes for denitri cation pathways (Hedlund et al 2011;Mefferd et al 2022), and genes encoded for enzymes in denitri cation pathway (narG, nirS, and norB) have acquired by the last common ancestor of Thermales and were inherited vertically expect nirK (Jiao et al 2022). Thermus genomes have high plasticity (Brüggemann and Chen 2006) and natural competence to transform DNA (Lorenz and Wackernagel 1994).…”