![]() For example, Sanford and colleagues ( 2012) described so-called atypical nos genes, comprising all known nos genes outside the Pseudomonadota (formerly informally Proteobacteria (Oren and Garrity, 2021)), and showed that they are frequently present in genomes that do not contain other denitrification genes. However, microbes with truncated, incomplete, or alternative denitrification pathways are also known. Traditionally, most denitrifiers were thought to be full denitrifiers that catalyze all steps of the pathway (Zumft 1997). 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.Ĭomplete denitrification is the process by which microorganisms sequentially reduce nitrate (NO 3 −) to dinitrogen (N 2) through anaerobic respiration using the following enzyme complexes: nitrate reductase, Nar and/or Nap (NO 3 − → NO 2 −) nitrite reductase, NirS and/or NirK (NO 2 − → NO) nitric oxide reductase, Nor (NO → N 2O) and nitrous oxide reductase, Nos (N 2O → N 2). These results show that incomplete denitrification phenotypes are prominent, but variable, within and between Thermus species. 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. 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. Most strains produced N 2O complete denitrification was not observed. Confirmed terminal products of nitrate reduction were nitrite or N 2O, while nitric oxide (NO) was inferred as the terminal product in some strains. 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. ![]() However, the denitrification abilities of the genus as a whole remain poorly characterized. A few members of the bacterial genus Thermus have been shown to be incomplete denitrifiers, terminating with nitrite (NO 2 −) or nitrous oxide (N 2O). ![]()
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