Abstract
A novel bacterium, strain EPR55-1T, was isolated from a deep-sea hydrothermal vent on the East Pacific Rise. The cells were motile rods. Growth was observed at temperatures between 50 and 60°C (optimum, 60°C), at pH values between 5.4 and 8.6 (optimum, pH 6.6) and in the presence of 2.4–3.2% (w/v) NaCl (optimum, 2.4%). The isolate used molecular hydrogen as its sole electron donor, carbon dioxide as its sole carbon source, ammonium as its sole nitrogen source, and thiosulfate, sulfite (0.01 to 0.001%, w/v) or elemental sulfur as its sole sulfur source. Nitrate, nitrous oxide (33%, v/v), thiosulfate, molecular oxygen (0.1%, v/v) or elemental sulfur could serve as the sole electron acceptor to support growth. Phylogenetic analyses based on both 16S rRNA gene sequences and whole genome sequences indicated that strain EPR55-1T belonged to the family Nitratiruptoraceae of the class “Campylobacteria”, but it had the distinct phylogenetic relationship with the genus Nitratiruptor. On the basis of the physiological and molecular characteristics of the isolate, the name Nitrosophilus alvini gen. nov. sp. nov. is proposed, with EPR55-1T as the type strain (= JCM 32893T = KCTC 15925T). In addition, it is shown that “Nitratiruptor labii” should be transferred to the genus Nitrtosophilus; the name Nitrosophilus labii comb. nov. (JCM 34002T = DSM 111345T) is proposed for this organism. Furthermore, 16S rRNA gene-based and genome-based analyses showed that Cetia pacifica is phylogenetically associated with Caminibacter species. We therefore propose the reclassification of Cetia pacifica as Caminibacter pacificus comb. nov. (DSM 27783T = JCM 19563T). Additionally, AAI thresholds for genus classification and the reclassification of subordinate taxa within “Campylobacteria” are also evaluated, based on the analyses using publicly available genomes of all the campylobacterial species.
Highlights
The phylum “Campylobacterota” is a phylogenetically and ecophysiologically diverse bacterial group that consists of two classes, i.e., Desulfurellia and “Campylobacteria” [1]
While this phylum is widely recognized as a group including pathogenic microorganisms, e.g. Helicobacter pylori and Campylobacter jejuni, and many studies have focused on these pathogens [2, 3], an ever expanding number of non-pathogenic species have been identified which thrive as mesophiles or thermophiles in a wide range of natural environments [4] where they are recognized as important players in biogeochemical cycles [1, 5]
Temperature, pH, and NaCl ranges for growth of strain EPR55-1T were similar to those of “Nitratiruptor labii” HRV44T [9] (Table 1)
Summary
The phylum “Campylobacterota” is a phylogenetically and ecophysiologically diverse bacterial group that consists of two classes, i.e., Desulfurellia (the former order Desulfurellales) and “Campylobacteria” (the former class Epsilonproteobacteria) [1] While this phylum is widely recognized as a group including pathogenic microorganisms, e.g. Helicobacter pylori and Campylobacter jejuni, and many studies have focused on these pathogens [2, 3], an ever expanding number of non-pathogenic species have been identified which thrive as mesophiles or thermophiles in a wide range of natural environments (e.g., deep-sea hydrothermal fields, stratified ocean, terrestrial sulfidic caves, and oil fields) [4] where they are recognized as important players in biogeochemical cycles [1, 5]. This leaves the classification of thermophiles unresolved as almost all thermophilic families are composed of only a single genus, which were mostly retrieved from deepsea hydrothermal vents
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