Helicovermis profundi gen. nov., sp. nov., a novel mesophilic, asporogenous bacterium within the Clostridia isolated from a deep-sea hydrothermal vent chimney

Abstract

A novel mesophilic bacterial strain, designated S502^T, was isolated from a deep-sea hydrothermal vent at Suiyo Seamount, Japan. Cells were Gram-positive, asporogenous, motile, and curved rods, measuring 1.6-5.6 µm in length. The strain was an obligate anaerobe that grew fermentatively on complex substrates such as yeast extract and Bacto peptone. Elemental sulfur stimulated the growth of the strain, and was reduced to hydrogen sulfide. The strain grew within a temperature range of 10-23 °C (optimum at 20 °C), pH range of 4.8-8.3 (optimum at 7.4), and a NaCl concentration range of 1.0-4.0% (w/v) (optimum at 3.0%, w/v). Phylogenetic analysis based on the 16S rRNA gene sequence revealed that the isolate was a member of the class Clostridia, with Fusibacter paucivorans strain SEBR 4211^T (91.1% sequence identity) being its closest relative. The total size of the genome of the strain was 3.12 Mbp, and a G + C content was 28.2 mol%. The highest values for average nucleotide identity (ANI), average amino acid identity (AAI), and digital DNA-DNA hybridization (dDDH) value of strain S502^T with relatives were 67.5% (with Marinisporobacter balticus strain 59.4M^T), 51.5% (with M. balticus strain 59.4M^T), and 40.9% (with Alkaliphilus serpentinus strain LacT^T), respectively. Based on a combination of phylogenetic, genomic, and phenotypic characteristics, we propose strain S502^T to represent a novel genus and species, Helicovermis profundi gen. nov., sp. nov., with the type strain S502^T (= DSM 112048^T = JCM 39167^T).

Keywords: Anaerobic; Clostridia; Deep-sea hydrothermal vent; Fermentation; Mesophile.