Desulfomarina profundi gen. nov., sp. nov., a novel mesophilic, hydrogen-oxidizing, sulphate-reducing chemolithoautotroph isolated from a deep-sea hydrothermal vent chimney

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

A novel mesophilic bacterial strain, designated S502T, 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 4211T (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 S502T with relatives were 67.5% (with Marinisporobacter balticus strain 59.4MT), 51.5% (with M. balticus strain 59.4MT), and 40.9% (with Alkaliphilus serpentinus strain LacTT), respectively. Based on a combination of phylogenetic, genomic, and phenotypic characteristics, we propose strain S502T to represent a novel genus and species, Helicovermis profundi gen. nov., sp. nov., with the type strain S502T (= DSM 112048T = JCM 39167T).

Pyrofollis japonicus gen. nov. sp. nov., a novel member of the family Pyrodictiaceae isolated from the Iheya North hydrothermal field

A novel hyperthermophilic, heterotrophic archaeon, strain YC29T, was isolated from a deep-sea hydrothermal vent in the Mid-Okinawa Trough, Japan. Cells of strain YC29T were non-motile, irregular cocci with diameters of 1.2-3.0 µm. The strain was an obligatory fermentative anaerobe capable of growth on complex proteinaceous substrates. Growth was observed between 85 and 100 °C (optimum 90-95 °C), pH 4.9-6.4 (optimum 5.1), and in the presence of 1.4-4.0% (w/v) NaCl (optimum 3.0%). Inorganic carbon was required as a carbon source. Phylogenetic analysis based on the 16S rRNA gene sequence revealed that the isolate was a member of the family Pyrodictiaceae. The genome size was 2.02 Mbp with a G+C content of 49.4%. The maximum values for average nucleotide identity (ANI), average amino acid identity (AAI), and in silico DNA-DNA hybridization (dDDH) value of strain YC29T with relatives were 67.9% (with Pyrodictium abyssi strain AV2T), 61.1% (with Pyrodictium occultum strain PL-19T), and 33.8% (with Pyrolobus fumarii strain 1AT), respectively. Based on the phylogenetic, genomic, and phenotypic characteristics, we propose that strain YC29T represents a novel genus and species, Pyrofollis japonicus gen. nov., sp. (type strain YC29T = DSM 113394T = JCM 39171T).

Physiological and comparative proteomic characterization of Desulfolithobacter dissulfuricans gen. nov., sp. nov., a novel mesophilic, sulfur-disproportionating chemolithoautotroph from a deep-sea hydrothermal vent

In deep-sea hydrothermal environments, inorganic sulfur compounds are important energy substrates for sulfur-oxidizing, -reducing, and -disproportionating microorganisms. Among these, sulfur-disproportionating bacteria have been poorly understood in terms of ecophysiology and phylogenetic diversity. Here, we isolated and characterized a novel mesophilic, strictly chemolithoautotrophic, diazotrophic sulfur-disproportionating bacterium, designated strain GF1T, from a deep-sea hydrothermal vent chimney at the Suiyo Seamount in the Izu-Bonin Arc, Japan. Strain GF1T disproportionated elemental sulfur, thiosulfate, and tetrathionate in the presence of ferrihydrite. The isolate also grew by respiratory hydrogen oxidation coupled to sulfate reduction. Phylogenetic and physiological analyses support that strain GF1T represents the type strain of a new genus and species in the family Desulfobulbaceae, for which the name Desulfolithobacter dissulfuricans gen. nov. sp. nov. is proposed. Proteomic analysis revealed that proteins related to tetrathionate reductase were specifically and abundantly produced when grown via thiosulfate disproportionation. In addition, several proteins possibly involved in thiosulfate disproportionation, including those encoded by the YTD gene cluster, were also found. The overall findings pointed to a possible diversity of sulfur-disproportionating bacteria in hydrothermal systems and provided a refined picture of microbial sulfur disproportionation.