Vestiges of Adaptation to the Mesophilic Environment in the Genome of Tepiditoga spiralis gen. nov., sp. nov.

A novel anaerobic heterotrophic strain, designated strain sy52, was isolated from a hydrothermal chimney at Suiyo Seamount in the Pacific Ocean. A 16S rRNA gene analysis revealed that the strain belonged to the family Petrotogaceae in the phylum Thermotogae. The strain was mesophilic with optimum growth at 48°C and the phylum primarily comprised hyperthermophiles and thermophiles. Strain sy52 possessed unique genomic characteristics, such as an extremely low G+C content and 6 copies of rRNA operons. Genomic analyses of strain sy52 revealed that amino acid usage in the predicted proteins resulted from adjustments to mesophilic environments. Genomic features also indicated independent adaptions to the mesophilic environment of strain sy52 and Mesotoga species, which belong to the mesophilic lineage in the phylum Thermotogae. Based on phenotypic and phylogenetic evidence, strain sy52 is considered to represent a novel genus and species in the family Petrotogaceae with the proposed name Tepiditoga spiralis gen. nov., sp. nov.