Metagenomics Revealed a New Genus ' Candidatus Thiocaldithrix dubininis' gen. nov., sp. nov. and a New Species ' Candidatus Thiothrix putei' sp. nov. in the Family Thiotrichaceae , Some Members of Which Have Traits of Both Na + - and H + -Motive Energetics.

Two metagenome-assembled genomes (MAGs), GKL-01 and GKL-02, related to the family Thiotrichaceae have been assembled from the metagenome of bacterial mat obtained from a sulfide-rich thermal spring in the North Caucasus. Based on average amino acid identity (AAI) values and genome-based phylogeny, MAG GKL-01 represented a new genus within the Thiotrichaceae family. The GC content of the GKL-01 DNA (44%) differed significantly from that of other known members of the genus Thiothrix (50.1-55.6%). We proposed to assign GKL-01 to a new species and genus ' Candidatus Thiocaldithrix dubininis' gen. nov., sp. nov. GKL-01. The phylogenetic analysis and estimated distances between MAG GKL-02 and the genomes of the previously described species of the genus Thiothrix allowed assigning GKL-02 to a new species with the proposed name ' Candidatus Thiothrix putei' sp. nov. GKL-02 within the genus Thiothrix . Genome data first revealed the presence of both Na + -ATPases and H + -ATPases in several Thiothrix species. According to genomic analysis, bacteria GKL-01 and GKL-02 are metabolically versatile facultative aerobes capable of growing either chemolithoautotrophically or chemolithoheterotrophically in the presence of hydrogen sulfide and/or thiosulfate or chemoorganoheterotrophically.