Athalassotoga saccharophila gen. nov., sp. nov., isolated from an acidic terrestrial hot spring, and proposal of Mesoaciditogales ord. nov. and Mesoaciditogaceae fam. nov. in the phylum Thermotogae.

A novel moderately thermophilic, weakly acidophilic, heterotrophic, anaerobic, short-rod bacterium having an outer sheath-like structure (toga) was isolated from a low-salt acidic terrestrial hot spring in Oku-Shiobara, Tochigi, Japan. The strain, designated NAS-01(T), grew between 30 and 60 °C (optimum 55 °C), and at pH 4.5 and 7.5 (optimum pH 5.5 to 6.0) and could not grow in media with ≥ 1 % NaCl (optimum 0 % NaCl). It utilized Fe(III), thiosulfate or l-cystine as electron acceptor for growth, and yeast extract, peptone or a variety of sugars as carbon and energy sources. The major cellular fatty acid was C16 : 0, and no lipoquinone was detected. Strain NAS-01(T) contained phospholipids and glycolipids, but not aminolipids. The DNA G+C content was 41.1 mol%. Phylogenetic analysis based on the 16S rRNA gene sequence revealed that the strain was included in the phylum Thermotogae, and was closely related to Mesoaciditoga lauensis. The 16S rRNA gene sequence similarity between them was 90 %, and they were deeply branched off the rest of the known Thermotogae species. On the basis of the phylogenetic and ecophysiological properties, strain NAS-01(T) represents a novel species of a new genus in the phylum Thermotogae, for which we propose the name Athalassotoga saccharophila gen. nov., sp. nov. The type strain of the type species is NAS-01(T) ( = JCM 19762(T) = DSM 28954(T)). In addition, we propose a new order and family, Mesoaciditogales ord. nov. and Mesoaciditogaceae fam. nov., respectively, to accommodate the novel genus and the closely related genus Mesoaciditoga.