Thermosporothrix narukonensis sp. nov., belonging to the class Ktedonobacteria, isolated from fallen leaves on geothermal soil, and emended description of the genus Thermosporothrix

A thermophilic, Gram-stain-positive, spore-forming bacterium that formed branched vegetative and aerial mycelia was isolated from fallen leaves on geothermal soil. This strain, designated F4^T, grew at temperatures between 30 and 60°C; optimum growth temperature was 50°C, whereas no growth was observed below 28°C or above 65°C. The pH range for growth was 4.9–9.5; the pH for optimum growth was 7.0, but no growth was observed at pH below 4.4 or above 10.0. Strain F4^T was able to hydrolyse polysaccharides such as cellulose, xylan, chitin and starch. The G+C content in the DNA of strain F4^T was 52.5 mol%. The major fatty acid was iso-C_{17: 0} and the major menaquinone was MK-9 (H₂). The cell wall of strain F4^T contained glutamic acid, serine, glycine, alanine and ornithine in a molar ratio of 1.0:1.5:1.4:1.8:0.7. The polar lipids of this strain consisted of phosphatidylglycerol, diphosphatidylglycerol, phosphatidylinositol, one unknown phospholipid, three unknown glycolipids and two unknown lipids. The cell-wall sugar was mannose. Detailed phylogenetic analysis based on 16S rRNA gene sequences indicated that strain F4^T belongs to the genus Thermosporothrix, and that it was related most closely to Thermosporothrix hazakensis SK20-1^T (98.7 % similarity). DNA–DNA hybridization showed relatedness values of less than 15 % with the type strain of Thermosporothrix hazakensis. On the basis of phenotypic features and phylogenetic position, strain F4^T is considered to represent a novel species, Thermosporothrix narukonensis sp. nov. The type strain is F4^T(=NBRC 111777^T=BCCM/LMG 29329^T).