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 F4T, 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 F4T was able to hydrolyse polysaccharides such as cellulose, xylan, chitin and starch. The G+C content in the DNA of strain F4T was 52.5 mol%. The major fatty acid was iso-C17 : 0 and the major menaquinone was MK-9 (H2). The cell wall of strain F4T 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 F4T belongs to the genus Thermosporothrix, and that it was related most closely to Thermosporothrix hazakensis SK20-1T (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 F4T is considered to represent a novel species, Thermosporothrix narukonensis sp. nov. The type strain is F4T(=NBRC 111777T=BCCM/LMG 29329T).