Thermus caldilimi sp. nov., a thermophilic bacterium isolated from a geothermal area.

A Gram-stain negative, aerobic bacterium, designated strain YIM 78456T, was isolated from a hot spring sediment, Ngamring county, Tibet, south-west China. The taxonomic position of the isolate was investigated by a polyphasic approach. The novel isolate was found to be aerobic and rod-shaped. Colonies were observed to be pale yellow and circular. The strain was found to grow at pH 7.0-8.0 (optimum, pH 7.0), 45-65 °C (optimum, 55 °C) and in the presence of up to 1.5% NaCl. Comparison of the 16S rRNA gene sequence of strain YIM 78456T and other members of the genus Thermus showed sequence similarities ranging from 90.3 to 97.3%, with strain YIM 78456T showing close sequence similarity to Thermus caliditerrae YIM 77925T (97.3%). The phylogenetic trees based on 16S rRNA gene sequences showed that strain YIM 78456T forms a distinct clade with T. caliditerrae YIM 77925T. The predominant menaquinone was identified as MK-8 and the DNA G+C content was determined to be 65.1 mol%. The major cellular fatty acids (> 10%) were identified as iso-C15:0, anteiso-C15:0 and iso-C17:0. The polar lipids were found to consist of an aminophospholipid, a phospholipid and glycolipids. On the basis of the morphological and chemotaxonomic characteristics, as well as genotypic data, it is proposed that strain YIM 78456T represents a novel species of the genus Thermus, for which the name Thermus caldilimi sp. nov. is proposed. The type strain is YIM 78456T (= KCTC 52948T = NBRC 113036T).