Thermus caldifontis sp nov., a thermophilic bacterium isolated from a hot spring

A thermophilic bacterial strain, designated YIM 73026(T) was isolated from a sediment sample collected from a hot spring in Tibet, PR China. The taxonomic position of the novel isolate was investigated by a polyphasic approach. The novel isolate was Gram-stain-negative, aerobic and rod-shaped. Colonies were circular, convex, opaque and yellow. The strain grew at 5070 degrees C (optimum, 60 degrees C), pH 6.0-8.0 (optimum, pH 7.0) and in the presence of up to 1.0% NaCl (w/v). Comparison of the 16S rRNA gene sequences of YIM 73026(T) and those of other members of the genus Thermus showed sequence similarities ranging from 91.2 to 97.5 %, with YIM 73026(T) showing closest sequence similarity to Thermus scotoductus SE-1(T) (97.5 %). DNA-DNA hybridization results, however, revealed that DNA-DNA reassociation values between YIM 73026(T) and T. scotoductus DSM 8553(T) (37.6 %), Thermus amyloliquefaciens YIM 77409(T) (34.5 %), Thermus antranikianii DSM 12462(T) (30.3 %), Thermus caliditerrae YIM 77925(T) (28.6 %) and Thermus tengchongensis YIM 77924(T) (27.3 %) were well below the 70% limit for species identification. YIM 73026(T) contained MK-8 as the respiratory quinone, and iso-C-15:0, iso-C-16:0, iso-C-17:0 and anteiso-C-15:0 as the major cellular fatty acids (> 10 %). The polar lipids consisted of one aminophospholipid, one phospholipid and two glycolipids. The genomic DNA G+C content of YIM 73026(T) was 65.4 mol%. On the basis of morphological, chemotaxonomic and genotypic characteristics, it is proposed that the isolate represents a novel species of the genus Thermus, for which the name Thermus caldifontis sp. nov. is proposed. The type strain is YIM 73026(T) (= NBRC 112415(T) = CCTCC AB 2016305