Aquabacterium tepidiphilum sp. nov., a moderately thermophilic bacterium isolated from a hot spring.

A Gram-stain-negative, aerobic, non-spore-forming and rod-shaped bacterium, designated YIM 730274T, was isolated from a sediment sample collected from a hot spring located in Tibet, PR China, and was characterized by using a polyphasic taxonomy approach. Cells were motile by means of a polar flagellum. The strain was oxidase- and catalase-positive, and contained polyalkanoates and polyphosphate as storage polymers. Growth occurred at 25-50 °C, at pH 6.0-8.5 and with 0.5-1.0 % NaCl. The major fatty acids (>10 %) were summed feature 3 (C16 : 1ω6c and/or C16 : 1ω7c), summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c) and C16 : 0. The known polar lipids comprised of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol and phosphatidylserine. The isoprenoid quinone was Q-8. The G+C content of genomic DNA was 70.7 mol%. The results of phylogenetic analyses based on 16S rRNA gene sequences indicated that the strain forms a monophyletic branch at the periphery of the evolutionary radiation occupied by the genus Aquabacterium in the class Betaproteobacteria. The most closely related phylogenetic neighbours were Aquabacterium limnoticumABP-4T (97.8 % 16S rRNA gene sequence identity) and Aquabacterium communeB8T (97.2 % 16SrRNA gene sequence identity). DNA-DNA relatedness values between YIM 730274T and A. limnoticum KCTC 23306T (46.4±0.4 %) and A. commune DSM 11901T (42.2±1.2 %) were well below the 70 % limit for species identification. YIM 730274T was distinguishable from other members of the genus Aquabacterium by the differences in phenotypic, chemotaxonomic and genotypic characteristics. YIM 730274T merits recognition as a representative of a novel species of the genus Aquabacterium. It is proposed that the isolate should be classified in the genus Aquabacterium as representing a novel species, Aquabacteriumtepidiphilum sp. nov. The type strain is YIM 730274T (=KCTC 52716T=CCTCC AB 2016295T).