Rhodobacter thermarum sp. nov., a novel phototrophic bacterium isolated from sediment of a hot spring

An ovoid to rod-shaped, phototrophic, purple non-sulfur bacterium was isolated from a sediment sample of a hot spring in Tibet, China. Cells of strain YIM 73036ᵀ were Gram-stain negative, non-motile and multiplied by binary fission. Strain YIM 73036ᵀ grew optimally at pH 7.0–7.5 at 37–45 °C. Growth occurred in 0.5–3.5% (w/v) NaCl. Vitamins were not required for growth. The presence of photosynthesis genes pufL and pufM were shown and photosynthesis pigments were formed. Bacteriochlorophyll α, the bacteriopheophytin and carotenoids were present as photosynthetic pigments. Internal cytoplasmic membranes were of the lamellar type. The organism YIM 73036ᵀ was able to grow chemo-organoheterophically, chemo-lithoautotrophically and photo-organoheterotrophically but photo-lithoautotrophic and fermentative growth were not demonstrated. Phylogenetic analysis on the basis of 16S rRNA gene sequences showed that strain YIM 73036ᵀ is closely related to Rhodobacter blasticus ATCC 33485ᵀ (96.65% sequence similarity) and clustered with species of the genus Rhodobacter of the family Rhodobacteraceae. Whole-genome sequence analyses based on the average nucleotide BLAST identity (ANI < 82%) indicated that this isolate belongs to a novel species. The genomic DNA G+C content of organism YIM 73036ᵀ was determined to be 66.0 mol%. Strain YIM 73036ᵀ contained Q-10 as the predominant ubiquinone and C₁₈:₁ω7c, C₁₈:₁ω7c 11-methyl and C₁₈:₀ as the major fatty acids. The major polar lipids were phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine and unidentified phospholipid. Differential phenotypic and chemotaxonomic properties, together with the phylogenetic distinctiveness, demonstrated that strain YIM 73036ᵀ is distinguishable from other species of the genus Rhodobacter. On the basis of the data presented, strain YIM 73036ᵀ is considered to represent a novel species of the genus Rhodobacter, for which the name Rhodobacter thermarum sp. nov. [type strain YIM 73036ᵀ (= KCTC 52712ᵀ = CCTCC AB 2016298ᵀ)] is proposed.