Caulobacter flavus sp nov., a stalked bacterium isolated from rhizosphere soil

A Gram-stain-negative, aerobic, yellow-pigmented and rod-shaped bacterium with a single polar flagellum or a stalk, designated strain RHGG3(T), was isolated from rhizosphere soil of cultivated watermelon (Citrullus lanatus) collected from Hefei, China. Optimal growth of strain RHGG3(T) was observed at pH 7.0 and 28-30 degrees C. Cells were catalase-positive and oxidase-negative. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain RHGG3(T) belonged to the genus Caulobacter and showed the highest 16S rRNA gene sequence similarities to Caulobacter segnis ATCC 21756(T) (98.6 %), Caulobacter vibrioides CB51(T) (98.3 %) and Caulobacter henricii ATCC 15253(T) (97.2 %). The G +C content of the genomic DNA was 70 mol%. Strain RHGG3(T) contained Q-10 as the sole ubiquinone and the major fatty acids (>8 %) were 11-methyl C-18 : 1 omega 7c, C-18 : 1 omega 7c, C-16 : 0, C-15 : 0 and summed feature 3 (C-16 : 1 omega 7c and/or iso-C-15 : 0 2-OH). The polar lipids were various unknown glycolipids, phosphatidylglycerol and phosphoglycolipids. DNA-DNA relatedness of strain RHGG3(T) to type strains of the most closely related species (Caulobacter segnis ATCC 21756(T), Caulobacter vibrioides DSM 4738 and Caulobacter henricii ATCC 15253(T)) was 32.4-40.9 0/o. Based on polyphasic taxonomy analysis (phylogenetic, unique phenotypic traits, chemotaxonomic and DNA-DNA hybridizations), strain RHGG3(T) represents a novel species of the genus Caulobacter, for which the name Caulobacter flavus sp. nov. is proposed. The type strain is RHGG3(T) (=CGMCC 1.15093(T)=KCTC 42581(T)=JCM 30763(T)).