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 RHGG3T, was isolated from rhizosphere soil of cultivated watermelon (Citrullus lanatus) collected from Hefei, China. Optimal growth of strain RHGG3T was observed at pH 7.0 and 28-30 °C. Cells were catalase-positive and oxidase-negative. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain RHGG3T belonged to the genus Caulobacter and showed the highest 16S rRNA gene sequence similarities to Caulobacter segnis ATCC 21756T (98.6 %), Caulobacter vibrioides CB51T (98.3 %) and Caulobacter henricii ATCC 15253T (97.2 %). The G+C content of the genomic DNA was 70 mol%. Strain RHGG3T contained Q-10 as the sole ubiquinone and the major fatty acids (>8 %) were 11-methyl C18 : 1ω7c, C18 : 1ω7c, C16 : 0, C15 : 0 and summed feature 3 (C16 : 1ω7c and/or iso-C15 : 0 2-OH). The polar lipids were various unknown glycolipids, phosphatidylglycerol and phosphoglycolipids. DNA-DNA relatedness of strain RHGG3T to type strains of the most closely related species (Caulobacter segnis ATCC 21756T, Caulobacter vibrioides DSM 4738 and Caulobacter henricii ATCC 15253T) was 32.4-40.9 %. Based on polyphasic taxonomy analysis (phylogenetic, unique phenotypic traits, chemotaxonomic and DNA-DNA hybridizations), strain RHGG3T represents a novel species of the genus Caulobacter, for which the name Caulobacter flavus sp. nov. is proposed. The type strain is RHGG3T ( = CGMCC 1.15093T = KCTC 42581T = JCM 30763T).