Chthonobacter rhizosphaerae sp. nov., a bacterium isolated from rhizosphere soil of Citrus sinenesis

A Gram-staining negative, facultative anaerobic, motile and short rod-shaped bacterium, designated strain yh7-1^T, was isolated from rhizosphere soil of Citrus sinenesis collected from the garden of Citrus sinenesis in Ailao Mountain, south-west China. Cells grew at 15-45 °C, pH 5.0-9.0 and were able to tolerate up to 1% (w/v) NaCl on R2A medium. The respiratory lipoquinone was Q-10 and the major cellular fatty acids contained summed feature 8 (C_18:1 ω7c or C_18:1 ω6c) and C_18:0. Polar lipids in the cellular membrane were phosphatidylcholine, phosphatidylglycerol, phosphatidylethanolamine, two unidentified phospholipids and one unidentified aminophospholipid. The genomic DNA G+C content was 69.9 mol%. On basis of 16S rRNA gene sequence analysis, strain yh7-1^T showed the highest similarities with Chthonobacter albigriseus KCTC 42450^T (97.6%), Mongoliimonas terrestris KCTC 42635^T (97.0%) and lower than 97.0% to other species. Phylogenetic trees based on 16S rRNA gene sequences indicated that strain yh7-1^T clustered with C. albigriseus KCTC 42450^T. The ANI values ranged between 78.1 and 82.7% for C. albigriseus KCTC 42450^T, M. terrestris KCTC 42635^T and strain yh7-1^T, which were lower than the prokaryotic species delineation threshold of 95.0-96.0%. The digital DNA-DNA hybridization values between C. albigriseus KCTC 42450^T, M. terrestris KCTC 42635^T and strain yh7-1^T indicated that the new isolate represents a novel genomic species. According to the phenotypic and genotypic characteristics, strain yh7-1^T should belong to the genus Chthonobacter, for which the name Chthonobacter rhizosphaerae sp. nov. (type strain yh7-1^T = CGMCC 1.17236^T = CCTCC AB 2019258^T = KCTC 82185^T) is proposed.