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 degrees 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 omega 7c or C-18:1 omega 6c) 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.

Automated summary

The bacterium yh7-1(T) isolated from the rhizosphere soil of Citrus sinenesis in southwest China may belong to a novel genomic species Chthonobacter rhizosphaerae. It demonstrates growth at temperatures as low as 15 degrees Celsius and tolerates NaCl concentration up to 1%, with a unique phospholipid fatty acid composition.