Rhodococcus gannanensis sp. nov., a novel endophytic actinobacterium isolated from root of sunflower (Helianthus annuus L.).

A novel Gram-positive, aerobic, non-motile strain, designated strain M1, was isolated from sunflower root (Helianthus annuus L.) and characterised using a polyphasic taxonomic approach. The morphological and chemotaxonomic properties of the isolate were typical of those of members of the genus Rhodococcus. Phylogenetic analyses based on 16S rRNA gene sequence showed that strain M1 belongs to the genus Rhodococcus and clustered with Rhodococcus canchipurensis MBRL 353 (99.1%, sequence similarity) and Rhodococcus pedocola UC12 (98.7%). However, the DNA-DNA hybridizations between strain M1 and R. canchipurensis MBRL 353 and R. pedocola UC12 were found to be 52.8 ± 0.7 and 41.8 ± 0.2%, respectively. The optimal growth temperature and pH for strain M1 was found to be at 28 °C and at pH 7.0. The peptidoglycan was found to contain meso-diaminopimelic acid; galactose, glucose and arabinose were detected as diagnostic sugars. The main polar lipids were identified as diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol and phosphatidylinositol mannoside; MK-8(H) was found to be the dominant menaquinone. The major fatty acids were identified as C, 10-methyl C and C ω9c. Mycolic acids were found to be present. The G+C content of the genomic DNA was determined to be 69.5 mol%. Based on a comparative analysis of phenotypic and genotypic characteristics, in combination with DNA-DNA hybridization results, the isolate is concluded to represent a novel species of the genus Rhodococcus, for which the name Rhodococcus gannanensis sp. nov. is proposed. The type strain is M1 (=CGMCC 1.15992 = DSM 104003).