Rhodococcus pedocola sp nov and Rhodococcus humicola sp nov., two antibiotic-producing actinomycetes isolated from soil

Two novel actinobacterial strains, UC12(T) and UC33(T), were isolated from forest topsoil in Suwon, Gyeonggi-Do, South Korea. Comparative analysis of nearly full-length 16S rRNA gene sequences of UC12(T) and UC33(T) revealed close pairwise similarity with species of the genus Rhodococcus, and the UC12(T) and UC33(T) sequences were most closely related to Rhodococcus canchipurensis MBRL 353(T) (98.91 % 16S rRNA gene sequence similarity) and Rhodococcus triatomae IMMIB RIV-085(T) (97.71 %), respectively. DNA DNA hybridization showed 33.05-35.60 % genomic similarity between strains UC12(T) and UC33(T), while strain UC12(T) shared DNA-DNA relatedness values of 32.71-41.29 % with the closest species of the genus Rhodococcus and strain UC33(T) shared 29.12-37.91 % genomic relatedness with the closest species of the genus Rhodococcus. Both strains showed similar chemotaxonomic characteristics. The major fatty acids were C-16:0, summed feature 3, C-18:1 omega 9c and C-18:0 10 -methyl. The polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol and phosphatidylinositol mannoside. The major quinone derived was MK-8(H-2). The cell-wall peptidoglycan contained meso-diaminopimelic acid, and galactose, glucose, arabinose and ribose were detected in whole cells. Mycolic acids were detected. The DNA G+C content of strains UC12(T) and UC33(T) was 72.7 mol% and 68.8 mol%, respectively. Both strains produced antibiotic(s) that inhibited bacterial pathogens but not fungi. Based on the physiological, biochemical and genotypic features and the DNA DNA hybridization between the isolates and type strains of closely related species, we propose that these bacteria be classified as novel species of the genus Rhodococcus with the names Rhodococcus pedocola sp. nov. (type strain UC12(T)=KACC 18499(T)=NBRC 111580(T)) and Rhodococcus humicola sp. nov. (type strain UC33(T)=KACC 18500(T)=NBRC 111581(T)).