Nocardioides ultimimeridianus sp. nov. and Nocardioides maradonensis sp. nov., isolated from rhizosphere soil

Abstract

Two novel Gram-reaction-positive, rod-shaped actinobacterial strains, designated RP-B26T and RP-B30T, were isolated from rhizosphere soil of a cliff-associated plant (Peucedanum japonicum Thunb.) which was collected from Mara Island, Republic of Korea. The colonies of the isolates were circular, smooth, convex and moderately yellow–light-yellow in colour. 16S rRNA gene sequence analysis revealed that the isolates belonged to the family Nocardioidaceae and formed two distinct sublineages within the radiation of the genus Nocardioides. 16S rRNA gene sequence similarity between the isolates was 98.2 %. The closest phylogenetic neighbours of strain RP-B26T were Nocardioides humi DCY24T and Nocardioides kongjuensis A2-4T with 97.4 and 97.0 % 16S rRNA gene sequence similarity, respectively, whereas 16S rRNA gene sequence similarities between strain RP-B30T and N. humi DCY24T and N. kongjuensis A2-4T were 96.5 and 96.0 %, respectively. Both of the isolates contained ll-diaminopimelic acid as the diagnostic diamino acid in the cell walls. The predominant menaquinone was MK-8(H4). The polar lipids were phosphatidylinositol and phosphatidylglycerol. The fatty acid profiles of the isolates were characterized by the presence of saturated, unsaturated, 10-methyl and hydroxyl fatty acids, with small amounts of branched fatty acids. The DNA G+C contents of strains RP-B26T and RP-B30T were 73.0 and 71.7 mol%, respectively. Levels of DNA–DNA relatedness between the isolates were 44.9±1.5 % (thermal renaturation method) and 43.2 % (photobiotin-labelled method); the isolates showed low DNA–DNA relatedness values (<11 %) to the most closely related strain, N. humi KCTC 19265T. On the basis of the phenotypic, genotypic and DNA–DNA hybridization data presented here, the isolates are considered to represent two novel species of the genus Nocardioides, for which the names Nocardioides ultimimeridianus sp. nov. (type strain RP-B26T  = KCTC 19368T  = DSM 19768T) and Nocardioides maradonensis sp. nov. (type strain RP-B30T  = KCTC 19384T  = DSM 19769T) are proposed.