A Gram-stain positive actinomycete, strain AZ1-19T, isolated from roots of Azadirachta indica A. Juss. var. siamensis Valeton, collected from Chachoengsao province, Thailand, was characterised taxonomically by using a polyphasic approach. Strain AZ1-19T was found to have characteristics consistent with those of members of the genus Micromonospora. The cell wall peptidoglycan of the strain was found to contain meso-diaminopimelic acid. The predominant phospholipids were identified as diphosphatidylglycerol, phosphatidylethanolamine and phosphatidylinositol. The characteristic whole-cell sugars were identified as glucose, xylose, galactose and mannose. The major menaquinones were found to be MK-9(H6), MK-10(H6) and MK-10(H8), and the major cellular fatty acids were identified as iso-C16:0, iso-C15:0, anteiso-C15:0 and anteiso-C17:0. Comparative analysis of 16S rRNA gene sequences revealed that strain AZ1-19T is closely related to Micromonospora costi CS1-12T (98.75% similarity), Micromonospora avicenniae 268506T (98.75%), Micromonospora haikouensis 232617T (98.68%) and Micromonospora siamensis TT2-4T (98.61%), whilst the corresponding phylogenetic analysis based on partial gyrase subunit B (gyrB) gene sequences indicated that strain AZ1-19T forms a clade with M. avicenniae 268506T with a high bootstrap value. The DNA G + C content was determined to be 69.8 mol%. Moreover, a combination of DNA-DNA relatedness values and some phenotypic and chemotaxonomic properties indicated that the strain could be distinguished from closely related species. Therefore, it is considered that strain AZ1-19T represents a novel Micromonospora species for which the name Micromonospora azadirachtae sp. nov. is proposed. The type strain is AZ1-19T (= KCTC 39941T = NBRC 112784T = JCM 32148T = TISTR 2559T).
Keywords: Azadirachta indica; Endophytic actinomycetes; Micromonospora azadirachtae; Micromonosporaceae; Plant root.