Microbacterium azadirachtae sp. nov., a plant-growth-promoting actinobacterium isolated from the rhizoplane of neem seedlings

Abstract

Microbacterium strain AI-S262(T) was isolated from the rhizoplane of neem seedlings in the Botanical garden of Tamilnadu Agricultural University, Coimbatore, India, and subjected to phenotypic, chemotaxonomic and genetic characterization. Cells of this strain were Gram-stain-positive, motile, non-spore-forming, short rods and formed light-yellow-pigmented colonies on nutrient agar. Strain AI-S262(T) contained MK-12 and MK-13 as the main respiratory quinones, anteiso-C(15 : 0), anteiso-C(17 : 0) and iso-C(16 : 0) as the predominant fatty acids, peptidoglycan-type B2beta with glycolyl residues, and had a DNA G+C content of 69.5 mol%. A phylogenetic analysis based on 16S rRNA gene sequences showed 98.0-98.6 % pair-wise similarity with respect to close relatives in the genus Microbacterium. DNA-DNA hybridization experiments revealed a low level of DNA-DNA relatedness (less than 39%) between strain AI-S262(T) and its closest relatives. Data from DNA-DNA hybridization and phenotypic analyses supported the conclusion that strain AI-S262(T) represents a novel species in the genus Microbacterium, for which the name Microbacterium azadirachtae sp. nov. is proposed. The type strain is AI-S262(T) (=JCM 15681(T) =LMG 24772(T) =KCTC 19668(T)).