Microbacterium rhizophilus sp. nov., an indole acetic acid-producing actinobacterium isolated from rhizosphere soil

A novel gram-stain-positive, short rod, aerobic, non-motile and non-spore-forming actinobacterial strain, designated GXG1230T was isolated from the rhizosphere soil of a coastal mangrove forest in Beihai city, Guangxi Zhuang Autonomous Region, PR China. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain GXG1230(T) was affiliated with the genus Microbacterium. Additionally, it demonstrated a high degree of similarity to Microbacterium paludicola US15(T )(97.9%) and Microbacterium marinilacus YM11-607(T) (97.3%). Chemotaxonomic characteristics showed that the whole-cell sugars were glucose, xylose, rhamnose and galactose. Menaquinones MK-11 and MK-12 were detected as respiratory quinones. Lysine was found in the peptidoglycan hydrolysate and the polar lipids were diphosphatidylglycerol, one phospholipid and two unidentified glycolipid. The major fatty acids were anteiso-C15:0, iso-C16:0 and anteiso-C17:0. The strain GXG1230(T) exhibited a genomic DNA G + C content of 71.7%. Furthermore, the average nucleotide identity values of GXG1230(T) with the reference strains were 75.4% and 81.9%, respectively, while the digital DNA-DNA hybridization values were 20.1% and 25.0%. Based on physiological, chemotaxonomic and phylogenetic information, strain GXG1230(T )is considered to represent a novel species of the genus Microbacterium, for which the name Microbacterium rhizophilus sp.nov is proposed, with GXG1230(T) (= MCCC 1K09302(T) = KCTC 59252(T)) as the type strain.