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 GXG1230 T 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-C 15:0 , iso-C 16:0 and anteiso-C 17:0 . 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.