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

Abstract A novel gram-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 sequences revealed that strain GXG1230T was affiliated with the genus Microbacterium. Additionally, it demonstrated a high degree of similarity to Microbacterium paludicola US15T (97.9%) and Microbacterium marinilacus YM11-607T (97.3%). Chemotaxonomic characteristics showed that the whole-cell sugars were glucose, xylose, rhamnose, galactose and malados. Menaquinones MK-11 and MK-12 were detected as respiratory quinones. Lysine was found in the peptidoglycan hydrolysate and the polar lipids were diphosphatidyl glycerol, phospholipids and unidentified glycolipid. The major fatty acids were iso-C14:0, iso-C16:0, anteiso-C15:0 and anteiso-C17:0. The strain GXG1230T exhibited a genomic DNA G + C content of 71.7%. Furthermore, the average nucleotide identity values of GXG1230T with the reference strain 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 GXG1230T is considered to represent a novel species of the genus Microbacterium, for which the name Microbacterium rhizophilus sp.nov is proposed, with GXG1230T (= MCCC 1K09223T = KCTC 59252T) as the type strain.