Microbacterium aquilitoris sp. nov. and Microbacterium gwkjiense sp. nov., isolated from beach

Abstract

Three Gram-reaction-positive bacterial strains, designated KSW-18^T, KSW2-22, and KSW4-11^T, were isolated from seawater, and two dried seaweed samples collected at Gwakji Beach in Jeju, Republic of Korea, respectively, and their taxonomic positions were examined by a polyphasic approach. The 16S rRNA gene phylogeny showed that strain KSW4-11^T was tightly associated with Microbacterium oleivorans NBRC 103075^T, while strains KSW-18^T and KSW2-22 formed a distinctive subline at the base of a clade including the above two strains. The three isolates showed high sequence similarity with one another (99.7-99.9%; 1-4 nt differences) and Microbacterium oleivorans (99.8-99.9%; 1-3 nt differences). The chemotaxonomic features were typical for the genus Microbacterium; Lysine as the diagnostic diamino acid and N-glycolylated muramic acid of the peptidoglycans, the predominant menaquinones of MK-11, MK-10 and MK-12, the major fatty acids of anteiso-C_15:0 and anteiso-C_17:0, and the major polar lipids including diphosphatidylglycerol, phosphatidylglycerol, and two or three unidentified glycolipids. In core genome-based phylogenetic tree, strains KSW-18^T and KSW2-22 were closely associated with Microbacterium oleivorans NBRC 103075^T, while strain KSW4-11^T formed a distinctive subline at the base of a clade including the above three strains, in contrast to the 16S rRNA gene tree. Strains KSW-18^T and KSW2-22 shared an OrthoANIu of 98.6% and a digital DNA-DNA hybridization of 87.6% with each other, representing that they were strains of a species, while the OrthoANIu and digital DNA-DNA hybridization values between strains KSW-18^T and KSW4-11^T, and between both of these isolates and all members of the genus Microbacterium were ≤86.5% and ≤30.7%, respectively. The analyses of overall genomic relatedness indices and phenotypic distinctness support that the three isolates represent two new species of the genus Microbacterium. Based on the results obtained here, Microbacterium aquilitoris sp. nov. (type strain KSW-18^T = KCTC 49623^T = NBRC 115222^T) and Microbacterium gwkjiense sp. nov. (type strain KSW4-11^T = KACC 23321^T = DSM 116380^T) are proposed.

Keywords: Genome analysis; Seawater; Seaweed; Two Microbacterium species.