Microbacterium tumbae sp. nov., an actinobacterium isolated from the stone chamber of ancient tumulus

Eight strains characterised as Gram-stain-positive, non-spore-forming and non-motile rods were isolated from samples collected from stone chambers of the Takamatsuzuka and Kitora tumuli in Asuka village, Nara Prefecture, Japan. Among them, one strain, T7528-3-6bT, was shown to form a novel lineage within the genus Microbacterium. The most closely phylogenetically related species to T7528-3-6bT was Microbacterium panaciterrae, with 97.8 % sequence similarity. The major isoprenoid quinones of T7528-3-6bT were MK-12, MK-13 and MK-11. The predominant cellular fatty acids for this isolate were anteiso-C15 : 0, anteiso-C17 : 0, iso-C16 : 0 and iso-C15 : 0. The diagnostic diamino acid of the peptidoglycan of this isolate was ornithine. Major polar lipids of the isolate were phosphatidylglycerol, diphosphatidylglycerol and an unknown glycolipid. The G+C content of the genomic DNA of this isolate was 70.1 mol%. On the basis of the results of physiological, biochemical and chemotaxonomic tests and molecular phylogenetic analysis, T7528-3-6bT is considered to represent a novel species of the genus Microbacterium, for which the name M. tumbae sp. nov. has been proposed. The type strain is T7528-3-6bT (=JCM 28836T=NCIMB 15039T). The results of comparisons of both phenotypic and genotypic (16S rRNA gene sequence) characteristics indicated that the remaining seven isolates were very closely related to Microbacterium shaanxiense. Although the sequence similarity between the two was 99.2 %, further detailed multifaceted comparisons are needed to determine their accurate taxonomic assignment.