Microbacterium immunditiarum sp. nov., an actinobacterium isolated from landfill surface soil, and emended description of the genus Microbacterium

Abstract

A Gram-positive, non-endospore-forming bacterium, designated strain SK 18(T), was isolated from surface soil of a landfill site by dilution plating on trypticase soy broth agar. Preliminary characterization of strain SK 18(T) via biochemical tests, analysis of fatty acid methyl esters and partial 16S rRNA gene sequencing placed it within the genus Microbacterium. Analysis of the cell wall indicated that the peptidoglycan was of cross-linkage type B, containing the amino acids lysine and ornithine and with muramic acid in the N-glycolyl form. The polar lipids were phosphatidylglycerol, diphosphatidylglycerol, an unidentified phospholipid and an unidentified glycolipid. The major fatty acids of the cell membrane were anteiso-C(17 : 0), anteiso-C(15 : 0) and iso-C(16 : 0). These data further strengthened placement of the strain within the genus Microbacterium. Strain SK 18(T) shared highest 16S rRNA gene sequence similarity (97.2 %) with Microbacterium ulmi DSM 16931(T). Levels of similarity with the type strains of all other recognized Microbacterium species were less than 97.0 %. DNA-DNA hybridization experiments with strain SK 18(T) and its closest relative, M. ulmi DSM 16931(T), revealed a low reassociation value of 39.0 % (σ = 3.8 %). Moreover, strain SK 18(T) showed a number of differences in phenotypic characteristics (colony colour, catalase activity, hydrolysis of polymers, acid production from sugars and oxidation of various substrates), and its DNA G+C content was also higher than that of M. ulmi DSM 16931(T). These data indicated that strain SK 18(T) represents a novel species of the genus Microbacterium, for which the name Microbacterium immunditiarum sp. nov. is proposed. The type strain is SK 18(T) (= MTCC 7185(T) = JCM 14034(T)). An emended description of the genus Microbacterium is also provided.