Microbacterium paulum sp. nov., isolated from microfiltered milk

Abstract

A novel Gram-stain-positive, strictly aerobic, short rod-shaped bacterium, designated 2C^T, was isolated from freshly packaged microfiltered milk. This strain was able to grow within the NaCl concentration range of 0-5 % (w/v), temperature range of 8-37 °C (optimally at 30 °C) and at pH 6.0-10.0. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain 2C^T was closely related to species of the genus Microbacterium, with the highest sequence similarity (99.2 %) to Microbacterium lacticum DSM 20427^T as well as Microbacterium flavum DSM 18909^T (=YM18-098^T). The phylogenetic tree based on 16S rRNA genes showed that strain 2C^T clustered with M. flavum DSM 18909^T. However, the phylogenetic tree based on concatenated 16S rRNA and four housekeeping genes showed that strain 2C^T clustered with M. lacticum DSM 20427^T. Furthermore, the phylogenomic tree showed that strain 2C^T clustered with M. lacticum DSM 20427^T and M. flavum DSM 18909^T. The major respiratory quinones were MK-10, MK-11 and MK-12. The predominant cellular fatty acids were anteiso-C_{15 : 0}, iso-C_{16 : 0} and anteiso-C_{17 : 0}. The polar lipid composition of strain 2C^T consisted of diphosphatidylglycerol, phosphatidylglycerol, three unidentified glycolipids and two unidentified lipids. The cell-wall peptidoglycan type was a variant of B1α {Gly} [l-Lys] d-Glu-l-Lys, with the amino acids lysine, glycine, alanine and glutamic acid. The whole-cell sugars consisted of galactose, glucose, ribose and minor amounts of rhamnose. In addition, strain 2C^T showed a glycolyl-type cell wall. The genomic DNA G+C content was 69.8mol%, while the average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values with the closely related Microbacterium species were below the recognized thresholds of 95-96 % ANI and 70 % DDH for species definition. Based on the phenotypic and genotypic data, strain 2C^T (=LMG 32277^T=CECT 30329^T) is considered to represent a new species, for which the name Microbacterium paulum sp. nov. is proposed.

Keywords: Microbacteriaceae; Microbacterium paulum; microfiltered milk.