Microbacterium paulum sp. nov., isolated from microfiltered milk

Abstract

A novel Gram-stain-positive, strictly aerobic, short rod-shaped bacterium, designated 2CT, 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 2CT was closely related to species of the genus Microbacterium , with the highest sequence similarity (99.2 %) to Microbacterium lacticum DSM 20427T as well as Microbacterium flavum DSM 18909T (=YM18-098T). The phylogenetic tree based on 16S rRNA genes showed that strain 2CT clustered with M. flavum DSM 18909T. However, the phylogenetic tree based on concatenated 16S rRNA and four housekeeping genes showed that strain 2CT clustered with M. lacticum DSM 20427T. Furthermore, the phylogenomic tree showed that strain 2CT clustered with M. lacticum DSM 20427T and M. flavum DSM 18909T. The major respiratory quinones were MK-10, MK-11 and MK-12. The predominant cellular fatty acids were anteiso-C15 : 0, iso-C16 : 0 and anteiso-C17 : 0. The polar lipid composition of strain 2CT 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 2CT 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 2CT (=LMG 32277T=CECT 30329T) is considered to represent a new species, for which the name Microbacterium paulum sp. nov. is proposed.