Bacillus thermolactis sp. nov., isolated from dairy farms, and emended description of Bacillus thermoamylovorans

Abstract

A polyphasic taxonomic study was performed on 22 thermotolerant, aerobic, endospore-forming bacteria from dairy environments. Seventeen isolates were retrieved from raw milk, one from a filter cloth and four from grass, straw or milking equipment. These latter four isolates (R-6546, R-7499, R-7764 and R-7440) were identified as Bacillus thermoamylovorans based on DNA–DNA hybridizations (values above 70 % with Bacillus thermoamylovorans LMG 18084T) but showed discrepancies in characteristics with the original species description, so an emended description of this species is given. According to 16S rRNA gene sequence analysis and DNA–DNA hybridization experiments, the remaining 18 isolates (R-6488T, R-28193, R-6491, R-6492, R-7336, R-33367, R-6486, R-6770, R-31288, R-28160, R-26358, R-7632, R-26955, R-26950, R-33520, R-6484, R-26954 and R-7165) represented one single species, most closely related to Bacillus thermoamylovorans (93.9 % 16S rRNA gene sequence similarity), for which the name Bacillus thermolactis is proposed. Cells were Gram-stain-positive, facultatively anaerobic, endospore-forming rods that grew optimally at 40–50 °C. The cell wall peptidoglycan type of strain R-6488T, the proposed type strain, was A1γ based on meso-diaminopimelic acid. Major fatty acids of the strains were C16 : 0 (28.0 %), iso-C16 : 0 (12.1 %) and iso-C15 : 0 (12.0 %). MK-7 was the predominant menaquinone, and major polar lipids were diphosphatidylglycerol, phosphatidylglycerol and some unidentified phospholipids. DNA G+C content was 35.0 mol%. Phenotypic properties allowed discrimination from other thermotolerant species of the genus Bacillus and supported the description of the novel species Bacillus thermolactis, with strain R-6488T ( = LMG 25569T  = DSM 23332T) as the proposed type strain.