Purpose: The purpose of this study was to evaluate the genetic variation of Paenibacillus spp. isolates in relation to their ability to grow at cold temperatures (6°C) in dairy products.
Methods: Twenty-eight P. odorifer group strains isolated from fluid milk were selected based on unique rpoBallelic type and tested for their ability to grow at 6°C and 10°C in Skim Milk Broth (SMB) and Brain Heart Infusion (BHI) broth over 21 days. Whole genome sequence data of all 28 isolates were compared phylogenetically and based on gene presence-absence.
Results: Of the 28 selected strains, all were able to grow at 6°C and 10°C in BHI broth and at 10°C in SMB; however, only 14 grew at 6°C in SMB. Isolates clearly cluster into three phylogenetic clades and four different growth patterns, which can be described as long lag phase, short lag phase, no growth, and die off. Phylogenetic clade II had higher representation of isolates with the die-off growth pattern, and was characterized by the loss of the gene glnQ, encoding for glutamine transport protein, which has been previously associated with psychrotolerance of Bacillus subtilis. Although the loss of glnQ was significantly associated with clade II, the die-off growth pattern was not.
Significance: We did not find any significant associations between growth patterns and the presence/absence of individual genes. The lack of clear gene associations ultimately complicates the development of specific detection strategies for P. odorifer group strains that can cause fluid milk spoilage.