Impact of high hydrostatic pressure on the single nucleotide polymorphism of stress-related dnaK, hrcA, and ctsR in the Lactobacillus strains

Abstract

Lactic acid bacteria (LAB) are widespread in environments and can either have a positive impact because their ability to survive in harsh conditions and influence the product (probiotic properties, change of structure-EPS [exopolysaccharides], etc.), or a negative impact, (so not needed) because of their spoilage ability (beer, juices). High hydrostatic pressure (HHP), one of the non-thermal preservation methods used in the food industry, can force the LAB to activate the adaptative mechanisms. Under pressurization, the changes in the bacteria cells can occur at the transcriptional or translational level. This study evaluated the HHP on the single nucleotide polymorphism (SNP) changes in three genes, dnaK, ctsR, and hrcA, related to the stress-response mechanism in LAB. The correlation between the DNA polymorphism and the gene expression under HHP stress was assessed. The applied pressure of 300 MPa resulted in a low ratio of nonsynonymous substitutions to the synonymous substitutions (0 to 1.12), and a lower number of mutations was observed for pressurized strains (from 6 in hrcA to 11 in dnaK) than in controlled (from 3 in ctsR to 92 in hrcA). In all pressurized strains, the expression of genes was observed, whereas, in control strains, the gene expression was detected in three out of five strains. Although there was a noticeable change in stress-related gene expression after HHP, there was no correlation with SNPs. At the same time, with a high frequency of synonymous changes in nucleotide and high diversity for hrcA and dnaK, a very low diversity was found in ctsR sequences. The LAB strains stress response mechanisms are much more complex. The study requires information on the general mechanism and changes in the membranes’ composition, proteome changes, and gene expression patterns. The mutations in genes related to stress can have important implications for the strains’ fitness effect and adaptive ability of LAB strains, especially considering their food industry implication where the HHP techniques are used.