HigBA toxin-antitoxin system of Weissella cibaria is involved in response to the bile salt stress

BACKGROUND

Toxin-antitoxin (TA) systems are prevalent adaptive genetic elements in bacterial genomes, which can respond to environmental stress. While, few studies have addressed TA systems in probiotics and their roles in the adaptation to gastrointestinal transit (GIT) environments.

RESULTS

The Weissella cibaria 018 could survive in pH 3.0-5.0 and 0.5-3.0 g L^-1 bile salt, and its HigBA system responded to the bile salt stress, but not to acid stress. The toxin protein HigB and its cognate antitoxin protein HigA had 85.1% and 100% similarity with those of Lactobacillus plantarum, respectively, and they formed the stable tetramer HigB-(HigA)₂ -HigB structure in W. cibaria 018. When exposed to 1.5-3.0 g L^-1 bile salt, the transcriptions of higB and higA were up-regulated with 4.39-19.29 and 5.94-30.91 folds, respectively. Meanwhile, W. cibaria 018 gathered into a mass with 48.07% survival rate and its persister cells were found to increase 8.21% under 3.0 g L^-1 bile salt.

CONCLUSION

The HigBA TA system of W. cibaria 018 responded to the bile salt stress, but not to acid stress, which might offer novel perspectives to understand the tolerant mechanism of probiotics to GIT environment. © 2022 Society of Chemical Industry.

Stability assessment and improvement of a Lactobacillus plantarum mutant with low post-fermentation acidification characteristics

Intracellular pH homeostasis through the extrusion of a proton by F₀F₁-ATPase is one of the key mechanisms used by lactic acid bacteria in response to acid stress, and also influences their post-fermentation acidification. In this study, the genotypic and phenotypic stability of a low post-fermentation acidification (LPA) mutant (designated as DGCC12411^m) of Lactobacillus plantarum DGCC12411 was assessed. Compared with its mother strain, the pH of DGCC12411^m in De Man, Rogosa, and Sharpe (MRS) broth after 48-h cultivation was 0.35 pH units higher. Incorporation of DGCC12411^m in yogurt stored at ambient temperature (ambient yogurt) showed a reduced post-fermentation acidification during storage at 25°C for 120 d. Whole-genome sequencing analysis showed a SNP mutation (GGT > GAT at positions 505 to 507) in DGCC12411^m, which resulted in the substitution of a highly conserved glycine residue by aspartic acid at the Walker A motif of the F₀F₁-ATPase α-subunit. However, degeneration of the LPA phenotype was observed after 5 passages of DGCC12411^m in MRS broth. Analysis of DNA sequencing on both the whole population and the isolates showed that a back mutation occurred at the SNP site (GAT changed back to GGT) over the passaging, and the reversion gradually increased from a ratio of 10.8% at P5 to 60.0% at P10. We also found that the LPA phenotype stability of DGCC12411^m was improved by supplementing 0.1 M potassium phosphate buffer to the growth medium as well as by reducing the inoculation rate of DGCC12411^m to 2% (vol/vol). Such LPA Lactobacillus strains have potential for use as starter cultures in fermented foods with less change in acidity during shelf-life storage.