Intracellular pH response to weak acid stress in individual vegetative Bacillus subtilis cells
Faculty of Pharmaceutical, Biomedical and Veterinary Sciences . Biomedical Sciences
Engineering sciences. Technology
Applied and environmental microbiology. - Baltimore, Md
, p. 6463-6471
University of Antwerp
The intracellular pH (pHi) critically affects bacterial cell physiology. Hence, a variety of food preservation strategies aim at perturbing pHi homeostasis. Unfortunately, accurate pHi quantification with existing methods is suboptimal since measurements average across populations of cells, not taking into account inter-individual heterogeneity. Yet, physiological heterogeneity in isogenic populations is well known to be responsible for differences in growth and division kinetics of cells in response to external stressors. To assess in this context the behavior of intracellular acidity, we have developed a robust method to quantify pHi at single-cell levels in Bacillus subtilis. Bacilli spoil food, cause disease and are well known for their ability to form highly stress-resistant spores. Using an improved version of the genetically encoded ratiometric pHluorin (IpHluorin), we have quantified pHi in individual B. subtilis cells, cultured at an external pH of 6.4, in the absence or presence of weak acid stresses. In the presence of 3 mM potassium sorbate, a decrease in pHi and an increase in the generation time of growing cells were observed. Similar, effects were observed when cells were stressed with 25 mM potassium acetate. Time-resolved analysis of individual bacteria in growing colonies shows that after a transient pH decrease, long-term pH evolution is highly cell-dependent. The heterogeneity at single cell level shows the existence of subpopulations that might be more resistant and contribute to population survival. Our approach contributes to an understanding of pHi regulation in individual bacteria and may help scrutinizing effects of existing and novel food preservation strategies.