Monitoring changes in internal pH of Burkholderia cenocepacia in response to external pH shifts

Burkholderia cenocepacia is a Gram-negative, opportunistic pathogen that frequently causes severe infections in cystic fibrosis patients. B. cenocepacia survives in acidic environments such as compartments inside free-living amoeba and phagosomes in mammalian macrophages. Survival in acidic environments is a genus-wide property of Burkholderia species. However, very little research has been done regarding the bacterial response to low pH, including changes in the cytoplasmic pH upon exposure to low external pH (pHe). Cytoplasmic pH is an indicator of bacterial response to pHe changes. It affects many cellular processes, like enzyme function and nucleic acid stability, and needs to be carefully controlled to maintain bacterial viability. Thus, bacterial growth at different pH values is partly dependant on the ability to regulate internal pH (pHi). This project used a pH-sensitive fluorescent protein to measure the pHi of B. cenocepacia when exposed to acidic and basic pHe. At neutral pHe, the pHi of B. cenocepacia was close to neutral, similar to that of other neutralophilic bacteria such as Escherichia coli and Pseudomonas putida. In response to changes in pHe, B. cenocepacia maintained its pHi within a narrow range of 7.0-8.0. Moreover, pHi showed less fluctuations at an acidic pHe compared to a basic pHe. These results show for the first time the pHi of B. cenocepacia as well as the pHi changes it exhibits in response to changing pHe. These findings could facilitate further research into the mechanisms of pH homeostasis in B. cenocepacia, which could add to the current understanding of its pathogenesis.