Dynamic Changes of Intracellular pH in Individual Lactic Acid Bacterium Cells in Response to a Rapid Drop in Extracellular pH

AUTOR(ES)

Siegumfeldt, Henrik

FONTE

American Society for Microbiology

RESUMO

We describe the dynamics of changes in the intracellular pH (pHi) values of a number of lactic acid bacteria in response to a rapid drop in the extracellular pH (pHex). Strains of Lactobacillus delbrueckii subsp. bulgaricus, Streptococcus thermophilus, and Lactococcus lactis were investigated. Listeria innocua, a gram-positive, non-lactic acid bacterium, was included for comparison. The method which we used was based on fluorescence ratio imaging of single cells, and it was therefore possible to describe variations in pHi within a population. The bacteria were immobilized on a membrane filter, placed in a closed perfusion chamber, and analyzed during a rapid decrease in the pHex from 7.0 to 5.0. Under these conditions, the pHi of L. innocua remained neutral (between 7 and 8). In contrast, the pHi values of all of the strains of lactic acid bacteria investigated decreased to approximately 5.5 as the pHex was decreased. No pronounced differences were observed between cells of the same strain harvested from the exponential and stationary phases. Small differences between species were observed with regard to the initial pHi at pHex 7.0, while different kinetics of pHi regulation were observed in different species and also in different strains of S. thermophilus.

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