Open AccessDynamic Changes of Intracellular pH in Individual Lactic Acid Bacterium Cells in Response to a Rapid Drop in Extracellular pH
Author(s) -
Henrik Siegumfeldt,
K. Björn Rechinger,
Mogens Jakobsen
Publication year - 2000
Publication title -
applied and environmental microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.552
H-Index - 324
eISSN - 1070-6291
pISSN - 0099-2240
DOI - 10.1128/aem.66.6.2330-2335.2000
Subject(s) - streptococcus thermophilus , lactic acid , lactococcus lactis , bacteria , intracellular ph , lactobacillus , extracellular , chemistry , biochemistry , population , microbiology and biotechnology , biology , fermentation , genetics , demography , sociology
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 ofLactobacillus delbrueckii subsp.bulgaricus ,Streptococcus thermophilus , andLactococcus 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 ofL. 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 ofS. thermophilus .