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Applied and Environmental Microbiology, June 2000, p. 2330-2335, Vol. 66, No. 6
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

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

Henrik Siegumfeldt,* K. Björn Rechinger, and Mogens Jakobsen

Department of Dairy and Food Science, Food Microbiology, The Royal Veterinary and Agricultural University, 1958 Frederiksberg C, Denmark

Received 15 November 1999/Accepted 8 March 2000

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.

* Corresponding author. Mailing address: Department of Dairy and Food Science, Food Microbiology, The Royal Veterinary and Agricultural University, Rolighedsvej 30, 1958 Frederiksberg C, Denmark. Phone: 45 35283286. Fax: 45 35283214. E-mail: hsi{at}kvl.dk.

Applied and Environmental Microbiology, June 2000, p. 2330-2335, Vol. 66, No. 6
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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