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Appl. Environ. Microbiol., Jan 1996, 178-183, Vol 62, No. 1
P Breeuwer, J Drocourt, FM Rombouts and T Abee
A novel method based on the intracellular conjugation of the fluorescent
probe 5 (and 6-)-carboxyfluorescein succinimidyl ester (cFSE) was developed
to determine the intracellular pH of bacteria. cFSE can be taken up by
bacteria in the form of its diacetate ester, 5 (and 6-)-carboxyfluorescein
diacetate succinimidyl ester, which is subsequently hydrolyzed by esterases
to cFSE in the cytoplasm. When Lactococcus lactis cells were permeabilized
with ethanol, a significant proportion of cFSE was retained in the cells,
which indicated that cFSE was bound intracellularly. Unbound probe could be
conveniently extruded by a short incubation of the cells in the presence of
a fermentable sugar, most likely by exploiting an active transport system.
Such a transport system for cFSE was identified in L. lactis, Listeria
innocua, and Bacillus subtilis. The intracellular pH in bacteria can be
determined from the ratio of the fluorescence signal at the pH-sensitive
wavelength (490 nm) and the fluorescence signal at the pH-insensitive
wavelength (440 nm). This cFSE ratio method significantly reduced problems
due to the efflux of fluorescent probe from the cells during the
measurement. Moreover, the method described was successfully used to
determine the intracellular pH in bacteria under stress conditions, such as
elevated temperatures and the presence of detergents.
Copyright © 1996, American Society for Microbiology
A Novel Method for Continuous Determination of the Intracellular pH in Bacteria with the Internally Conjugated Fluorescent Probe 5 (and 6-)-Carboxyfluorescein Succinimidyl Ester
Department of Food Science, Wageningen Agricultural University, 6703 HD Wageningen, The Netherlands, and Chemunex S.A., 94700 Maisons-Alfort, France
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