Perturbation of anion balance during inhibition of growth of Escherichia coli by weak acids - PubMed (original) (raw)
Perturbation of anion balance during inhibition of growth of Escherichia coli by weak acids
A J Roe et al. J Bacteriol. 1998 Feb.
Abstract
During inhibition of cell growth by weak acids, there is substantial accumulation of the weak acid anions in the cytoplasm. This study was undertaken to determine the impact of anion accumulation on cellular pools. At pH 6, growth in the presence of 8 mM acetate led to an internal pool of greater than 240 mM acetate anion and resulted in reduced levels of glutamate in the cell, but there were no significant changes in K+ and Na+ levels. At low osmolarity, the change in the glutamate pool compensated for only a small fraction of the accumulated acetate anion. However, at high osmolarity, glutamate compensated for over half of the accumulated acetate. Recovery of the normal cytoplasmic pH after the removal of acetate was dependent on the synthesis of glutamate.
Figures
FIG. 1
Changes in pHi and acetate pool levels upon addition of 8 mM acetate to E. coli Frag1 at pH 6. Acetate (8 mM) was added to E. coli cells growing at pH 6. (a) pHi was determined by the distribution of radioactive benzoate (□), as described in Materials and Methods. (b) Acetate pool levels (•) were determined as described in Materials and Methods. The predicted acetate pool level (◊) based upon a pK of 4.7 for acetate, the free acetate anion concentration outside the cells (7.6 mM), and the pHi determined by benzoate distribution is indicated. The data shown are composites from several independent experiments in which the time courses were overlapped to enable rapid sampling.
FIG. 2
Glutamate and acetate pool levels in E. coli cells upon treatment with acetate. Pools of acetate and glutamate were measured in parallel incubations at pHo 6, as described in Materials and Methods. Acetate (8 mM) was added at zero time. Symbols: •, glutamate; □, acetate. The data are drawn from several experiments with overlapping sample times to enable rapid kinetics determinations to be performed.
FIG. 3
Changes in growth rate, pHi, and glutamate pool levels upon suspension of acetate-treated cells in acetate-free medium. (a) Cultures were grown to exponential phase in pH 6 medium containing either acetate or benzoate. The growth data for both acetate-treated and benzoate-treated cultures obtained prior to transfer to acid-free medium are represented by a single set of data points (▵). After approximately 3 h of incubation, the cells were rapidly filtered and transferred into pH 6 medium without the weak acid, and the incubation was continued. Symbols: ▪, acetate-treated cells; •, benzoate-treated cells. (b) Cells were pregrown at pH 6 in the presence of 8 mM acetate, and the cytoplasmic pH (□) and glutamate pool levels (•) were determined as described in Materials and Methods. After a 5-min preincubation period, cells were transferred into acetate-free medium, pHo 6, and the changes in pHi and glutamate pool levels were recorded.
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