Abstract
A pH-homeostatic mechanism for alkaliphilic bacteria has been proposed taking the important role of anionic polymer layer in their cell walls into account. Donnan equilibria in the bacterial cell walls were calculated to estimate the pH values inside the polymer layer of the cell walls when the outer aqueous solution is in alkaline nature. The fixed charge concentration in the polymer layer was estimated to be 2–5 mol/l from the data reported for Gram-positive bacteria, particularly for an alkaliphilic bacterium Bacillus halodurans C-125. The salt concentrations of near isotonic conditions were taken as the outer aqueous solutions. The pH values calculated for the inside of the polymer layer (the cell wall) were smaller than those of the outer solution by 1–1.5 pH units. This result agrees well with the expected values estimated from the stability of cell membranes.
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