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EFFECT OF pH AND AMMONIUM IONS ON THE PERMEABILITY OF BACILLUS PASTEURII

Department of Bacteriology and Public Health, Washington State University, Pullman, Washington

ABSTRACT

WILEY, W. R. (Washington State University, Pullman), AND J. L. STOKES. Effect of pH and ammonium ions on the permeability of Bacillus pasteurii. J. Bacteriol. 86:1152–1156. 1963.—Cell suspensions of Bacillus pasteurii require an alkaline pH (8.5 to 9.0) and NH₄⁺ for the oxidation of low concentrations (4 µM) of fumaric acid, glutamic acid, alanine, and other oxidizable substrates. In contrast, cells disrupted by a French press or by lysozyme oxidize these substrates at pH 7.2 and without NH₄⁺. Moreover, the alkaline pH and NH₄⁺ inhibit substrate oxidation by the broken cells. These striking differences between whole and disrupted cells suggest that pH and NH₄⁺ affect whole cells externally and not internally. It appears that the alkaline pH is needed to convert NH₄⁺ to free NH₃. The latter in turn is required by the cells for the transport of low concentrations of substrate across the cell membrane. At high concentrations (20 to 250 µM), substrates force entry into the cells by simple diffusion, thereby eliminating the need for a high pH and NH₄⁺ for oxidation.