PROTEINS INDUCED IN ESCHERICHIA-COLI BY BENZOIC-ACID

Proteins induced by benzoic acid in Escherichia coli were observed on two-dimensional electrophoretic gels (2-D gels). Cultures were grown i n glucose-rich medium in the presence or absence of 20 mM benzoate at an external pH of 6.5, where the pH gradient (Delta pH) is large and b enzoate accumulates, and at an external pH of 8.0, where Delta pH is i nverted and little benzoate is taken up. Radiolabeled proteins were se parated on 2-D gels and were identified on the basis of the index of V anBogelen and Neidhardt. In the absence of benzoic acid, little differ ence was seen between pH 6.5 and pH 8.0; this confirms that the mechan isms of protein homeostasis in this range are constitutive, including the transition between positive and inverted Delta pH. Addition of ben zoate at pH 6.5 Increased the expression of 33 proteins. Twelve of the benzoate-induced proteins were induced at pH 8.0 as well, and nine of these matched proteins induced by the uncoupler dinitrophenol. Eighte en proteins were induced by benzoate only at pH 6.5, not at pH 8.0, an d were not induced by dinitrophenol. One may be the iron and pH regula tor Fur, which regulates acid tolerance in Salmonella spp. The other 1 3 proteins had not been identified previously. The proteins induced by benzoate only at a low pH may reflect responses to internal acidifica tion or to accumulation of benzoate.