BACTERIAL PERMEABILITY: THE UPTAKE AND OXIDATION OF CITRATE BY ESCHERICHIA COLI

Abstract

A direct measurement of total uptake was applied to determine whether surface impermeability could explain why extracts of Escherichia coli can oxidize exogenous citrate but intact cells cannot. The equations for the "space" method are derived and its limitations are pointed out. The observed uptake of citrate was characterized as a variable that was dependent on temperature, pH, external citrate concentration, the species and concentration of cations, and integrity of the cell, but was independent of added energy source, time, and adaptational or mutational processes. Uptake into the citrate space appeared to be a diffusional process. It was concluded that citrate normally diffuses into the cell wall, and under certain environmental conditions may penetrate further into the cell. The lack of correlation between uptake and oxidation of citrate negated the hypothesis of surface impermeability of E. coli to citrate.