[Nature of lactate secretion by E. coli cells]

The fluxes of H+, K+ and Lac-- ions in suspension of E. coli were studied by means of ion-selective electrodes. It was shown that the stoichiometry of DCCD-sensitive ionic exchange is 2H : K+ : Lac--. It was supposed that the bacteria maintains intracellular macroscopic electroneutrality by secretion of Lac-- anions during activity of proton-potassium pump, which exchange 2H+ from the cell for one extracellular K+-ion.