[Toxic effect of hydroxylated ions of heavy metals on the cytoplasmic membrane of bacterial cells].

The influence of nickel, copper, cadmium, and lead ions at concentrations of 50 to 100 microM on the barrier properties of the plasma membrane (PM) and the electrophoretic mobility (EPM) of Pseudomonas fluorescens 71, Escherichia coli K-12, and Mycobacterium phlei B-1291 VKM cells was studied at pH values from 5 to 9 by electro-orientational (EO) spectroscopy and microelectrophoresis of cells. According to the data of EO spectroscopy, the increase in the toxicity of heavy metal cations to cells corresponded to transition of cations to monovalent hydroxylated forms. Hydroxylated ions were found to more easily adsorb on, or penetrate across, the PM and to bind to competent proteins. During the treatment of all three investigated microorganisms with Cu and Pb ions, and gram-negative bacteria also with Ni ions, the EPM of cells changed in a pH range corresponding to the transition of bivalent metal ions to their monovalent hydroxylated forms. Changes in the EPM induced by increasing pH correlated well with the enhanced toxicity of these metals to the PM, as evidenced by the EO spectroscopy data. At the same time, this correlation was less pronounced for cadmium sulfate toxicity to all of the microorganisms studied and for nickel chloride toxicity to M. phlei cells.