CONDUCTIVITY AND DIELECTRIC-DISPERSION OF GRAM-POSITIVE BACTERIAL-CELLS

The conductivity of bacterial cell suspensions has been studied over a wide range of ionic strengths and is interpreted in terms of their ce ll wall properties. The experimental data have been analyzed after imp roving the high kappa alpha double-layer theory of Fixman, by accounti ng for ionic mobility in the hydrodynamically stagnant layer, i.e., in the bacterial wall. Static conductivity and dielectric dispersion mea surements both show that the counterions in the porous gel-like cell w all give rise to a considerable surface conductance. From a comparison of the mobile charge with the total cell wall charge it is inferred t hat the mobilities of the ions in the bacterial wall are of the same o rder but somewhat lower than those in the bulk electrolyte solution. T he occurrence of surface conductance reduces the electrophoretic mobil ity in electrophoresis studies. If this effect is not taken into accou nt, the zeta-potential will be underestimated, especially at low elect rolyte concentrations. (C) 1997 Academic Press