Passive electrical properties of microorganisms. 3. Conductivity of isolated bacterial cell walls.

The dielectric properties of isolated Micrococcus lysodeikticus cell walls have been studied to establish more firmly the view that wall-associated ions play a major role in the conduction of low frequency electric current by intact bacterial cells. The conductivity of isolated walls was found to be about 0.40 mho/m. If counterions associated with fixed, ionized groups in the wall have average mobilities equal to that of sodium ions in free solution, the fixed charge concentration required to account for the measured conductivity is between 75 and 95 meq/liter of wet wall volume. Estimates of the numbers of titratable amino and carboxyl groups in wall polymers indicate that conductivity is more closely related to net wall charge than to total wall charge. The measured wall conductivity was used to predict a value of 0.15 +/- 0.03 mho/m for whole cell conductivity. This prediction is close to the measured value of 0.25 +/- 0.05 mho/m and it is thought that much of the disparity in values is related to changes in wall structure and composition during the isolation procedures.