ever, the interpretation of the electrophoretic mobility in The conductivity of bacterial cell suspensions has been studied terms of z-potential and electrokinetic charge requires inforover a wide range of ionic strengths and is interpreted in terms mation about the mobile charge inside the bacterial wall. A of their cell wall properties. The experimental data have been full characterization of the electrical double layer of bacterial analyzed after improving the high ka double-layer theory of Fixsurfaces can therefore only be obtained from a combination man, by accounting for ionic mobility in the hydrodynamically of different experimental techniques. stagnant layer, i.e., in the bacterial wall. Static conductivity and
In a previous study (2) we have shown that the total cell dielectric dispersion measurements both show that the counterions wall charge can be determined by potentiometric proton titrain the porous gel-like cell wall give rise to a considerable surface conductance. From a comparison of the mobile charge with the tions of isolated cell wall fragments. In that study it has been total cell wall charge it is inferred that the mobilities of the ions found that the cell wall charge density (s 0 ) can be as high in the bacterial wall are of the same order but somewhat lower than as 0.5-1.0 C/m 2 , which may give rise to an appreciable those in the bulk electrolyte solution. The occurrence of surface surface conductance within the hydrodynamically stagnant conductance reduces the electrophoretic mobility in electrophorelayer. The contribution of the counterions in the bacterial sis studies. If this effect is not taken into account, the z-potential wall to the surface conductance depends on their concentrawill be underestimated, especially at low electrolyte concentrations, their mobilities and the ease by which they can migrate
tions. α§ 1997 Academic Press
into the wall at one side of the cell and leave it at the other.