Dielectric properties of E. coli cell as simulated by the three-shell spheroidal model Original Research Article

Dielectric properties of E. coli cell have been re-studied by means of the three-shell spheroidal model, where the three shells correspond to the outer membrane, the periplasmic space and the inner membrane, respectively. With the model, a curve-fitting procedure has been developed to analyze the dielectric spectra. Although E. coli cell has been studied before, its special morphological structure was taken into account more comprehensively than any previous model in the present work. Dielectric properties of various cell components have been estimated from the observed dielectric spectra, especially the permittivity of the outer membrane, which was evaluated quantitatively for the first time. The values of εom were 12 for κom of 0 to 10− 4 S/m and 34 for κom of 10− 3 S/m. The specific capacitance of the inner membrane was 0.6–0.70 μF/cm2. The relative permittivity and the conductivity of the cytoplasm were about 100 and 0.22 S/m, respectively, and the conductivity of the periplasmic space was 2.2–3.2 S/m.