Effects of copper on dielectric properties of E. coli cells

Dielectric properties of E. coli cells before and after Cu2+ incubation were investigated by using the dielectric spectroscopic technique. The dielectric spectra are analyzed theoretically by means of the extended three-shell ellipsoidal model, which can reflect the complicated morphological structure of E. coli cell including the outer membrane, the periplasmic space, the inner membrane and the cytoplasm. The results showed that dielectric properties of these cellular components were changed with Cu2+ treatment in a time- and concentration-dependent way. The permttivity of the outer membrane increased with the incubation time and concentration of Cu2+, possibly because polarizability of the outer leaflet of lipopolysaccharides was affected by Cu2+. The conductivity of the periplasmic space decreased with the incubation time and concentration of Cu2+, possibly due to the damage of peptidoglycan. The decreased permittivity of the inner membrane may be caused by disturbance of the lipid bilayer structure produced by Cu2+ incubation. The decreased cytoplasmic conductivity may be the consequence of the leakage of K+ from it. The cytoplasmic permittivity decreased with Cu2+ treatment probably because of the leakage of its some components. (C) 2007 Elsevier B.V. All rights reserved.