Low-frequency dielectric dispersion of bacterial cell suspensions.
Dielectric spectra of Escherichia coli cells suspended in 0.1-10 mM NaCl were measured over a frequency range of 10 Hz to 10 MHz. Low-frequency dielectric dispersion, so-called the α-dispersion, was found below 10 kHz in addition to the β-dispersion, due to interfacial polarization, appearing above 100 kHz. When the cells were killed by heating at 60°C for 30 min, the β-dispersion disappeared completely, whereas the α-dispersion was little influenced. This suggests that the plasma (or inner) membranes of the dead cells are no longer the permeability barrier to small ions, and that the α-dispersion is not related to the membrane potential due to selective membrane permeability of ions. The intensity of the α-dispersion depended on both of the pH and ionic strength of the external medium, supporting the model that the α-dispersion results from the deformation of the ion clouds formed outside and inside the cell wall containing charged residues.
Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan. Electronic address: asami@e.kuicr.kyoto-u.ac.jp.
Koji
K
Asami
D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D002463:Cell Membrane Permeability; D058266:Dielectric Spectroscopy; D004058:Diffusion; D004553:Electric Conductivity; D004926:Escherichia coli / Q000187:drug effects / Q000502:physiology*; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D050296:Microbial Viability; D009994:Osmolar Concentration; D012965:Sodium Chloride / Q000494:pharmacology; D013535:Suspensions
D013535:Suspensions; D012965:Sodium Chloride
Bacteria; Cell death; Cell wall; Counterion polarization; Dielectric dispersion; Membrane potential