Electrical impedance studies on a culture of a newly discovered strain of Streptomyces

Electrical impedance studies were performed in the frequency range of 10 Hz-13 MHz on a culture of a newly discovered strain of Streptomyces. Data obtained in low conductivity media using concentrated bacterial suspensions in water showed the existence of two dispersions for both the conductivity and permittivity: the low-frequency alpha-dispersion, ascribed to the ions in the diffuse layer of the cellular wall and the high frequency beta-dispersion, ascribed to charging of the cytoplasmic membrane. It is in the ''low-frequency range'' of the beta-dispersion that the conductance and capacitance measurements can provide biomass-selective information. From experiments performed in the culture broth, it was found that in the audio-frequency range, the capacitance of the suspension is dominated by the polarization term, and its modification with the incubation time is indicative of the changes in the growth medium due to the metabolic process. The changes of macroscopic electrical properties of the medium capacitance (measured in the audio-frequency range) and conductance (measured in the low radio-frequency range) vs. the incubation time were found to parallel the growth curve obtained by dry weight measurements. Direct information on biomass increase during fermentation was obtained from two types of measurements in the low RF frequency: the capacitance in the low RF range and the difference between the conductance of the growth medium and that of the suspension. (C) 1997 Elsevier Science Inc.