Dielectric analysis of yeast cell growth

On-line dielectric measurements of yeast cells (Saccharomyces cerevisiae) growing in suspension culture were made over a frequency range from 0.1 to 100 MHz. The amplitude of the dielectric dispersion centered at about 1 MHz increased exponentially with cultivation time in the logarithmic growth phase and then remained constant in the stationary phase. This result clearly indicates that the mass and concentration of the yeasts can be monitored by the dielectric method. In the late logarithmic growth phase, a subdispersion appeared around 10 MHz, whose amplitude was less than 6% of that of the whole dispersion. The development of the subdispersion indicates the increase in the volume of the vacuole in the yeasts. In synchronized cell culture, the amplitude of the dispersion changed stepwise. The time interval between the steps was about 100 min. that corresponds to the generation time of the yeast.