Enliven: Microbes and Microbial Techniques

This paper describes the physiological dualism of yeast cells during their exponential growth and the method to detect and measure the subpopulations in such alternative physiological states of cell as exotrophy or endotrophy, which are the consumptions of either extracellular or intracellular, previously accumulated sources of energy, respectively. All cells of Saccharomyces cerevisiae population growing in the medium with glucose had low alcoholdehydrogenase (ADH) activity. Meanwhile, the population growing in the medium with ethanol as a source of energy contained cells with either high ADH activity (ADH-H cells) or low ADH activity (ADH-L cells). Physiological heterogeneity of yeast cells by activity of alcoholdehydrogenase was studied using selective killing of cells with high ADH activity after 10 min incubation of cells in 1% (v/v) solution of allyl alcohol. The content of ADH-H cells increased from zero in the lag-phase to 32% in the exponential phase of batch culture and then dropped to zero in the stationary phase. Presence of both ADH-H and ADH-L cells in the yeast population growing in the medium with ethanol was explained that ADH-H cells actively oxidize external ethanol but ADH-L cells oxidize intracellular storage of carbohydrates without involvement of ADH. The method for enumeration of exotrophic and endotrophic cells can be used to monitor the heterogeneity of yeast populations consuming ethanol as a source of energy.