Physiological comparison of cells with high and low alcohol dehydrogenase activities in bacterial populations consuming ethanol

Abstract

Measuring the physiological heterogeneity of natural and industrial microbial populations is essential to studying, modelling and monitoring of microbial populations. It was discovered that populations of Escherichia coli and Bacillus megaterium growing in medium with ethanol as an external source of energy have two actively respiring but physiologically different subpopulations. Cells of one subpopulation have negligibly low alcohol dehydrogenase (ADH) activity (ADH-L cells) and cells of the other have high ADH activity (ADH-H cells). The subpopulation of ADH-H bacterial cells was measured using 10 min incubations of cells in a 1% solution of allyl alcohol for fast selective killing of cells with high activity of ADH and flow cytometry detection of dead cells after this incubation. The content of ADH-H cells during exponential phase of batch culture varied from 9 % to 90 % and lowered to zero for a few hours during starvation of the population. ADH-L cells are actively respiring cells and not depolarized cells. The simultaneous presence of ADH-L and ADH-H cells growing in the medium with ethanol can be explained by the fact that ADH-H cells oxidize actively external ethanol whereas ADH-L cells oxidize only intracellular storage carbohydrates. The method for enumeration of cells with high ADH activity can be used to monitor the heterogeneity of bacterial populations consuming ethanol as a sole source of carbon and energy.