Oxygen, pH value, and carbon source induced changes of the mode of oscillation in synchronous continuous culture of Saccharomyces cerevisiae

Oscillations of measured process parameters occur in continuous cultures of Saccharomyces cerevisiae owing to a partial synchronization of budding. In tentional changes of the oxygen concentration, pH value, and carbon source cause effects on the period length similar to those known from variations o f the dilution rate. The generation times of parent and daughter cells freq uently differ in synchronous culture. To analyze the oscillation the term m ode IJ of oscillation is used, which is defined as the ratio IJ of the gene ration times of parent and daughter cells. When the dissolved oxygen concen tration was reduced to zero, the mode of oscillation changed within two per iods from mode 12 to mode 11, caused by a decrease of the generation time o f daughter cells and an increase of that of the parent cells. When the pH v alue was slowly reduced from 5.0 to 3.9, a change from mode 112 to mode 13 was observed. Mode 13, representing one parent and three daughter cell popu lations (the start of budding of each of the three being delayed by one per iod), denotes an elongated generation time of the daughter cells compared t o mode 112, marked by one parent and two different daughter cell classes. W hen the carbon source galactose was replaced by glucose a mode change from mode 12 to mode 11 was observed. This alteration of the mode was found to b e dependent on the status of the cell cycle at the time when the carbon sou rce is changed. The population distribution in batch cultures with glucose or galactose as a substrate was analysed by dyeing the DNA and counting the bud scars. Galactose provoked higher growth rates for the older cells, Acc ording to the model for stationary synchronous growth parameters like DO, p H value or the type of carbon source can be varied within a certain range w ithout effecting the period length. If the variation imposes a certain stre ss, the culture switches to a new mode. These kinds of parameters therefore provide selective measures to influence the period lengths and the modes o f oscillation. (C) 1999 John Wiley & Sons, Inc.