Oscillatory changes in the growth rate were observed in undisturbed continuous culture of Saccharomyces cerevisiae on sugar-cane molasses media when nitrogen sources (2.56 to 6.17 g/liter of ammonium sulfate or 1.22 g/liter of urea) were added to the feeding mash and when the air rate was 1.3 to 1.6 v/v/m. The oscillations were not affected by the addition of yeast extract. The suppression of the nitrogen source during the continous test leads to a nonoscillatory transient state. No oscillations occured at all when no nitrogen source was added to the medium and/or the air rate was equal to zero or equal to about 3.3 v/v/m. The oscillatory responses of the system were affected by a previous anaerobic continuous cultivation of the yeast.

SummaryThe authors studied the influence of periodic variations (one cycle per 24 hr) of the feeding mash concentration of a continuous anaerobic culture of Saccharomyces cerevisiae in sugarcane molasses media a t constant dilution rate. I t was observed that the average yield coefficients during the transient state were practically equal to the yield coefficient obtained during steady-state experiments. It was also observed, in each experiment, that the average specific growth rate during the transient state was equal to the dilution rate.

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