The effects of
nitrogen starvation on the anaerobic physiology of Saccharomyces cerevisiae were studied in cells cultivated in a
bioreactor. The composition of the
mineral medium was designed such that the
nitrogen source became depleted while there was still ample
glucose left in the medium. The culture was characterized by acoustic gas analysis, flow injection analysis and HPLC analysis of extracellular substrates and metabolites. During the cultivation, the macromolecular composition of the cells was analysed with respect to the cellular content of
RNA,
protein,
trehalose and
glycogen. During exponential growth under anaerobic conditions, the maximum specific growth rate conditions. Depletion of
ammonium in the medium led to an abrupt decrease (mumax) of S. cerevisiae CBS 8066 (0.46 h-1) was identical to the mumax determined under aerobic in the flux through glycolysis. Subsequently, a continuous decrease in the
carbon dioxide evolution rate, caused by catabolite inactivation of the
hexose-transport system, was observed. The apparent half-life of the transport system under
nitrogen starvation was 13 h. During the exponential growth phase, the cellular content of
RNA and
protein was 15% (w/w) and 60% (w/w), respectively. At the end of the cultivation where the cells had been starved of
nitrogen for 18 h, the cellular content of
RNA and
protein had decreased to 4% (w/w) and 22% (w/w), respectively. The intracellular
carbohydrate content increased dramatically as
trehalose and
glycogen accumulated to final concentrations of 7% (w/w) and 25% (w/w), respectively.
Glycerol formation during
nitrogen starvation was higher than that accounted for by the formation of organic
acids, suggesting a
protein turnover of approximately 6% h-1. The growth energetics of S. cerevisiae CBS 8066 also changed as a result of
nitrogen starvation, and YxATP was observed to increase from 80 mmol g-1 during the exponential growth phase to more than 130 mmol g-1 towards the end of the cultivation. The presented results illustrate the effect of
nitrogen starvation on glycerol formation,
protein turnover, catabolite inactivation of the
sugar-transport system, the cellular composition, the cell cycle and growth energetics.