A mathematical model for the aerobic growth of Saccharomyces cerevisiae with a saturated respiratory capacity

Abstract

SummaryA mathematical model for the aerobic growth of Saccharomyces cere\iyiae in both batch and continuous culture is described. It was based on the experimental observation that the respiratory capacity of this organism may become saturated and exhibit a maximum specific oxygen uptake rate after suitable adaptation. This experimental observation led to the possibility that transport into and out of the mitochondrion was of major importance in the overall metabolism of S. cerevisiae and was subject to long-term adaptation. Consistent with this observation a distributed model was proposed which, as its basis, assumed the control of respiration and fermentation to be the result of saturation of respiration without any specific repression or inhibition of the uptake rates of other substrates. No other regulation of fermentation and respiration was assumed. The model provided a suitable structure allowing precise quantification of the changes in rate and stoichiometry of energy production. The model clearly indicated that growth under the wide range of experimental conditions reported could not be predicted using constant values for the maximum specific respiratory rate or constant values of Y A T~ (g biomass/mol ATP) and PO ratio of (mol ATP/ atom oxygen). The causes of the variation in the respiratory rate were not determined and it was concluded that a more detailed analysis (reported subsequently) was required. The variation of Y A T~ and PO ratio with specific growth rate implied that the efficiency of ATP generation or ATP utilization decreased with increasing specific growth rate. It was concluded that it was not possible to quantify the individual effect of YATP and PO ratio until independent means for their reliable estimation is available.

Energetics of Saccharomyces Cerevisiae in Anaerobic Glucose-Limited Chemostat Cultures

“…This results in values for the P/Oratio of approximately 1-8 (e.g. Barford & Hall, 1981 ;Andrews, 1989). However, if a value of 16 is used, with a cell yield of 0.5 g cells (g glucose)-' (Postma et al, 1989), the 'effective' P/O-ratio becomes approximately 1.0.…”

In vivo investigations of glucose transport in Saccharomyces cerevisiae

“…If the Monod equation really mirrors the glucose uptake as a rate-limiting step for the growing cell then the half-saturating constant, Ks, should be equal to the value of KT in Eq. (2). Assuming that the two mobilities are the same (a = p), it then follows from Eq.…”

Direct uptake of sucrose by Saccharomyces cerevisiae in batch and continuous culture.

“…200 g) (2,5). The treatment of the culture and the time allowed for adaptation prior to the study may have a significant effect on the mechanism of transport.…”