Impact of the relative supply of glucose and oxygen on yeast kinetic activity

• Main Author: McDonnell, J. L.
• Published: Swansea University 1999
• Subjects: 572.492
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638154

The objective of this project was to investigate the effects of the relative supplies of oxygen and glucose on the kinetic activity of the yeast <I>Saccharomyces cerevisiae</I> NCYC 1026. This study was initiated from observing yeast cells immobilised in the silicone rubber matrix material, <I>immobaSil</I> which has the property of high solubility of oxygen, reported to be eight times that of oxygen in water. Hence, would exposure of the yeast, as free cells, during storage to relatively higher or lower supplies of oxygen to glucose, lead to detrimental and irreversible changes in the kinetic activity of the yeast cells? By identifying the effects of storage conditions on yeast kinetic activity, suggestions could made as to how best to store yeast cell lines so as to promote desired levels of kinetic activity, i.e. to engineer the yeast cells to respond manner in industrial bioreaction applications, and to be able to predict the performance of immobilized cells. The yeast cells were stored as several different lines (Master Lines) which were exposed to varying supplies of oxygen and glucose during storage. Using aseptic handling techniques, these Master Lines were kept successfully for up to 1000 days continuous storage. From time to time, samples of yeast from these Master Lines were taken to produce an inoculum for free cell aerobic batch culture experiments, (Batch Runs), carried in a Stirred Tank Fermenter (STF). These batch culture experiments were conducted mainly under the initial conditions of 1000 mg/l glucose in a chemically defined liquid medium, an aeration rate of 41/min, (1 vvm), a temperature of 25<SUP>o</SUP>C and pH 4.5. The variations in the relative supplies of glucose and oxygen to yeast cells during storage time did appear to promote changes in kinetic activity, both detrimental and advantageous to industrial applications, which are identified in this study. The conclusions and observations made on this research have direct relevance to industrial applications and the development of predictable kinetic activity of yeast cells.