Physiological responses of Crabtree positive and Crabtree negative yeasts to glucose upshifts in a chemostat

Growth and metabolic differences between a Crabtree positive yeast, Saccharomyces cerevisiae, and a Crabtree negative yeast, Kluyveromyces marxianus, were investigated using chemostat cultures under glucose limitation. When subjected to glucose upshifts ("pulses" or sudden increases in glucose availability), several physiological differences between these two yeasts became apparent. Whilst the production Of ethanol was very rapid in S. cerevisiae, there was a complete lack of alcoholic fermentation in K. marxianus. Glucose utilisation kinetics also differed, with S. cerevisiae rapidly consuming 50% of the additional available glucose (through fermentation) whilst K. marxianus was only utilised 10% of the glucose (through respiration). These and other differences suggest possible evolutionary advantages of the Crabtree effect in the metabolism of sugar rich environments by certain yeasts.