The effect of dissolved oxygen concentration on the growth physiology of Saccharomyces cerevisiae whi2 mutants.

Isogenic whi2 and WHI2+ strains of Saccharomyces cerevisiae were grown in a 2-litre bioreactor as batch cultures on a medium containing yeast extract and peptone with either glucose or ethanol as carbon and energy source. The concentration of dissolved oxygen within the medium was varied over the range of 0 to 100% saturation. Expression of the whi2 phenotype only occurred above 40% oxygen saturation with either glucose or ethanol as carbon and energy source. Under these conditions the whi2 cells could be distinguished from WHI2+ cells in that they were phase dark, highly budded and very small during the stationary growth phase, and reached final cell densities four to six times higher than WHI2+ cells. The results clearly show that the WHI2 gene of S. cerevisiae plays an important role in cell proliferation and that the availability of oxygen, or some product of oxidative metabolism, is involved in regulating the phenotypic expression of mutations within this gene.