Comparative proteome analysis of Saccharomyces cerevisiae grown in chemostat cultures limited for glucose or ethanol.

The use of chemostat culturing enables investigation of steady-state physiological characteristics and adaptations to nutrient-limited growth, while all other relevant growth conditions are kept constant. We examined and compared the proteomic response of wild-type Saccharomyces cerevisiae CEN.PK113-7D to growth in aerobic chemostat cultures limited for carbon sources being either glucose or ethanol. To obtain a global overview of changes in the proteome, we performed triplicate analyses using two-dimensional gel electrophoresis and identified proteins of interest using MS. Relative quantities of about 400 proteins were obtained and analyzed statistically to determine which protein steady-state expression levels changed significantly under glucose- or ethanol-limited conditions. Interestingly, only enzymes involved in central carbon metabolism showed a significant change in steady-state expression, whereas expression was only detected in one of both carbon source-limiting conditions for 15 of these enzymes. Side effects that were previously reported for batch cultivation conditions, such as responses to continuous variation of specific growth rate, to carbon-catabolite repression, and to accumulation of toxic substrates, were not observed. Moreover, by comparing our proteome data with corresponding mRNA data, we were able to unravel which processes in the central carbon metabolism were regulated at the level of the proteome, and which processes at the level of transcriptome. Importantly, we show here that the combined approach of chemostat cultivation and comprehensive proteome analysis allowed us to study the primary effect of single limiting conditions on the yeast proteome.