The Effect of Dilution Rate upon Protein Content and Cellular Amino Acid Profiles in Chemostat Cultures of Saccharomyces Cerevisiae CABI 039916

Abstract

In the present study we examined the use of a chemostat system to investigate the impact of changes in the specific growth rate of Saccharomyces cerevisiae CABI 039916 on cellular amino acid profiles and total protein content. This experimental system allowed the unambiguous examination of the link between changes in dilution rate and the culture response, which would have been difficult in batch or fed-batch cultures. Alteration of the specific growth rate (via manipulation of the dilution rate) within a carbon and energy-limited chemostat has a significant impact on the physiology of Saccharomyces cerevisiae. Low dilution rates (<0.1h-1) led to predominantly respiratory metabolism and the maximisation of cellular protein content within the cell (58%), by contrast high dilution rates (>0.2h-1) led to respirofermentative metabolism, where the cellular protein content was minimal (~40%). The content of nearly all amino acids in the yeast protein pool fell significantly as dilution rate increased in parallel with the decline in cell protein content. By contrast, the concentration of two related key food/feed amino acids in the cell protein pool—glutamic acid and arginine could be increased within the cellular protein by 5% (increasing the dilution rate from 0.05h-1 to 0.25h-1) and 1.5% respectively (decreasing the dilution rate from 0.05h-1 to 0.2h-1). Despite previous studies showing that metabolic change was associated with major changes in free amino acid levels, the present study indicates that the total cellular yeast protein amino acid composition is largely invariant despite profound metabolic changes, with one or two key exceptions.