Comparison of metabolic profiles of yeasts based on the difference of the Crabtree positive and negative

Abstract

The Crabtree effect involves energy management in which yeasts utilize glycolysis as the terminal electron acceptor instead of oxygen, despite the presence of sufficient dissolved oxygen, when oxygen concentrations exceed a certain limit. The Crabtree effect is detrimental to bakery yeast production, because it results in lower cellular glucose yields. Batch culture of Saccharomyces cerevisiae, a Crabtree positive yeast, decreased the cell yield of glucose and produced large amounts of ethanol despite a high specific glucose consumption rate compared to Candida utilis, a Crabtree negative yeast. This study investigated the effect of these characteristics on metabolite levels. We performed metabolome analysis of both yeasts during each growth phase of batch culture using liquid chromatography-tandem mass spectrometry and gas chromatography-mass spectrometry. Principle component analysis of metabolome data indicated that the Crabtree effect affected metabolites related to NADH synthesis in central metabolism. The amount of these metabolites in S.cerevisiae was lower than that in C.utilis. However, to maintain the specific glucose consumption rate at high levels, yeasts must avoid depletion of NAD+, which is essential for glucose utilization. Our results indicated that NADH was oxidized by converting acetaldehyde to ethanol in S.cerevisiae, which is in accordance with previous reports. Therefore, the specific NADH production rates of S.cerevisiae and C.utilis did not show a difference. This study suggested that NAD+/NADH ratio is disrupted by the Crabtree effect, which in turn influenced central metabolism and that S.cerevisiae maintained the NAD+/NADH ratio by producing ethanol.