pH-Dependent Uptake of Fumaric Acid in Saccharomyces cerevisiae under Anaerobic Conditions

Abstract

Microbial production of C 4 dicarboxylic acids from renewable resources has gained renewed interest. The yeast Saccharomyces cerevisiae is known as a robust microorganism and is able to grow at low pH, which makes it a suitable candidate for biological production of organic acids. However, a successful metabolic engineering approach for overproduction of organic acids requires an incorporation of a proper exporter to increase the productivity. Moreover, low-pH fermentations, which are desirable for facilitating the downstream processing, may cause back diffusion of the undissociated acid into the cells with simultaneous active export, thereby creating an ATP-dissipating futile cycle. In this work, we have studied the uptake of fumaric acid in S. cerevisiae in carbon-limited chemostat cultures under anaerobic conditions. The effect of the presence of fumaric acid at different pH values (3 to 5) has been investigated in order to obtain more knowledge about possible uptake mechanisms. The experimental results showed that at a cultivation pH of 5.0 and an external fumaric acid concentration of approximately 0.8 mmol · liter ؊1 , the fumaric acid uptake rate was unexpectedly high and could not be explained by diffusion of the undissociated form across the plasma membrane alone. This could indicate the presence of protein-mediated import. At decreasing pH levels, the fumaric acid uptake rate was found to increase asymptotically to a maximum level. Although this observation is in accordance with proteinmediated import, the presence of a metabolic bottleneck for fumaric acid conversion under anaerobic conditions could not be excluded.

Enhanced malic acid production from glycerol with high-cell density Ustilago trichophora TZ1 cultivations

“…A further loss of energy can result from the export mechanism itself. It was reported that the most likely mechanism for export of dicarboxylic acids at low pH is an antiport with protons [ 47 ]. This would lead to additional H + ions pumped against the proton motive force, which consequently increases ATP consumption [ 48 ].…”

Regulating C4-dicarboxylate transporters for improving fumaric acid production

“…15 Employing the two dicarboxylic acid transporter genes SFC1 and SpMAE1 facilitated an improvement of fumarate production in C. glabrata. 11 However, there has been to our knowledge no report about engineering an export system to improve FA production in E. coli.…”

Advances in bio‐based production of dicarboxylic acids longer than C4

“…As one of the most important factors during fermentation, pH of the medium also significantly affects the metabolic profile [91,92]. The cell physiology could be either influenced by different concentrations of H + directly or in different forms of the chemicals depending on the pH of the environment [93,94]. The DCAs may be present in three forms namely undissociated, protonated and semi-dissociated according to the pH of the environment and the pK A values of the two carboxylic groups [95,96].…”