Metabolic engineering ofSaccharomyces cerevisiae for production of carboxylic acids: current status and challenges

Abstract

To meet the demands of future generations for chemicals and energy and to reduce the environmental footprint of the chemical industry, alternatives for petrochemistry are required. Microbial conversion of renewable feedstocks has a huge potential for cleaner, sustainable industrial production of fuels and chemicals. Microbial production of organic acids is a promising approach for production of chemical building blocks that can replace their petrochemically derived equivalents. Although Saccharomyces cerevisiae does not naturally produce organic acids in large quantities, its robustness, pH tolerance, simple nutrient requirements and long history as an industrial workhorse make it an excellent candidate biocatalyst for such processes. Genetic engineering, along with evolution and selection, has been successfully used to divert carbon from ethanol, the natural endproduct of S. cerevisiae, to pyruvate. Further engineering, which included expression of heterologous enzymes and transporters, yielded strains capable of producing lactate and malate from pyruvate. Besides these metabolic engineering strategies, this review discusses the impact of transport and energetics as well as the tolerance towards these organic acids. In addition to recent progress in engineering S. cerevisiae for organic acid production, the key limitations and challenges are discussed in the context of sustainable industrial production of organic acids from renewable feedstocks.

Key Process Conditions for Production of C 4 Dicarboxylic Acids in Bioreactor Batch Cultures of an Engineered Saccharomyces cerevisiae Strain

“…Equilibrium ratios were calculated on the assumption that all three compounds are exported via monoanion proton symport, on a proton motive force across the yeast plasma membrane of Ϫ150 mV and an intracellular pH of 7 and on the following acid dissociation (pK a ) constants: malate, 3.46 and 5.10; pyruvate, 2.39; succinate, 4.16 and 5.61. Calculations were performed as described earlier (1,43 Not only does the culture pH impact the thermodynamics of product export, but also it has been reported that a low extracellular pH, combined with the presence of organic acids, can decrease the cytosolic pH (11,28). With a pK a of 6.35, the equilibrium between carbon dioxide and bicarbonate would be strongly influenced by changes in the intracellular pH.…”

Engineering furfural tolerance in Escherichia coli improves the fermentation of lignocellulosic sugars into renewable chemicals

“…Escherichia coli and yeasts have proven to be excellent biocatalysts for metabolic engineering (11,12). However, both are inhibited by furan aldehydes (7,8,(13)(14)(15) and both contain NADPH-dependent oxidoreductases that convert furfural and hydroxymethylfurfural (dehydration product of hexose sugars) into less toxic alcohols (15)(16)(17).…”

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

“…Additional advantages of this organism are that its genome has been fully sequenced and that it is considered by the American Food and Drug Administration (FDA) as an organism generally regarded as safe (GRAS) (6). In addition, in several recent studies, the yeast S. cerevisiae has been proposed as a cell factory for the production of bulk chemicals, such as malic, lactic, and citric acid from renewable substrates (1,30,36,42,43).…”