Carbon dioxide fixation via production of succinic acid from glycerol in engineered Saccharomyces cerevisiae.

Background: The microbial production of succinic acid (SA) from renewable carbon sources via the reverse TCA (rTCA) pathway is a process potentially accompanied by net-fixation of carbon dioxide (CO). Among reduced carbon sources, glycerol is particularly attractive since it allows a nearly twofold higher CO-fixation yield compared to sugars. Recently, we described an engineered Saccharomyces cerevisiae strain which allowed SA production in synthetic glycerol medium with a maximum yield of 0.

Engineering for Succinic Acid Production From Glycerol and Carbon Dioxide.

Previously, our lab replaced the endogenous FAD-dependent pathway for glycerol catabolism in by the synthetic NAD-dependent dihydroxyacetone (DHA) pathway. The respective modifications allow the full exploitation of glycerol's higher reducing power (compared to sugars) for the production of the platform chemical succinic acid (SA) via a reductive, carbon dioxide fixing and redox-neutral pathway in a production host robust for organic acid production. Expression cassettes for three enzymes converting oxaloacetate to SA in the cytosol ("SA module") were integrated into the genome of -DHA, an optimized CEN.

Anaplerotic reactions active during growth of Saccharomyces cerevisiae on glycerol.

Anaplerotic reactions replenish TCA cycle intermediates during growth. In Saccharomyces cerevisiae, pyruvate carboxylase and the glyoxylate cycle have been experimentally identified to be the main anaplerotic routes during growth on glucose (C6) and ethanol (C2), respectively. The current study investigates the importance of the two isoenzymes of pyruvate carboxylase (PYC1 and PYC2) and one of the key enzymes of the glyoxylate cycle (ICL1) for growth on glycerol (C3) as a sole carbon source.

Glycerol as a substrate for Saccharomyces cerevisiae based bioprocesses - Knowledge gaps regarding the central carbon catabolism of this 'non-fermentable' carbon source.

Glycerol is an interesting alternative carbon source in industrial bioprocesses due to its higher degree of reduction per carbon atom compared to sugars. During the last few years, significant progress has been made in improving the well-known industrial platform organism Saccharomyces cerevisiae with regard to its glycerol utilization capability, particularly in synthetic medium. This provided a basis for future metabolic engineering focusing on the production of valuable chemicals from glycerol.

Towards the exploitation of glycerol's high reducing power in Saccharomyces cerevisiae-based bioprocesses.

One advantage of using glycerol as a carbon source for industrial bioprocesses is its higher degree of reduction compared to glucose. In order to exploit this reducing power for the production of reduced compounds thereby significantly increasing maximum theoretical yields, the electrons derived from glycerol oxidation must first be saved in the form of cytosolic NAD(P)H. However, the industrial platform organism Saccharomyces cerevisiae naturally uses an FAD-dependent pathway for glycerol catabolism transferring the electrons to the respiratory chain.