Project description:Identification of novel alleles conferring superior production of rose flavor phenylethyl acetate using polygenic analysis in yeast
Project description:Polygenic analysis of tolerance to carbon dioxide inhibition of isoamyl acetate “banana” flavor production in yeast reveals MDS3 as major causative gene
Project description:This research work investigates the expression of the genes involved in flavor compound production in two hybrids between Saccharomyces cerevisiae and S. kudriavzevii under low (12°C) and moderate fermentation temperatures (28°C).
Project description:Background: Anaerobic Saccharomyces cerevisiae cultures require glycerol formation to re-oxidize NADH formed in biosynthetic processes. Introduction of the Calvin-cycle enzymes phosphoribulokinase (PRK) and ribulose-1,5-biphosphate carboxylase/oxygenase (RuBisCO) has been shown to couple re-oxidation of biosynthetic NADH to ethanol production and improve ethanol yield on sugar in fast-growing batch cultures. Since growth rates in industrial ethanol-production processes are not constant, performance of engineered strains was studied in slow-growing cultures. Results: In slow-growing anaerobic chemostat cultures (D = 0.05 h-1), an engineered PRK-RuBisCO strain produced 80-fold more acetaldehyde and 30-fold more acetate than a reference strain. This observation suggested an imbalance between in vivo activities of PRK-RuBisCO and formation of NADH in biosynthesis. Lowering the copy number of the RuBisCO-encoding cbbm expression cassette from 15 to 2 reduced acetaldehyde and acetate yields by 67% and 29%, respectively. Additional C-terminal fusion of a 19 amino-acid tag to PRK reduced its protein level by 13-fold while acetaldehyde and acetate production decreased by 94% and 61%, respectively, relative to the 15x cbbm strain. These modifications did not affect glycerol production at 0.05 h-1 but caused a 4.6 fold higher glycerol production per amount of biomass in fast-growing (0.29 h-1) anaerobic batch cultures than observed for the 15x cbbm strain. In another strategy, the promoter of ANB1, whose transcript level positively correlated with growth rate, was used to control PRK synthesis in a 2x cbbm strain. At 0.05 h-1, this strategy reduced acetaldehyde and acetate production by 79% and 40%, respectively, relative to the 15x cbbm strain, without affecting glycerol yield. The maximum growth rate of the resulting strain equalled that of the reference strain, while its glycerol yield was 72% lower. Conclusions: Acetaldehyde and acetate formation by slow-growing cultures of engineered S. cerevisiae strains carrying a PRK-RuBisCO bypass of yeast glycolysis was attributed to an in vivo overcapacity of PRK and RuBisCO. Reducing the capacity of PRK and/or RuBisCO was shown to mitigate this undesirable byproduct formation. Use of a growth-rate-dependent promoter for PRK expression highlighted the potential of modulating gene expression in engineered strains to respond to growth-rate dynamics in industrial batch processes.
Project description:Extending the G1 phase improves the production of lipophilic compounds in yeast by boosting enzyme expression and increasing cell size
Project description:Optimizing the balance between heterologous acetate- and CO2-reduction pathways in anaerobic cultures of Saccharomyces cerevisiae strains engineered for low glycerol production
