Engineering of central carbon metabolism in recombinant Saccharomyces cerevisiae for improved production of biopolymers

Sammanfattning: Bioplastics are a promising alternative for petroleum-based plastics that today is on high demand in our contemporary lifestyles. They are made from biopolymers such as polyhydroxyalkanoates (PHAs). Producing biopolymers from waste material feedstock using microbes increases profitability and environmental benefits as well as sustainability for biorefineries. Saccharomyces cerevisiae is a robust microorganism that fits for this task. Engineered S. cerevisiae strains are already able to consume sugars present in the waste streams such as glucose and xylose, additionally also able to produce the biopolymer Poly-(R)-3-hydroxybutyrate (PHB) were in this study further engineered to improve yields, productivities and titers. In strategy one a heterologous acetylating acetaldehyde dehydrogenase (eutE) originally from Escherichia coli, was codon optimized and introduced into S. cerevisisae. In strategy two, an acetyl-CoA synthase originally from Salmonella enterica (acsL461P) was also introduced in combination with upregulated homogenous acetaldehyde dehydrogenase (ALD6). As last engineering step, to further direct the carbon flux towards PHB, alcohol dehydrogenase 1 (ADH1) was disrupted. The results show that Δadh1 strains will direct the carbon flux best towards PHB compared to the other strains. Strains expressing eutE decreased all of their PHB production suggesting that the kinetics of the heterologous acetylating acetaldehyde dehydrogenase might not be favorable for the conditions present when using xylose as a carbon source.