Yeasts as Producers of Polyhydroxyalkanoates: Genetic Engineering of Saccharomyces cerevisiae

Abstract

The genes of the poly(β-hydroxybutyrate) (PHB) synthesis pathway in Ralstonia eutropha and Methylobacterium extorquens were successfully established in the yeast Saccharomyces cerevisiae. Expression of just the polyhydroxyalkanoate (PHA) synthase gene in some experiments, and all three PHB genes (i.e., the genes encoding β-ketothiolase, acetoacetyl-CoA reductase, and PHA synthase) in others, were detected in S. cerevisiae. Thus, it can be used as a “cell factory” for the production of PHB. The maximum amount of polyester accumulated was 6.7% (wt./wt.) when all three genes were expressed. The amount of polymer accumulated in the transgenic yeast harboring just the PHA synthase gene was similar (5.2%), but slightly lower, indicating the necessity of expressing all three genes for high PHB contents in the cells. For viable production of the polymer in yeasts, more needs to be learned about the metabolism of the yeast, especially about the pathways and intermediates competing with formation of the biopolymer. Another host probably needs to be chosen. Bacteria (on the top) with PHB inclusions and yeasts with storage compounds (on the bottom).