Triacetic acid lactone production from Saccharomyces cerevisiae

Triacetic acid lactone (TAL) is a potential platform chemical produced from acetyl-CoA and malonyl-CoA by the Gerbera hybrida 2-pyrone synthase (2PS) gene.  Studies are ongoing to optimize production, purification, and chemical modification of TAL, which can be used to create the commercial chemicals hexanoic acid, γ-caprolactone, and 2,4-pentanedione.  2PS produces TAL in Saccharomyces cerevisiae; however, previous studies have resulted in low TAL yields.  In this study, 2PS was introduced into a variety of industrial and lab S. cerevisiae strains and TAL production was measured.  2PS was introduced with two different promoters, TEF and ADH2, and, while TAL production was significantly dependent on promoter, neither promoter had higher TAL production overall.  TAL was measured via HPLC from the culture supernatant, as efflux measurements have shown that TAL is actively exported.  Strains were grown with different carbon sources in batch culture, and while production varied between strains, variation between carbon sources predominated.  When grown in glucose, TAL production requires aeration, an indication that the ethanol from glucose fermentation is used to make TAL.  Feeding yeast strains ethanol as the carbon source results in higher TAL concentration, supporting this observation.    TAL production from both glycerol and acetate was low.  The highest producing strain from batch culture is now being grown with a low ethanol feed in aerated bioreactors, increasing the TAL concentration to ~ 5 g/L.  Bioreactor conditions are currently being optimized.