Triacetic acid lactone production in industrial Saccharomyces yeast strains

Authors: Saunders, Lauren; Bowman, Michael; Mertens, Jeffrey; DA SILVA, NANCY - University Of California; Hector, Ronald - Ron

Submitted to: Journal of Industrial Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/29/2015
Publication Date: 2/15/2015
Publication URL: http://handle.nal.usda.gov/10113/60670
Citation: Saunders, L.P., Bowman, M.J., Mertens, J.A., Da Silva, N.A., Hector, R.E. 2015. Triacetic acid lactone production in industrial Saccharomyces yeast strains. Journal of Industrial Microbiology and Biotechnology. 42:711-721.

Interpretive Summary: Ethanol has been the product of initial focus as a renewable fuel. However, chemicals and other fuels with improved characteristics can also be made from biomass-derived sugars. The current petroleum-based approach for making these fuels and chemicals is non-sustainable. Made from biomass-derived sugars, chemical precursors could be used to manufacture a larger variety of chemicals, without relying on petroleum. Triacetic acid lactone (TAL) is a potential platform chemical that can be produced in yeast. To evaluate the potential for industrial Saccharomyces cerevisiae yeast strains to produce TAL, the enzyme required for TAL production was expressed in thirteen industrial yeast strains of varied genetic background. TAL production varied 63-fold between strains. Ethanol, acetate, and glycerol were also tested as potential carbon sources. Batch cultures with ethanol medium produced the most TAL. Therefore, cultivation with continuous ethanol feed was assayed for TAL production in bioreactors, producing our highest TAL titer, 5.2 g/L. Higher feed rates resulted in a loss of TAL and subsequent production of additional TAL side products. Finally, TAL export from the cell was measured and it was determined that TAL is actively exported from S. cerevisiae cells. Percent yield for all strains was low, indicating that further metabolic engineering of the strains is required.

Technical Abstract: Triacetic acid lactone (TAL) is a potential platform chemical that can be produced in yeast. To evaluate the potential for industrial yeast strains to produce TAL, the g2ps1 gene encoding 2-pyrone synthase was transformed into thirteen industrial yeast strains of varied genetic background. TAL production varied 63-fold between strains when compared in batch culture with glucose. Ethanol, acetate, and glycerol were also tested as potential carbon sources. Batch cultures with ethanol medium produced the highest titers. Therefore, cultivation with continuous ethanol feed was assayed for TAL production in bioreactors, producing our highest TAL titer, 5.2 g/L. Higher feed rates resulted in a loss of TAL and subsequent production of additional TAL side products. Finally, TAL efflux was measured and TAL is actively exported from S. cerevisiae cells. Percent yield for all strains was low, indicating that further metabolic engineering of the strains is required.