In industrial settings, engineered yeasts are often used in fermentation to convert sugars into valuable products. Yeast biomass is one of the main by-products, but its value as a commodity is low. One way to maximize the value of yeast biomass is to co-produce high-value animal feed ingredients such as carotenoids.
Recently, Christopher J. Paddon et al. from Amyris, Inc. published an article in ACS Synthetic Biology 'Coproduction of Phase-Separated Carotenoids and β-Farnesene as a Yeast Biomass Valorization Strategy', the authors further modified a high β-farnesene-producing strain of Saccharomyces cerevisiae to produce two valuable products in a single fermentation, β-farnesene, which is present in the liquid phase, and the carotenoid carotenoid keratine, which is present in the cell.
The production of high levels of carotenoids in β-farnesene-producing strains negatively affected both strain growth and β-farnesene production. So the authors established a carotenoid pathway gene promoter library and screened for strains with the highest β-carotene production and minimally reduced β-farnesene production, based on which the authors screened for an efficient β-carotene ketolase that converts β-carotene to keratine.
This ultimately enabled brewer's yeast to produce both keratine (2.25 g/kg DCW) and β-farnesene (>100 g/L), and both were present in different phases without interfering with each other's purity.
