Identification and elimination of biosynthetic oxygen requirements in yeasts

Saccharomyces cerevisiae is a natural producer of ethanol and industrial strains can produce ethanol at high volumetric rates and near-theoretical yields. In addition to its fast fermentative metabolism, its GRAS (generally recognized as safe) status, ease of genetic engineering, tolerance to low pH and high ethanol concentrations contribute to the popularity of S. cerevisiae as an industrial platform organism. Ethanolic fermentation is, however, not unique to S. cerevisiae. Other facultatively fermentative yeast species share many performance characteristics with S. cerevisiae and may even hold additional advantages for industrial application. However, they typically lack one key distinctive phenotype of S. cerevisiae: its capability to grow fast in the absence of oxygen on simple media with minimal addition of vitamins and anaerobic growth factors. This characteristic is essential for industrial application, as aeration of large bioreactors is expensive and near-theoretical yields of fermentation products can only be achieved in the absence of respiratory dissimilation of sugars.