(576e) New Strategies to Eliminate Ethanol Byproduct Formation in Yeast to Enhance the Anaerobic Production of Fuels and Chemicals

The long record of the yeast Saccharomyces cerevisiae as a favored industrial organism is a testament to its robustness, low nutritional requirements, high tolerance to low pH, suitability for large-scale fermentation, and ease of genetic manipulation. However, yeast relies on ethanol production to generate energy from fermentation. Therefore, any metabolic pathway engineered in yeast for the anaerobic production of fuels or chemicals will face ethanol formation as a major competing pathway. This competition will consume most of the sugars from feedstocks to make ethanol as an undesirable side product. This central challenge of yeast metabolic engineering has been partially addressed by reducing the activities of decarboxylases or dehydrogenases involved in ethanol formation, leading to significant reduction of ethanol production. If such activities are completely eliminated cells stop producing ethanol, but they also stop growing on glucose, a preferred industrial feedstock. Restoration of growth on glucose in these strains has been achieved through directed evolution, but the evolved strains have impaired fitness and are difficult to work with. We have developed new methods to eliminate ethanol byproduct formation in yeast that overcome the limitations of current strategies. Our strains can be engineered to produce different fuels or chemicals of interest without ethanol production, thus significantly enhancing glucose utilization towards the formation of desired products.