(491c) Nutritional Value Improvement of Corn Ethanol Co-Product By Yeast Engineering

With the common use of corn ethanol as a transportation fuel additive in the United States, the major co-product Distillers Dried Grains with Solubles (DDGS) is massively produced and reached 36 million metric tons in 2016. The high energy, mid-protein, and high digestible phosphorus content of DDGS make it a very attractive, partial replacement for some of the more expensive, traditional energy (corn), protein (soybean meal), and phosphorus (mono-or dicalcium phosphate) used in animal feeds. However, variability in amino acids content and digestibility has been observed and remains a challenge when DDGS is included in animal diets. Excessive nitrogen will be excreted if more crude protein is included to meet the animal requirement for amino acids. Thus, when formulating diets with DDGS, some key amino acids is often incorporated as supplement. The key amino acids that is lacking here are lysine, tryptophan and arginine. Lysine is the first limiting amino acids. Tryptophan and arginine are too costly for external addition. The present study is focused on improving nutritional value of co-products in corn ethanol biorefinery by increasing the level of the key amino acids. This was accomplished by genetic engineering of Saccharomyces cerevisiae to accumulate more key amino acids in the cell biomass, thereby increasing its level in the final co-products. Our previous results on lysine engineering showed that the free lysine content could be increased by nearly 4 time-fold in engineered strains compared with wild-type strain. The lysine in the biomass increased by around 1 time in the engineered strains. The possibility of ethanol fermentation could not be significantly affected by modifying lysine synthesis pathway was also confirmed. The engineering work on arginine and tryptophan is being in process. The polypeptides rich in arginine and tryptophan is expressed in yeast and it is expected the yeast biomass with higher ratio of arginine and tryptophan could be obtained. The better nutritionally balanced co-products would minimize the cost associated with nutrient utilization and decrease the discharge of nitrogen to the environment, which will benefit corn ethanol biorefinery, animal feed industry as well as ecosystem.