Abstract
Lactic acid is widely used in the food, pharmaceutical, textile and chemical industries. Also, poly-lactic acid (PLA) is in increasing demand as an environmentally friendly and biodegradable plastic. In our prior study, a lactic acid-producing, xylose-fermenting Saccharomyces cerevisiae strain (SR8 LDH) has been developed. In the present study, we tested the SR8 LDH strain under various fermentation conditions to discover the most important condition determining lactic acid and ethanol production profiles. Using xylose as a substrate significantly improved lactic acid yields compared to using glucose under microaerobic conditions. High initial cell density improved lactic acid productivity, but it did not affect ethanol production. Lastly, when fermenting xylose, the PDC1 gene encoding pyruvate decarboxylase was transcriptionally repressed, which might be associated with the production of low ethanol and high lactic acid. These results indicate that the type of a carbon source, i.e. using xylose instead of glucose could be a promising solution for lactic acid production by engineered S. cerevisiae.
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