Kinetics of growth and ethanol production on different carbon substrates using genetically engineered xylose-fermenting yeast

Saccharomyces cerevisiae 424A (LNH-ST) strain was used for fermentation of glucose and xylose. Growth kinetics and ethanol productivity were calculated for batch fermentation on media containing different combinations of glucose and xylose to give a final sugar concentration of 20 ± 0.8 g/L. Growth rates obtained in pure xylose-based medium were less than those for media containing pure glucose and glucose–xylose mixtures. A maximum specific growth rate μmax of 0.291 h−1 was obtained in YPD medium containing 20 g/L glucose as compared to 0.206 h−1 in YPX medium containing 20 g/L xylose. In media containing combinations of glucose and xylose, glucose was exhausted first followed by xylose. Ethanol production on pure xylose entered log phase during the 12–24 h period as compared to the 4–10 h for pure glucose based medium using 2% inoculum. When glucose was added to fermentation flasks which had been initiated on a pure xylose-based medium, the rate of xylose usage was reduced indicating cosubstrate inhibition of xylose consumption by glucose.