Fed-batch system for cultivating genetically engineered yeast that produces lactic acid via the fermentative promoter

A simple fed-batch system for cultivating genetically engineered yeast generating lactate under the regulation of the PDC1 promoter was established. Traditional strategies that avoid occurrence of Crabtree effect, such as respiratory quotient (RQ) control or ethanol control, are not applicable to the strain because of reduced generation of ethanol and CO(2) by-products. In this system, the feed rate increased when the pH was >5.0, and decreased when the pH was <5.0. Using this system, cell yields on sucrose increased by approximately 30% compared to that with the conventional RQ control method, due to the early detection of occurrence of Crabtree effect by pH decrease.