Genetic engineering of candida utilis yeast for efficient production of L-lactic acid

Abstract

Polylactic acid is receiving increasing attention as a renewable alternative for conventional petroleum-based plastics. In the present study, we constructed a meta-bolically-engineered Candida utilis strain that produces L-lactic acid with the highest efficiency yet reported in yeasts. Initially, the gene encoding pyruvate decarbox-ylase (CuPDCl) was identified, followed by four CuPDCl disruption events in order to obtain a null mutant that produced little ethanol (a by-product of L-lactic acid). Two copies of the L-lactate dehydrogenase (l-LDH) gene derived from Bos taurus under the control of the CuPDCl promoter were then integrated into the genome of the CuPdcl -null deletant. The resulting strain produced 103.3 g/1 of L-lactic acid from 108.7 g/1 of glucose in 33 h, representing a 95.1% conversion. The maximum production rate of L-lactic acid was 4.9 g/l/h. The optical purity of the L-lactic acid was found to be more than 99.9% e.e.