d-Lactic acid production by metabolically engineered Saccharomyces cerevisiae

Poly d-lactic acid is an important polymer because it improves the thermostability of poly l-lactic acid by the stereo complex formation. We constructed a metabolically engineered Saccharomyces cerevisiae that produces d-lactic acid efficiently. In this recombinant, the coding region of pyruvate decarboxylase 1 (PDC1) was completely deleted, and two copies of the d-lactate dehydrogenase (d-LDH) gene from Leuconostoc mesenteroides subsp. mesenteroides strain NBRC3426 were introduced into the genome. The d-lactate production reached 61.5 g/l, the amount of glucose being transformed into d-lactic acid being 61.2% under neutralizing conditions. Additionally, the yield of free d-lactic acid was also shown to be 53.0% under non-neutralizing conditions. It was confirmed that d-lactic acid of extremely high optical purity of 99.9% or higher. Our finding obtained the possibility of a new approach for pure d-lactic acid production without a neutralizing process compared with other techniques involving lactic acid bacteria and transgenic Escherichia coli.