Engineering of Saccharomyces cerevisiae for enhanced production of L-lactic acid by co-expression of acid-stable glycolytic enzymes from Picrophilus torridus

Abstract

L-lactic acid, as a monomer of polylactic acid, has attracted much attention because of the growing market for biodegradable bioplastics to reduce landfill waste. As an industrial L-lactic acid producer, Saccharomyces cerevisiae is generally used because it survives in low pH. However, in S. cerevisiae, production of L-lactic acid causes a decrease in intracellular pH, which leads to slow glycolytic flux, and consequently results in a lower productivity of L-lactic acid. For this reason, yeast strains that maintain their growth and the activities of metabolic enzymes during lactic acid production need to be developed for industrial applications. Herein, acid stable enzymes from acidophilic archaea Picrophilus torridus were expressed in L-lactic acid producing S. cerevisiae to increase glycolytic flux at low intracellular pH conditions for a higher L-lactic acid titer. Enzymes of lower glycolysis including phosphoglycerate kinase, phosphoglycerate mutase, enolase, and pyruvate kinase from P. torridus were introduced to develop a novel L-lactic acid producing strain. It was clearly shown that the production of lactic acid in the developed strain increased by 20% compared to the parental strain. To the best of our knowledge, this is the first report of P. torridus enzymes used in metabolic engineering to enhance the metabolic flux at a lower intracellular pH. Moreover, it is expected that the new strain will have an enhanced glycolytic flux at a low pH expressing acid stable enzymes that could be used to produce other valuable organic acids with increased titers.