Improvement of D‐lactic acid production at low pH through expressing acid‐resistant gene IoGAS1 in engineered Saccharomyces cerevisiae

다국어 초록 (Multilingual Abstract)

Blending d‐lactic acid (d‐LA) with l‐lactic acid can significantly improve the thermostability of polylactic (PLA). Although microbial production of d‐LA under acidic conditions is beneficial for the reduction of production costs, the yield is low due to the acidic toxicity of the source strains. Herein, an Issatchenkia orientalis glycosylphosphatidylinositol‐anchored protein IoGas1, which is required for resistance to low pH and salt stress, was expressed in the YIP‐J‐C‐D‐A1 yeast strain. This strain was integrated with Escherichia coli d‐lactate dehydrogenase gene and several attenuated key pathway genes, including pyruvate decarboxylases (PDC1, PDC6), JEN1 (a monocarboxylate transporter), d‐lactate dehydrogenase1 (DLD1), l‐lactate cytochrome‐c oxidoreductase (CYB2) and alcohol dehydrogenase 1(ADH1).
The results revealed that the production of d‐LA by the modified strain YIP‐I‐J‐C‐D‐A1 was remarkably improved and reached 85.3 g L–1 d‐LA, with a yield of 0.71 g g–1 and a productivity of 1.20 g L h–1 in batch‐fed fermentation. The d‐LA production of the YIP‐I‐J‐C‐D‐A1 strain (CGMCC2.5785) was further improved by attenuating the ethanol and glycerol pathways. The resulting strain YIP‐A15G12 (CGMCC2.5803) produced 92.0 g L–1 d‐LA with a yield of 0.70 g g–1 and a productivity of 1.21 g L h–1 in batch‐fed fermentation at a final pH of 3.58.
Taken together, the expression of the acid‐resistant gene IoGAS1 in a modified yeast strain can significantly improve the efficiency of producing d‐LA at low pH, which may prove beneficial for the industrial production of the biodegradable material, PLA.