Low‐pH production of d‐lactic acid using newly isolated acid tolerant yeast Pichia kudriavzevii NG7

Lactic acid is a platform chemical for the sustainable production of various materials. To develop a robust yeast platform for low‐pH production of d‐lactic acid (LA), an acid‐tolerant yeast strain was isolated from grape skins and named Pichia kudriavzevii NG7 by ribosomal RNA sequencing. This strain could grow at pH 2.0 and 50°C. For the commercial application of P. kudriavzevii NG7 as a lactic acid producer, the ethanol fermentation pathway was redirected to lactic acid by replacing the pyruvate decarboxylase 1 gene (PDC1) with the d‐lactate dehydrogenase gene (d‐LDH) derived from Lactobacillus plantarum. To enhance lactic acid tolerance, this engineered strain was adapted to high lactic acid concentrations, and a new transcriptional regulator, PAR1, responsible for acid tolerance, was identified by whole‐genome resequencing. The final engineered strain produced 135 g/L and 154 g/L of d‐LA with productivity over 3.66 g/L/hr at pH 3.6 and 4.16 g/L/hr at pH 4.7, respectively. To construct a low‐pH d‐lactic acid (LA) production system, the extreme acid‐tolerant P. kudriavzevii NG7 strain was isolated, engineered to produce d‐LA, and adapted to high concentrations of d‐LA. This strain produced 135 g/L of D‐LA with productivity 3.66 g/L/hr at a low pH condition. A new transcriptional regulator, PAR1, responsible for P. kudriavzevii acid tolerance was identified.