Improvement of D-lactic acid production from methanol by metabolically engineered Komagataella phaffii via ultra-violet mutagenesis

Methanol has attracted attention as an alternative carbon source to petroleum. Komagataella phaffii, a methanol-assimilating yeast, is a useful host for the chemical production from methanol. A previous study successfully constructed a metabolically engineered K. phaffii GS115/S8/Z3 strain capable of producing D-lactic acid from methanol. In this study, we aimed to develop a strain with improved D-lactic acid production by applying ultra-violet mutagenesis to the D-lactic acid-producing strain, GS115/S8/Z3. The resulting mutant strain DLac_Mut2_221 produced 5.38 g/L of D-lactic acid from methanol, a 1.52-fold increase compared to the parent strain GS115/S8/Z3. Transcriptome analysis revealed 167 differentially expressed genes in DLac_Mut2_221, comprising 104 upregulated and 63 downregulated genes. These results suggest that the improvement in D-lactic acid production from methanol in the mutant strain involves three important mechanisms: (1) avoiding excessive formaldehyde accumulation, (2) activating the glyoxylate pathway, and (3) reducing the expression of O-glycosylated proteins required for cell wall stability. Metabolic engineering strategies for K. phaffii based on the knowledge gained from this study will contribute to improving the productivity of various useful chemicals from methanol.