Rewiring central metabolism in Komagataella phaffii for efficient mannose synthesis.

BACKGROUND

Mannose has wide-ranging applications but microbial fermentation remains underdeveloped compared to biotransformation for its production. The yeast Komagataella phaffii stands out as a premier synthetic biology platform, renowned for its safety profile and exceptional suitability for high-density fermentation. This established chassis organism is ideally positioned for large-scale mannose production through targeted rewiring of its mannose biosynthetic pathway via metabolic engineering.

RESULTS

K. phaffii was metabolically engineered for efficient mannose production using a dual carbon source system: glycerol for biomass generation and glucose for mannose synthesis. To redirect carbon flux toward fructose-6-phosphate (F6P) accumulation at the glycolytic node, glycolytic flux was attenuated by knocking out the phosphofructokinase II (pfk2) gene and downregulating phosphofructokinase I (pfk1). Simultaneously, pentose phosphate pathway flux was reduced by downregulating glucose-6-phosphate dehydrogenase (zwf1). To enhance mannose biosynthesis, conversion of F6P into mannose was promoted by suppressing phosphomannose isomerase (PAS_chr3_1115) and overexpressing the Escherichia coli-derived phosphatase gene yniC. Additionally, three genes involved in arabinitol and ribitol production (PAS_chr2-2_0019, PAS_chr4_0754, and PAS_chr4_0988) were deleted to suppress byproduct accumulation. The engineered strain achieved ~ 121.1 g/L mannose in high-cell-density, fed-batch fermentation, representing the highest reported titer via microbial fermentation to date.

CONCLUSIONS

This study achieved efficient mannose production in K. phaffii by remodeling central metabolism. It not only offers a new route for mannose biosynthesis but also establishes a model framework for engineering K. phaffii to produce other high-value bioactive compounds.