Glucosamine Yield Improvement in Engineered Saccharomyces cerevisiae with Ethanol Yield Reduction by Carbon Flux...

Glucosamine (GlcN) is an essential amino monosaccharide widely used in pharmaceuticals, nutraceuticals, and cosmetics. Microbial fermentation presents a sustainable alternative to its traditional chemical production. However, in Saccharomyces cerevisiae, competitive carbon flux towards ethanol significantly limits GlcN yields. In this study, an S. cerevisiae strain for GlcN biosynthesis was engineered by integrating heterologous GlmD (glucosamine-6-phosphate deaminase) and GlmP (glucosamine-6-phosphate phosphatase) genes. To redirect carbon flux, the pyruvate decarboxylase genes pdc1, pdc5, and pdc6 were sequentially knocked out using the Clustered Regularly Interspaced Short Palindromic Repeats Cas9 (CRISPR-Cas9) approach, generating strains S. cerevisiaeGlmDP/pdc1Δ, GlmDP/pdc1Δpdc5Δ, and GlmDP/pdc1Δpdc5Δpdc6Δ. S. cerevisiae GlmDP/pdc1Δpdc5Δpdc6Δ achieved a GlcN titer of 2.20 ± 0.11 g/L, a 1.54-fold increase over the parental S. cerevisia GlmDP strain, while its ethanol yield decreased by 26%. This enhancement was achieved without significantly affecting cell growth or glucose consumption. Comparative transcriptomics between the triple-knockout and parental yeasts revealed 892 differentially expressed genes. Pathways related to glycolysis and ethanol formation were predominantly downregulated, whereas pathways potentially supporting GlcN synthesis were upregulated. The engineered strain demonstrated high genetic stability over 50 generations. Our findings demonstrate that disrupting ethanol formation is an effective strategy to enhance GlcN production in S. cerevisiae, providing valuable insights for carbon flux redistribution.