Genetically engineered yeast platform for efficient low-pH bioproduction of citramalate and related chemicals

Background

The production of methyl methacrylate (MMA), a crucial monomer for polymethyl methacrylate (PMMA or acrylic glass), has traditionally relied on petrochemical processes such as the acetone cyanohydrin (ACH) route. These methods involve hazardous reagents, generate significant toxic waste, and contribute to greenhouse gas emissions, raising environmental and safety concerns. As industries seek more sustainable and eco-friendly alternatives, attention has shifted toward biotechnological approaches that use renewable resources to produce MMA precursors, such as citramalate. Citramalate can be biologically synthesized and chemically converted to methacrylic acid and MMA, offering a promising route to greener PMMA production. However, the feasibility of this approach depends on the ability to efficiently produce citramalate at industrial scales, ideally under conditions that minimize downstream processing costs and environmental impact.

Current microbial production methods for citramalate face several limitations. Most conventional microbes, such as Escherichia coli or Saccharomyces cerevisiae, are not naturally tolerant to the low-pH conditions that would simplify citramalate recovery and reduce the need for costly neutralization and reacidification steps. As a result, fermentation processes often require pH control with added chemicals, increasing operational complexity, cost, and waste generation. Additionally, genetic engineering tools for non-conventional, acid-tolerant yeasts are underdeveloped, making it difficult to optimize these organisms for high-yield citramalate production. The lack of robust, stable expression systems and efficient metabolic flux redirection in these hosts further hampers the scalability and economic viability of biobased citramalate production, leaving a significant gap in the development of sustainable MMA manufacturing processes.

Technology

This technology centers on a genetically engineered strain of the acid-tolerant yeast Issatchenkia orientalis designed for efficient production of citramalate, a valuable precursor for methacrylic acid and methyl methacrylate (MMA). The yeast is modified to express a heterologous, codon-optimized citramalate synthase (CimA) gene, which is stably integrated into the genome using a piggyBac transposon system. By knocking out or downregulating the endogenous pyruvate decarboxylase (PDC) gene, the metabolic pathway is redirected from ethanol production toward citramalate synthesis. The engineered yeast can ferment in low-pH media, leveraging its natural acid tolerance to simplify downstream citramalate recovery and reduce the need for costly neutralization and reacidification steps. This system utilizes advanced genetic tools, including codon optimization and multi-copy genome integration, to ensure high and stable production yields.

The differentiation of this technology lies in its holistic integration of metabolic engineering, genetic optimization, and process innovation. Unlike conventional microbial production systems that require neutral pH and extensive downstream processing, this approach exploits the unique acid tolerance of I. orientalis to enable direct low-pH fermentation, significantly cutting operational costs and environmental impact. The use of the piggyBac transposon system for stable, multi-copy gene integration ensures consistent, high-level expression of the citramalate pathway, outperforming traditional plasmid-based systems. Additionally, the modularity of the platform allows for further metabolic enhancements and adaptation to other non-conventional yeasts, offering a versatile and scalable solution for sustainable citramalate and MMA production from renewable resources.

Benefits

• Enables efficient citramalate production at low pH, eliminating costly and environmentally harmful neutralization and acidification steps.
• Uses genetically engineered Issatchenkia orientalis yeast with stable, multi-copy genome integration of citramalate synthase for consistent high-level production.
• Redirects metabolic flux from ethanol to citramalate by knocking out or downregulating pyruvate decarboxylase, improving yield.
• Leverages the natural acid tolerance of the yeast to maintain viability and productivity under industrial fermentation conditions.
• Reduces process costs and carbon footprint by up to 30% compared to conventional petrochemical MMA production methods.
• Provides a versatile platform adaptable to other non-conventional yeasts and further metabolic engineering for enhanced production.
• Facilitates sustainable bioproduction of MMA precursors from renewable resources, supporting greener industrial and medical applications.

Applications

• Biobased MMA monomer production
• Eco-friendly PMMA (acrylic glass) manufacturing
• Low-pH industrial organic acid fermentation

Additional info

Engineered *Issatchenkia orientalis* strains express heterologous, codon-optimized citramalate synthase (CimA) via piggyBac transposon-mediated genomic integration. Deleting endogenous pyruvate decarboxylase redirects metabolic flux from ethanol toward citramalate synthesis. This acid-tolerant platform enables high-titer fermentation in low-pH media, streamlining product recovery. The resulting bio-based citramalate serves as a precursor for methacrylic acid and methyl methacrylate, providing a sustainable alternative to petrochemical-based acrylic glass manufacturing.