Modified E. coli for D-lactic acid production
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Solution Overview
Problem
Current methods for producing D-lactic acid using Escherichia coli result in low productivity and high levels of by-products such as pyruvic acid, succinic acid, and fumaric acid, which decrease the optical purity and quality of the final product, and there is a lack of efficient techniques to suppress by-product production while maintaining high D-lactic acid productivity.
Innovation Solution
A method involving the use of Escherichia coli strains with inactivated or decreased pyruvate formate-lyase (pfl) activity and enhanced NADH-dependent D-lactate dehydrogenase (ldhA) activity, combined with the inactivation of FAD-dependent D-lactate dehydrogenase (dld) and malate dehydrogenase (mdh) and aspartate ammonia-lyase (aspA) activities, to produce D-lactic acid with reduced by-products and high optical purity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If wild type Escherichia coli is used for D-lactic acid production, then the host is suitable for gene recombination and grows rapidly, but productivity for D-lactic acid is low and by-products are produced
Solution Approach 1:
The patent applies parameter changes by modifying the metabolic pathway parameters of E. coli through gene disruption. Specifically, pfl gene disruption changes the pyruvate metabolism parameter to eliminate formic acid production, and ldhA gene enhancement changes the lactate dehydrogenase activity parameter to increase D-lactic acid productivity. This resolves the contradiction by transforming the metabolic parameters rather than changing the host organism itself.
2Ease of operation
If conventional E. coli strains are used, then the host is available and easy to culture, but by-products such as pyruvic acid, succinic acid, and fumaric acid are produced in high amounts
Solution Approach 1:
The patent applies the taking out principle by removing the harmful by-product formation pathways from the E. coli metabolic system. Through disruption of pfl, mdh, and aspA genes, the patent extracts and eliminates the metabolic routes that produce formic acid, succinic acid, and fumaric acid, respectively. This allows the use of easy-to-culture E. coli while removing the harmful by-product generation.
Solution Approach 2:
The patent changes the metabolic parameters by disrupting specific genes controlling by-product formation. The pfl disruption eliminates formic acid pathway, mdh disruption eliminates succinic acid pathway, and aspA disruption eliminates fumaric acid pathway. Simultaneously, ldhA enhancement increases D-lactic acid production parameter, achieving high purity product with easy culturing.
3Manufacturing precision
If multiple gene disruptions are performed to reduce by-products, then by-product levels decrease and optical purity increases, but the complexity of the production method increases
Solution Approach 1:
The patent applies segmentation by dividing the by-product reduction strategy into separate, targeted gene disruptions. Instead of attempting a comprehensive metabolic overhaul, the patent segments the problem into three specific gene targets: pfl for formic acid, mdh for succinic acid, and aspA for fumaric acid. Each disruption is independently optimized, simplifying the overall complexity while achieving high manufacturing precision.
4Quantity of substance
If pyruvate formate-lyase activity is enhanced to increase pyruvic acid production, then substrate availability for D-lactic acid increases, but formic acid by-product increases
Solution Approach 1:
The patent applies the blessing in disguise principle by converting the harmful formic acid production pathway into a beneficial one. Instead of blocking pyruvate metabolism, the patent disrupts pfl to prevent formic acid formation while redirecting pyruvate flow through alternative pathways toward D-lactic acid production via enhanced ldhA. This transforms the potential harm of active pyruvate metabolism into a benefit for D-lactic acid synthesis.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly increases D-lactic acid productivity and optical purity, while minimizing the production of by-products like pyruvic acid, succinic acid, and fumaric acid, leading to a higher quality and more economically viable production process.
Implementation Method 1
activity of pyruvate formate-lyase (pfl) is inactivated or decreased
Implementation Method 2
enhanced NADH-dependent D-lactate dehydrogenase (ldhA) activity
Implementation Method 3
NADH-dependent D-lactate dehydrogenase (ldhA) activity
Implementation Method 4
inactivation of FAD-dependent D-lactate dehydrogenase (dld)
Implementation Method 5
inactivation of malate dehydrogenase (mdh)
Implementation Method 6
inactivation of aspartate ammonia-lyase (aspA) activities
Data Source
AI summary
A method for producing D-lactic acid in high yield, and to provide a method for producing D-lactic acid with high selectivity, in which optical purity is high and a by-product organic acid is small. In one aspect, a microorganism, wherein activity of pyruvate formate-lyase (pfl) is inactivated or decreased, and further activity of Escherichia coli-derived NADH-dependent D-lactate dehydrogenase (ldhA) is enhanced, is cultured to efficiently produce D-lactic acid. With regard to a method for enhancing ldhA activity, by linking, on a genome, a gene encoding ldhA with a promoter of a gene which controls expression of a protein involved in a glycolytic pathway, a nucleic acid biosynthesis pathway or an amino acid biosynthesis pathway, suitable results are obtained compared to the method for enhancing expression of the gene using an expression vector. A microorganism in which a dld gene is substantially inactivated or decreased is cultured to produce high quality D-lactic acid with reduced concentration of pyruvic acid.