Recombinant E. coli Strain for Succinic Acid Production
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Solution Overview
Problem
Current methods for producing succinic acid through fermentation with E. coli strains face low production efficiency due to by-product accumulation, unbalanced cofactor metabolism, and inability to tolerate high substrate concentrations, leading to low yields and space time yields.
Innovation Solution
A recombinant E. coli strain is developed by knocking out genes encoding pyruvate formate lyase, lactate dehydrogenase, and phosphotransacetylase, and overexpressing phosphoenolpyruvate carboxykinase and phosphite dehydrogenase using Red homologous recombination and expression vectors like pTrcHisA, facilitating balanced metabolism and increased succinic acid production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If traditional E. coli fermentation is used for succinic acid production, then the process is simple and E. coli is easy to operate, but the production efficiency is low with significant by-product accumulation
Solution Approach 1:
The patent applies parameter changes by systematically modifying multiple genetic parameters simultaneously - knocking out four genes (pflB, ldhA, pta, ackA) and overexpressing three genes (ppsA, pck, sdhA) to optimize metabolic flux. This multi-parameter optimization transforms E. coli from a low-efficiency succinic acid producer to a high-yield strain achieving 1.43 g/L/h space-time yield
Solution Approach 2:
The patent extracts and eliminates harmful by-product formation pathways by knocking out specific genes responsible for producing lactic acid (ldhA), formic acid (pflB), and acetic acid (pta and ackA). This extraction of harmful metabolic routes redirects carbon flux toward succinic acid, reducing by-product accumulation while maintaining ease of operation
2Productivity
If glucose concentration is increased to improve production rate, then the space time yield increases, but the strain cannot tolerate high substrate concentrations causing metabolic imbalance
Solution Approach 1:
The patent applies preliminary action by pre-engineering the strain's metabolic capacity before high-glucose fermentation. The knockout of ackA and pta genes, combined with overexpression of ppsA, prepares the metabolic pathway to handle high glucose loads by preventing acetic acid accumulation and enhancing oxaloacetate supply, thereby enabling the strain to tolerate and efficiently utilize high substrate concentrations
Solution Approach 2:
The patent implements dynamics by creating a flexible metabolic network that can adapt to varying glucose concentrations. The combination of gene knockouts and overexpressions creates a dynamic system where carbon flux automatically redirects toward succinic acid production when glucose is abundant, maintaining metabolic balance across different substrate concentrations
3Manufacturing precision
If by-product formation pathways are eliminated to improve succinic acid purity, then the yield increases, but the metabolic balance becomes unbalanced
Solution Approach 1:
The patent merges multiple metabolic optimization strategies into a unified system - combining gene knockouts (pflB, ldhA, pta, ackA) with gene overexpressions (ppsA, pck, sdhA) to simultaneously achieve high succinic acid purity and metabolic balance. The coordinated modification of these genes creates synergistic effects where carbon flux is redirected to succinic acid while NADH balance and anaplerotic pathways are maintained
Solution Approach 2:
The patent applies parameter changes by systematically adjusting multiple metabolic parameters - enzyme activities, gene expression levels, and pathway fluxes - to achieve both high purity and metabolic stability. The overexpression of ppsA increases oxaloacetate supply, pck enhancement improves phosphoenolpyruvate carboxykinase activity, and sdhA overexpression boosts succinate dehydrogenase function, collectively maintaining metabolic balance while eliminating by-products
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
The recombinant strain achieves a succinic acid production of 137 g/L with a yield of 1 g/g glucose and a space time yield of 1.43 g/L/h, with minimal by-product formation, particularly reducing lactic acid, formic acid, and acetic acid accumulation.
Implementation Method 1
using renewable resources to fix carbon dioxide
Implementation Method 2
phosphite dehydrogenase ptxD involved in the succinate synthesis pathway
Implementation Method 3
Red homologous recombination technology
Data Source
AI summary
The invention provides a recombinant Escherichia coli strain for producing succinic acid and a construction method thereof. The by-product encoding genes in the E. coli strain FMME-N-2 are knocked out to obtain the E. coli strain FMME-N-5 (ΔfocA-pflB-ΔldhA-Δpta-ackA); and the phosphoenolpyruvate carboxykinase pck derived from Actinobacillus succinogenes and the phosphite dehydrogenase ptxD derived from Pseudomonas stutzeri were overexpressed. The constructed plasmid pTrcHisA-pck-ptxD was introduced into the expression host E. coli FMME-N-5 (ΔfocA-pflB-ΔldhA-Δpta-ackA), and the cells were screened in a plate containing ampicillin, to obtain an engineered strain E. coli FMME-N-5 (ΔfocA-pflB-ΔldhA-Δpta-ackA)-pck-ptxD that can efficiently produce succinic acid. After fermentation by a two-stage fermentation strategy, the production of succinic acid reaches 137 g/L, the yield of succinic acid is up to 1 g/g glucose, and the space time yield is 1.43 g/L/h, while no by-products of lactic acid and formic acid are accumulated, and the acetic acid content is 1-2 g/L.