Engineered E. coli Strain for High-Yield L-Valine Fermentation
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Solution Overview
Problem
Current methods for producing L-valine using E. coli strains face challenges such as unbalanced coenzyme supply and demand, low sugar-acid conversion rates, and high production costs due to excessive pyruvate conversion into CO2 through tricarboxylic acid cyclic metabolism during aerobic fermentation.
Innovation Solution
A genetically engineered E. coli strain is developed by integrating Bacillus subtilis acetolactate synthase and ppGpp 3′-pyrophosphate hydrolase mutant genes, knocking out certain genes to alter metabolic pathways, and employing a two-stage dissolved oxygen control process to optimize L-valine production, balancing coenzyme use and improving sugar-acid conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If aerobic fermentation with exuberant respiration is used to produce L-valine, then the metabolic activity of the strain is high, but excessive pyruvate is converted into CO2 through tricarboxylic acid cyclic metabolism, resulting in low sugar-acid conversion rate and high production cost
Solution Approach 1:
The patent extracts pyruvate from the tricarboxylic acid cyclic metabolism pathway by knocking out the pdh operon (pyruvate dehydrogenase), preventing pyruvate from being converted to acetyl-CoA and subsequently lost as CO2. This redirects pyruvate flux toward L-valine synthesis, improving sugar-acid conversion rate while maintaining metabolic activity through alternative pathways.
Solution Approach 2:
The patent dynamically regulates the metabolic pathway by conditionally expressing the ilvGM operon under anaerobic conditions. This dynamic control allows the strain to maintain high metabolic activity when needed while preventing excessive pyruvate consumption through the TCA cycle, thereby improving sugar-acid conversion efficiency.
2Loss of energy
If the pdh operon is knocked out to prevent pyruvate conversion to CO2, then sugar-acid conversion rate is improved, but the strain's respiratory metabolism is compromised
Solution Approach 1:
The patent applies local quality by specifically targeting the pyruvate dehydrogenase pathway for knockout while preserving other respiratory metabolism pathways. This localized modification allows the strain to maintain overall respiratory functionality while preventing the specific loss of pyruvate to CO2, thus improving sugar-acid conversion without completely compromising respiratory metabolism.
Solution Approach 2:
The patent introduces an intermediary pathway by overexpressing the ilvGM operon, which provides an alternative route for pyruvate utilization. This intermediary pathway compensates for the lost respiratory metabolism function by channeling pyruvate toward L-valine synthesis, maintaining metabolic reliability while improving conversion efficiency.
3Productivity
If Corynebacterium glutamicum is used for L-valine production with plasmid overexpression of key enzyme genes, then L-valine metabolic flux is increased, but plasmid instability and adverse effects on bacterial cell growth occur, leading to prolonged fermentation cycle
Solution Approach 1:
The patent merges the key enzyme genes (ilvGM operon) directly into the chromosome of E. coli, eliminating the need for separate plasmid vectors. This integration ensures stable inheritance of the metabolic flux enhancement traits without plasmid instability issues, while maintaining bacterial cell growth and shortening the fermentation cycle.
Solution Approach 2:
The patent replaces the expensive and unstable plasmid system with a simpler, more stable chromosomal integration approach. This substitution eliminates the need for complex plasmid maintenance and reduces fermentation cycle time, making the process more economically viable and operationally efficient.
4Reliability
If feedback inhibition of L-valine on acetolactate synthase is not removed, then the strain maintains natural metabolic regulation, but L-valine synthesis is limited by feedback inhibition from the final product
Solution Approach 1:
The patent changes the kinetic parameters of acetolactate synthase by introducing a mutated version (ilvG) from Bacillus subtilis that is resistant to feedback inhibition by L-valine. This parameter change allows the enzyme to maintain high activity even in the presence of high L-valine concentrations, thereby increasing L-valine synthesis rate while preserving essential metabolic regulation through other mechanisms.
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 engineered strain significantly enhances L-valine titer and sugar-acid conversion rate, reducing fermentation energy consumption and byproduct accumulation, thereby lowering production costs and improving metabolic efficiency.
Implementation Method 1
method for producing L-valine by fermentation
Data Source
AI summary
A genetically engineered strain having high-yield of L-valine is disclosed. Starting from Escherichia coli W3110, an acetolactate synthase gene alsS of Bacillus subtilis is inserted into a genome thereof and overexpressed; a ppGpp 3′-pyrophosphate hydrolase mutant R290E/K292D gene spoTM of Escherichia coli is inserted into the genome and overexpressed; a lactate dehydrogenase gene ldhA, a pyruvate formate lyase I gene pflB, and genes frdA, frdB, frdC, frdD of four subunits of fumaric acid reductase are deleted from the genome; a leucine dehydrogenase gene bcd of Bacillus subtilis replaces a branched chain amino acid transaminase gene ilvE of Escherichia coli; and an acetohydroxy acid isomeroreductase mutant L67E/R68F/K75E gene ilvCM replaces the native acetohydroxy acid isomeroreductase gene ilvC of Escherichia coli. Furthermore, the L-valine fermentation method is improved by using a two-stage dissolved oxygen control. The L-valine titer and the sugar-acid conversion rate are increased.