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Homolactate fermentation by metabolically engineered Escherichia coli strains
1Center for Molecular BioEngineering, Department of Biological and Agricultural Engineering, University of Georgia, Athens, GA 30602, USA.
Applied and Environmental Microbiology
|November 24, 2006
Summary
This study engineered Escherichia coli for high-yield lactate production. Optimized strains achieved 138 g/L lactate with high efficiency, minimizing byproduct formation for industrial applications.
Area of Science:
- Biotechnology
- Metabolic Engineering
- Microbial Fermentation
Background:
- Lactate production is crucial for various industries.
- Escherichia coli engineering offers a platform for efficient biochemical synthesis.
- Optimizing fermentation pathways is key to maximizing product yield and purity.
Purpose of the Study:
- To develop a high-yield, homofermentative lactate production process in engineered Escherichia coli.
- To investigate and minimize succinate byproduct formation during fermentation.
- To enhance lactate yield, purity, and productivity through genetic modification and process optimization.
Main Methods:
- Genetic modification of Escherichia coli strains by knocking out key metabolic genes (aceEF, pfl, poxB, pps, frdABCD).
- Two-phase fermentation: aerobic growth followed by anaerobic non-growth production.
- Optimization of pH control using calcium hydroxide (Ca(OH)2).
- (13)C nuclear magnetic resonance analysis to trace metabolic pathways and byproduct formation.
Main Results:
- Engineered strain YYC202 achieved 90 g/L lactate with high yield and productivity.
- Strain ALS974 (YYC202 frdABCD) reduced succinate accumulation by 70% and achieved 138 g/L lactate.
- Optimized conditions with ALS974 yielded 0.99 g/g lactate with 97% carbon product purity and 6.3 g/L/h productivity.
- (13)C NMR confirmed succinate derived from acetate, not the glyoxylate cycle.
Conclusions:
- Homofermentative lactate production in engineered E. coli is feasible at high titers.
- Minimizing succinate formation through gene knockout (frdABCD) and acetate control significantly improves lactate yield and purity.
- This optimized process demonstrates a promising strategy for industrial-scale lactate manufacturing.
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