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Amplifying the cellular reduction potential of Streptococcus zooepidemicus
Barrie Fong Chong1, Lars K Nielsen
1Department of Chemical Engineering, The University of Queensland, Brisbane Qld 4072, Australia.
Journal of Biotechnology
|November 5, 2002
Summary
Overexpressing NADH oxidase in Streptococcus zooepidemicus boosts energy yield, shifting fermentation from lactic acid to acetate. This enhances biomass production but reveals pyruvate dehydrogenase as a key metabolic bottleneck at high expression levels.
Area of Science:
- Microbial biotechnology
- Metabolic engineering
- Biochemical engineering
Background:
- Hyaluronic acid is a valuable pharmaceutical polymer produced by Streptococcus zooepidemicus.
- Hyaluronic acid synthesis imposes a significant energetic burden on the bacteria.
- Optimizing energy metabolism is crucial for efficient bacterial fermentation.
Purpose of the Study:
- To enhance energy yield in Streptococcus zooepidemicus by overexpressing the NADH oxidase gene.
- To investigate the impact of increased NADH oxidase activity on bacterial fermentation products and biomass yield.
- To identify metabolic bottlenecks limiting acetate production at high NADH oxidase expression levels.
Main Methods:
- Cloning and overexpression of the native NADH oxidase gene in Streptococcus zooepidemicus.
- Aerobic cultivation of engineered bacteria on glucose.
- Analysis of fermentation products (lactic acid, ethanol, acetate) and biomass yield.
- Evaluation of acetate flux control coefficients at varying NADH oxidase expression levels.
Main Results:
- Overexpression of NADH oxidase increased energy yield and shifted fermentation towards acetate production.
- Lactic acid and ethanol production decreased, while acetate became the primary fermentation product.
- Biomass yield increased due to enhanced energy from acetate formation.
- High NADH oxidase levels led to pyruvate excretion, indicating a limitation in the pyruvate dehydrogenase complex.
Conclusions:
- NADH oxidase overexpression is an effective strategy to redirect bacterial metabolism towards acetate production and increase biomass yield.
- The pyruvate dehydrogenase complex represents a critical metabolic bottleneck at high NADH oxidase expression levels, limiting further acetate production.
- Metabolic engineering of NADH oxidase offers a promising approach for optimizing hyaluronic acid production by improving bacterial energy efficiency.