Simple constrained-optimization view of acetate overflow in E. coli.

Area of Science:

• Microbial physiology
• Metabolic engineering
• Systems biology

Background:

• Escherichia coli (E. coli) can produce acetate as a byproduct during aerobic growth.
• Understanding the metabolic regulation of acetate production is crucial for optimizing microbial processes.

Purpose of the Study:

• To investigate the conditions under which aerobically growing E. coli produces acetate.
• To model acetate production using a flow network with the objective of maximal Adenosine Triphosphate (ATP) synthesis.

Main Methods:

• Formulation of the problem as a metabolic flow network.
• Analysis of flux constraints, including NADH turnover rate and key Krebs cycle enzyme activity.
• Comparison of model predictions with experimental data for E. coli K-12.

Main Results:

• The model predicts a switch to acetate overflow metabolism when specific flux constraints are imposed.
• Acetate overflow is predicted under limitations of NADH turnover or key Krebs cycle enzyme activity.
• The model's prediction for Krebs cycle enzyme limitation is formally equivalent to experimentally determined correlations.

Conclusions:

• Metabolic network constraints, rather than solely oxygen availability, can drive acetate production in aerobic E. coli.
• The developed flow network model accurately predicts acetate overflow under specific physiological conditions.
• This study provides a theoretical framework validated by experimental data for understanding E. coli acetate overflow.