An energetic model for oxygen-limited metabolism

Area of Science:

• Microbial biotechnology
• Metabolic engineering
• Biochemical engineering

Background:

• Microbial production of 2,3-butanediol (2,3-BDO) by Klebsiella oxytoca is influenced by oxygen availability.
• Oxygen limitation dictates substrate oxidation to 2,3-BDO and coproducts (acetic acid, acetoin, ethanol).
• Substrate flow to energetic and biosynthetic pathways is regulated by the degree of oxygen limitation.

Purpose of the Study:

• To derive energetic relationships describing microbial responses to oxygen limitation.
• To model cell mass and substrate profiles based on oxygen limitation.
• To understand the relationship between oxygen levels, growth phases, and 2,3-BDO productivity.

Main Methods:

• Derivation of two energetic relationships to describe oxygen-limited microbial metabolism.
• Modeling of cell mass and substrate dynamics using the derived relationships.
• Kinetic studies in batch and continuous cultures to observe growth phases.

Main Results:

• Two distinct growth phases were identified: energy-coupled and energy-uncoupled growth.
• Energy-coupled growth occurs below a critical oxygen limitation.
• Energy-uncoupled growth occurs at or beyond the critical oxygen limitation.

Conclusions:

• Optimal 2,3-butanediol production is achieved during the energy-coupled growth phase.
• The degree of oxygen limitation is a critical control parameter for microbial 2,3-BDO synthesis.
• The derived models provide a framework for optimizing fermentation conditions for 2,3-BDO production.