Development of linear irreversible thermodynamic model for oxidation reduction potential in environmental microbial...

Area of Science:

• Biogeochemistry
• Microbial Ecology
• Non-equilibrium Thermodynamics

Background:

• The Nernst equation, traditionally used for reversible systems, is often applied to biological oxidation-reduction potential (ORP) under irreversible, nonequilibrium conditions with significant assumptions.
• These assumptions can lead to inaccuracies in quantifying ORP in dynamic biological environments, necessitating a more appropriate model.

Purpose of the Study:

• To develop a linear nonequilibrium thermodynamic model for interpreting ORP in biological processes.
• To relate ORP to the affinities of catabolism and anabolism within biological systems.
• To establish a framework for understanding energy expenditure in biological redox reactions.

Main Methods:

• Proposed the Microbial Related Reduction and Oxidation Reaction (MIRROR) model (Model No. 1).
• Formulated ORP based on linear nonequilibrium thermodynamics.
• Related metabolic affinities (catabolism and anabolism) to ORP.

Main Results:

• The MIRROR model establishes a direct relationship between ORP and the affinities of catabolism and anabolism.
• Energy expenditure in catabolism and anabolism is shown to be proportional to overpotential (eta) and the straight coefficient of the electrode (L(EE)).
• The degree of coupling between catabolism and the ORP electrode is also identified as a key factor.

Conclusions:

• The MIRROR model provides a novel framework for quantifying ORP in nonequilibrium biological systems, overcoming limitations of the Nernst equation.
• The model highlights the direct proportionality between metabolic energy expenditure and specific thermodynamic parameters.
• Further discussion on the limitations of MIRROR Model No. 1 is provided to guide future applicability and model expansion.