Limited Mechanistic Link Between the Monod Equation and Methanogen Growth: a Perspective from Metabolic Modeling

Area of Science:

• Microbial Physiology
• Metabolic Engineering
• Biochemical Kinetics

Background:

• The Monod equation is a cornerstone for modeling microbial growth rates.
• However, its predictive accuracy is limited in various biological contexts.
• Understanding the mechanistic basis of microbial growth kinetics is crucial.

Purpose of the Study:

• To investigate the limitations of the Monod equation in describing methanogen growth kinetics.
• To explore the roles of enzymes and metabolites in controlling microbial growth rates across different substrate concentrations.
• To unify competing views on enzyme contributions to growth dynamics.

Main Methods:

• Utilized kinetic and stoichiometric metabolic models.
• Applied metabolic control analysis frameworks.
• Simulated growth kinetics of a methanogenic microorganism.

Main Results:

• Identified that different enzymes and metabolites exert varying degrees of control over growth rate.
• Demonstrated that these controls peak at low, intermediate, or high substrate concentrations.
• Showed the Monod equation approximates controls only at very low and very high concentrations, neglecting intermediate effects.

Conclusions:

• Established a limited mechanistic link between the Monod equation and methanogen metabolic networks.
• Highlighted that single-term rate expressions may be insufficient for accurate microbial growth prediction.
• Supported the Monod equation as a useful, albeit approximate, model for microbial kinetics.