CO₂ production rate predicted from isocitrate dehydrogenase activity, intracellular substrate concentrations and kinetic constants in the marine bacterium Pseudomonas nautica

Abstract.

CO₂ production rates in all growth phases of the marine bacterium Pseudomonas nautica have been modeled using bisubstrate enzyme kinetics, isocitrate dehydrogenase activity and measurements of intracellular isocitrate and NADP⁺. The mathematical model has been adapted from a previous publication and modified by incorporating newly measured kinetic constants, and new experimentally determined algorithms for intracellular isocitrate and NADP⁺. The model can predict the rate of CO₂ production for up to 14 days and successfully describes the transition from exponential growth to senescence that occurs within the first 24 h as the organic nutrient source is depleted. A single substrate kinetic model of the rate of CO₂ production was also tested, but was found to be less descriptive of the observations than the bisubstrate model. Future improvement of the model should account for variations of the physiological culture conditions, a revision of the isocitrate algorithm, and the addition of malic enzyme and phophoenolpyruvate carboxykinase terms.