CO2 PRODUCTION PREDICTED FROM ISOCITRATE DEHYDROGENASE-ACTIVITY AND BISUBSTRATE ENZYME-KINETICS IN THE MARINE BACTERIUM PSEUDOMONAS-NAUTICA

CO2 production in aerobic bacteria was modeled from the time-courses o f the in vitro activity of isocitrate dehydrogenase (IDH), bacterial p rotein, and the concentration of the carbon source in the cultures. Th e model was based on the concept of bisubstrate control of the IDH rea ction through out the exponential, steady-state, and senescent phases of the cultures. In the exponential phase, the measured rates of CO2 p roduction and the in vitro IDH activity were closely coupled, but in t he senes-cent phase, they became uncoupled. The in vitro IDH activity remained high even after the culture's carbon source was exhausted, wh ile the CO2 production fell to low levels. Based on the hypothesis tha t this uncoupling was caused by internal substrate limitation, 2 mathe matical models incorporating a bisubstrate enzyme kinetics algorithm w ere constructed and tested. The models predicted the rate of CO2 produ ction throughout the different phases of the cultures with an r(2) gre ater than 0.84.