OXYGEN-CONSUMPTION IN THE MARINE BACTERIUM PSEUDOMONAS-NAUTICA PREDICTED FROM ETS ACTIVITY AND BISUBSTRATE ENZYME-KINETICS

The respiratory O-2 consumption in aerobic bacterial cultures has been modeled from the time profiles of the in vitro activity of the respir atory electron transfer system (ETS), the bacterial protein and the co ncentration of the carbon source in the cultures The model was based o n the concept of bisubstrate kinetic control of the ETS throughout the exponential, steady-state and senescent phases of the cultures. In th e exponential phase, the measured rates of O-2 consumption and the in vitro ETS activity were closely coupled, but in the senescent phase, t hey were uncoupled. The in vitro ETS activity remained high even after the culture's carbon source was exhausted, while the O-2 consumption fell to low levels. Based on the hypothesis that this uncoupling was c aused by limitation of the intracellular ETS substrates (NADH and NADP H), a semi-empirical model incorporating a bisubstrate enzyme kinetics algorithm was formulated and fitted to the observations of the experi ments. The model predicted the rate of O-2 consumption throughout the different phases of the cultures with an r(2) > 0.92 (n = 9, P < 0.001 ) using physiologically realistic Michaelis and dissociation constants . These results suggest that plankton respiration in the field could b e assessed more accurately than before by measuring the intracellular ETS substrates (NADH and NADPH), in addition to ETS activity, in plank ton.