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JOURNAL OF PLANKTON RESEARCH | VOLUME 18 | NUMBER 10 | PAGES 1819-1835 | 1996
© Oxford University Press
research-article |
Oxygen consumption in the marine bacterium Pseudomonas nautica predicted from ETS activity and bisubstrate enzyme kinetics
Institut Maurice-Lamontagne CP1000, Mont-Joli Quebec, G5H 3Z4, Canada 1Institut de Ciencias Marinas Passeig Juan Borbó c/n, 08030 Barcelona, Spain 2329 Rte 298 Sud, St-Donat de Rimouski, Quibec, GOK 1L0 3Département d'Océanologie, Université du Québec à Rimouski 300 allée des Ursulines, Rimouski, Quibec, G5L 3A1, Canada
Received on January 17, 1996; accepted on May 2, 1996 The respiratory O2 consumption in aerobic bacterial cultures has been modeled from the time profiles of the in vitro activity of the respiratory electron transfer system (ETS), the bacterial protein and the concentration of the carbon source in the cultures. The model was based on the concept of bisubstrate kinetic control of the ETS throughout the exponential, steady-state and senescent phases of the cultures. In the exponential phase, the measured rates of O2 consumption and the in vitro ETS activity were closely coupled, but in the senescent phase, they were uncoupled. The in vitro ETS activity remained high even after the culture's carbon source was exhausted, while the O2 consumption fell to low levels. Based on the hypothesis that this uncoupling was caused by limitation of the intracellular ETS substrates (NADH and NADPH), a semi-empirical model incorporating a bisubstrate enzyme kinetics algorithm was formulated and fitted to the observations of the experiments. The model predicted the rate of O2 consumption throughout the different phases of the cultures with an r2 > 0.92 (n = 9, P < 0.001) using physiologically realistic Michaelis and dissociation constants. These results suggest that plankton respiration in the field could be assessed more accurately than before by measuring the intracellular ETS substrates (NADH and NADPH), in addition to ETS activity, in plankton.
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