Toluene induction and uptake kinetics and their inclusion in the specific-affinity relationship for describing rates of hydrocarbon metabolism.
The kinetics of concentration-dependent toluene metabolism were examined by evaluating each term in the second-order rate equation. Marine and freshwater pseudomonads were used. Uptake for Pseudomonas sp. strain T2 was characterized by a completely saturatable system with small transport constant (K(t) = 44 mug/liter) and large specific affinity. Kinetics for Pseudomonas putida PpF1 were similar. Induction had little effect on K(t), but it caused the specific affinity to increase from about 0.03 to 320 liters/g of cells per h. The level of induction depended on the time of exposure, the concentration of inducer, and the initial level of induction. If loss of the inducible system was not severe, toluene caused a linear increase in specific affinity with time, and the maximal value achieved at intermediate times (1 to 3 days) was hyperbolic with concentration when K(ind) was 96 mug/liter (A. T. Law and D. K. Button, Appl. Environ. Microbiol. 51:469-476, 1986). As repression became complete, specific affinities were greatly reduced. Then induction required higher toluene concentrations and longer times, and the shape of the specific-affinity curve became sigmoidal with concentration. Cell yields (0.10 to 0.17 g of cells per g of toluene used) were low owing to liberation of organic products: 2-hydroxy-6-oxohepta-2,4-dienoic acid, toluene dihydrodiol, 3-methylcatechol, acetate, formate, and possibly pyruvate, which in turn caused lower rates of growth. Michaelis constants for the reaccumulation of products exceeded those for toluene, but specific affinities were lower and maximal velocities were higher, so that recycling was favored in cultures with high toluene concentration. Although these kinetics predict deviation from the linear relationship between uptake rate and biomass, we could detect none. Effects of saturation and induction were incorporated into the basic specific-affinity relationship. The result appears to be an improvement in the equation used for describing the kinetics of uptake and growth.
Robertson
B R
BR
Institute of Marine Science, University of Alaska, Fairbanks, Alaska 99775-1080.
Button
D K
DK