Toluene Induction and Uptake Kinetics and Their Inclusion in the Specific-Affinity Relationship for Describing Rates of Hydrocarbon Metabolism

Abstract

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, = 44 ,ug/liter) and large specific affinity. Kinetics for Pseudomonas putida PpF1 were similar. Induction had little effect on K,, 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 Kind was 96 ,ug/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-2,4dienoic 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.

Toluene degradation kinetics for planktonic and biofilm‐grown cells of Pseudomonas putida 54G

“…Values of specific activities (SAB) decreased from 0.25 to about 0.025 mg/mg h at the end of the experiment, while SAH decreased initially to 2.4 × 10 −10 mg/cfu h in 1.5 days and then decreased only slightly to about 2.25 × 10 −10 mg/cfu h at the end of the experiment at 26 days. The initial drop in SAH (day 1 to day 2) was characteristic of a stationary phase decline in activity (Robertson and Button, 1987; despite the continuing supply of toluene and oxygen), while cell numbers on HT plates remained nearly constant. The onset of injury in this experiment was at approximately 1 day, which correlated with transition of the cells from a log-phase culture to a stationary-phase culture.…”

Inability of bacteria to degrade low concentrations of toluene in water

“…Similarly, Law and Button [15] observed an increase in toluene metabolism by bacteria in the presence of benzene. In contrast, it is possible that the synthesis of enzymes required for toluene metabolism was repressed during the degradation of ethanol, butanol, or glucose or that the concentration of toluene might have been too low to induce the synthesis of these enzymes [7,8].…”

“…If the concentration of a chemical is too low to induce the synthesis of enzymes required for metabolism of the compound in the cells, then the degradation of that compound may be slow or fail to occur even if the population of bacteria is large. Robertson and Button [7] reported that the minimum concentration of toluene above which an increase in activity would occur could be as high as 132 μg/L, and Reber [8] reported that 3‐chlorobenzoate could induce its degradation by Acinetobacter calcoaceticus only at concentrations above 157 μg/L.…”

Degradation of toluene by a mixed population of archetypal aerobes, microaerophiles, and denitrifiers: Laboratory sand column experiment and multispecies biofilm model formulation

“…Organic pollutants are frequently found in aquifers where the dissolved oxygen concentration is usually low. Aromatic pollutants such as benzene, toluene, ethylbenzene, and xylene (BTEX) are degraded aerobically by means of oxygenasecatalyzed reactions, which require molecular oxygen for the hydroxylation of the aromatic ring, or an alkyl substitution (Assinder and Williams, 1990;Gibson et al, 1970;Robertson and Button, 1987;Shields et al, 1989). In the biodegradation of hydrocarbons, oxygen acts both as a co-substrate of the oxygenase enzyme and as a terminal electron acceptor for cellular respiration.…”