A mathematical model correlating catabolic gene activity with biodegradation rates using a bioluminescent reporter strain

A structured genetic mathematical model has been developed for the bioluminescent reporter strain HK44. This Pseudomonas fluorescens strain contains a nah-lux gene fusion. The nah genes encode for enzymes that degrade naphthalene, and Iux genes encode for light emitting luciferase enzymes. This strain emits light and degrades naphthalene when induced by salicylate, an intermediate product of naphthalene degradation. A positively regulated operator-promoter controls this gene fusion. This model relates bioluminescence to naphthalene exposure at the gene regulatory level. The model consists of mass balances on DNA, mRNA and enzymes. A comparison between experimental data and simulations of the model indicates that the bioluminescent response to naphthalene exposure is not the sole function of a single transcriptional regulation system. The bioluminescent response of the strain HK44 appears to be at least a second-order dynamic process. The second-order dynamic response of HK44 to naphthalene exposure may be the additive response of two first-order dynamic processes. The nah-lux regulatory system may be one of the first-order processes, and the fatty acid regulatory system may be the other. The fatty acid regulatory system may vary its production of fatty acids (one of the reactants involved in bioluminescence) in response to the present of naphthalene in its surroundings. This adaptive response could explain the response of the strain HK44 to naphthalene exposure. Further experimentation could verify this hypothesis, and the mathematical model could be further developed to incorporate both regulation processes. This study also used the reporter strain as a tool to study naphthalene degradation in a packed bed reactor. Fiber optic bundles or liquid light pipes were inserted through the ports drilled through the walls of the packed-bed reactor. This facilitated the bioluminescence measurement in the packed-bed reactor. Bioluminescent measurements indicate that naphthalene degradation activity occurs primarily at the reactor's inlet. Light measurements also indicate that higher flowrates produce a shorter effective biodegradative zone in the packed bed. A packed-bed model consisting of naphthalene, oxygen, and biomass mass balances resulted in a coupled system of one ordinary and three non-linear partial differential equations. These equations were solved numerically using the three-point backward finite difference technique. Simulations of the packed bed reactor indicate that the hydraulic flowrate is one of the most important parameters affecting biodegradation kinetics. At slower flowrates diffusion is the dominant mass transport mechanism in the packed bed reactor. As the flowrate increases, convection dispersion becomes the dominant mass transport mechanism. This results in higher mass transport rates to the biofilm, which facilitates more biofilm growth at the reactor's inlet. As a result the active degradative zone in the packed bed occurs at the inlet and it is small (< 0.75 cm).