SUBSTRATE AVAILABILITY IN PHENANTHRENE BIODEGRADATION - TRANSFER MECHANISM AND INFLUENCE ON METABOLISM

The mechanism of phenanthrene transfer to the bacteria during biodegra dation by a Pseudomonas strain was investigated using a sensitive resp irometric technique (Sapromat equipment) allowing the quasicontinuous acquisition of data on oxygen consumption. Several systems of phenanth rene supply, crystalline solid and solutions in non-water-miscible sol vents (silicone oil and 2,2,4,4,6,8,8-heptamethylmonane) were studied. In all cases, analysis of the kinetics of oxygen consumption demonstr ated an initial phase of exponential growth with the same specific gro wth rate. In order to analyze the second phase of growth and phenanthr ene degradation, a study of the kinetics of phenanthrene transfer to t he aqueous phase was conducted by direct experimentation, with the cry stal and silicone oil systems, in abiotic conditions. The data allowed the validation of a model based on phase-transfer laws, describing th e variations, with substrate concentrations, of rates of phenanthrene transfer to the aqueous phase. Analysis of the biodegradation curves t hen showed that exponential growth ended in all cases when the rates o f phenanthrene consumption reached the maximal transfer rates. Thereaf ter, the biodegradation rates closely obeyed, for all systems, the tra nsfer rate values given by the model. These results unambiguously demo nstrated that, in the present case, phenanthrene biodegradation requir ed prior transfer to the aqueous phase. With the silicone oil system, which allowed high transfer and biodegradation rates, phenanthrene was directed towards higher metabolite production and lower mineralizatio n, as shown by oxygen consumption and carbon balance determinations.