Limited microbial degradation of pyrene metabolites from the estuarine polychaete Nereis diversicolor

We compared microbial mineralization of [4,5,9,10- ¹⁴C]pyrene and its eukaryotic [4,5,9,10-¹⁴C]pyrene metabolites in estuarine sediments. Metabolites were obtained by exposing the estuarine deposit-feeding polychaete Nereis diversicolor to sediment-associated ¹⁴C-pyrene, followed by homogenization of the worms and extraction of the pyrene-metabolites. In sediment from a pristine Danish Fjord only 2.6% of the added metabolite-label and 1.7% of the pyrene-label were mineralized to ¹⁴CO₂ during 175 days incubation. Pre-exposure of the pristine sediment to unlabelled pyrene for 60 days increased the mineralization potential for ¹⁴C-pyrene substantially, as 81.2% was mineralized to ¹⁴CO₂ during 95 days incubation, whereas ¹⁴C-pyrene metabolite label was unaffected by pre-exposure to pyrene. In comparison, naturally aged bunker-oil contaminated sediment did not show elevated potentials for mineralization of neither ¹⁴C-pyrene nor ¹⁴C-metabolites. Six bacterial strains of known pyrene degraders were tested for growth on crystalline 1-hydroxypyrene. 1-Hydroxypyrene is the only intermediate eucaryotic metabolite of pyrene. The results indicate that 1-hydroxypyrene was not utilized as a sole source of carbon and energy by any of them. In addition, respiration was depressed in all six strains when exposed to crystalline 1-Hydroxypyrene, demonstrating an acute toxic effect of 1-hydroxypyrene. The results presented here suggest that microbial degradation of pyrene is not enhanced by release of aqueous and polar metabolites by marine invertebrates.