Mechanisms Of Resistance to Polychlorinated Biphenyls (PCB) in Two Species of Marine Diatoms

Abstract

Clones of Ditylum brightwellii and Thalassiosira nordenskioldii were isolated from New York coastal waters, and PCB-resistance in D. brightwellii was induced in the laboratory by exposure to increasing concentrations of PCB. Resistance could not be similarly induced in T. nordenskioldii, but was serendipitously discovered in unexposed cultures that had undergone sexual reproduction.Cells of the resistant strain were substantially larger than those of the sensitive strain in both species. Larger vacuole space seemed to account for this in D. brightwellii, but in T. nordenskioldii larger cells contained more carbon. Experiments with14C-PCB tracer indicated that PCB accumulation was less in resistant strains of both species. Neutral lipid content per cell, as determined using the fluorophore Nile Red, was similar for resistant and sensitive strains of both species. Sub-cellular examination of lipid droplets in D. brightwellii suggested that the PCB-resistant strain may be sequestering this lipophilic toxicant in a location removed from physiological activity. In T. nordenskioldii a decreased ratio of neutral lipidxarbon may reduce intracellular accumulation of PCB. These diatom species have developed PCB resistance in the highly PCB-polluted Hudson River estuary and, since they are the preferred food of dominant copepods, they may offer less PCB per unit ration to zooplankton grazers.