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ANTIMICROBIAL ACTIVITY OF COPPER AND ZINC ACCUMULATED BY EASTERN OYSTER AMEBOCYTES
Fisher, W S. ANTIMICROBIAL ACTIVITY OF COPPER AND ZINC ACCUMULATED BY EASTERN OYSTER AMEBOCYTES. JOURNAL OF SHELLFISH RESEARCH 23(2):321-351, (2004).
To present findings that demonstrate a strong affinity of oyster amebocytes for copper and zinc, prolonged retention of the metals despite an available route of elimination, and strong circumstantial evidence of antimicrobial activity by accumulated copper and zinc
Fisher, William S. Submitted. Antimicrobial Activity of Copper and Zinc Accumulated by Eastern Oyster Amebocytes. J. Shellfish Res. 54 p. (ERL,GB 1196).
The distribution of eastern oysters Crassostrea virginica near terrestrial watersheds has led to a general impression that low or variable salinity is imperative for survival. However, freshwater runoff contains numerous mineral elements from geologic deposits that could play significant roles in oyster physiology. Two metals of terrestrial origin, copper and zinc, are accumulated to extremely high concentrations in eastern oysters, even in the absence of anthropogenic sources. As yet, there has been no defendable demonstration of a physiological function for such high concentrations of copper and zinc. Both, however, are accumulated almost exclusively in the amebocytes and calcareous shell of oysters, a unique distribution that implicates a role in at least one of the many functions of amebocytes. Amebocytes are migratory, diapedetic cells recognized primarily for providing nutriment and defense through phagocytosis, killing and digestion of invading or ingested microorganisms. There is sufficient evidence in the existing literature to suggest that copper and zinc directly contribute to these antimicrobial activities. This review presents historical and recent findings that demonstrate a strong affinity of oyster amebocytes for copper and zinc (even in low ambient concentrations), prolonged retention of the metals despite an available route of elimination, and strong circumstantial evidence of antimicrobial activity by accumulated copper and zinc. It is proposed that oysters actively concentrate copper and zinc as toxic antimicrobial agents to be used in intracellular and extracellular killing as well as extracellular clot formation (precipitation of hemolymph). This potential, combined with evidence of amebocyte deposition of oyster shell, provides an alternative framework for interpretation of amebocyte activities and coastal distributions of oyster populations. It also affords some resolution to the apparent contradiction of eastern oysters thriving at relatively polluted locations.