Interactive regulation of dissolved copper toxicity by an estuarine microbial community

Cultured marine microorganisms under copper stress produce extracellular compounds having a high affinity for copper (copper‐complexing ligands). These ligands are similar in binding strength to those found in natural waters, but few studies have examined the relationship between copper, copper‐complexing ligand concentrations, and natural microbial populations. A series of in situ experiments in the Elizabeth River, Virginia, revealed that an intact estuarine microbial community responded to copper stress by production of extracellular, high‐affinity copper complexing ligands. The rate of ligand production was dependent on copper concentration and resulted in a reduction of the concentration of free cupric ions, Cu2+, by more than three orders of magnitude during a 2‐week period in one experiment. We believe that this interactive response to copper stress represents a feedback system through which microbial communities can potentially buffer dissolved Cu2+ ion concentrations, thereby regulating copper bioavailability and toxicity.