Copper toxicity to cyanobacteria and its dependence on extracellular ligand concentration and degradation.

Copper toxicity to the cyanobacteriumPlectonema boryanum (UTEX 594) has been investigated in the presence of citrate and nitrilotriacetic acid (NTA) using a copper-saturated culture medium. The coppercitrate complex was biodegradable, and toxicity was dependent on the free ligand concentration. The ratio of citrate to copper also affected the extent of metal toxicity. NTA was not degraded byP. boryanum. Ligand degradation in the cyanobacterial culture increased the ionic copper concentration and caused a concomitant reduction in growth. The ecological implications of these findings are discussed.