INFLUENCE OF ORGANIC-LIGANDS ON THE TOXICITY OF COPPER TO PSEUDOMONAS-SYRINGAE

Pseudomonas syringae cells were exposed to CU2+ alone or in the presen ce of acetate, proline or cysteine, at concentrations that reduced fre e CU2+ to 1/10 Of the total copper. Ligand concentrations (designated as isoeffective) were determined experimentally using a Cu2+-selective electrode and confirmed by computer calculations using published stab ility constants. Exposure of P. syringae cells to CU2+ alone resulted in rapid and pronounced cell death, and binding of most of the copper in solution. The addition of acetate, proline or cysteine, a few minut es after CU2+ treatment, resulted in a significant reduction in cell d eath, and in the amount of copper bound to the cells. For short exposu res to CU2+, cysteine was more effective than acetate or proline, but after 60 min of treatment, similar results were observed with these li gands. The addition of ligands before Cu2+ resulted in even more reduc ed copper toxicity. The results showed that, at isoeffective concentra tions, weak and moderate copper-ligands can effectively antagonize cop per toxicity, and that this protective effect does not require previou sly equilibrated copper-ligand solutions and is not very dependent of the nature of the ligand.