Copper toxicity in Erwinia amylovora: An X-ray microanalytical study

The effect of Cu 2+ ions on the growth and elemental composition of the phytopathogenic bacterium Erwinia amylovora was investigated by in vitro culture in nutrient broth supplemented with CuSO 4. No detectable inhibition in bacterial growth occurred with medium supplemented at 10 -4M Cu (compared to control medium with no added Cu), but partial inhibition occurred at 10 -3M Cu (limiting toxicity) and complete inhibition at 10 -2M Cu. Under conditions of limiting toxicity, incubation in Cu 2+ ions leads to a reduction in the general synthesis of cell materials and the formation of abnormally large cells with a small dry mass. X-ray analysis revealed the uptake of small levels of Cu 2+ under these conditions, plus wide-ranging changes in other major elements present in the bacterial cells. These changes included a reduction in the level of K and increased levels of the divalent cations Ca and Fe. The results obtained are consistent with the toxic effect of Cu being mediated via its effect on the cell membrane, with internal elemental changes resulting from a perturbation of membrane permeability.