INTERFERENCE OF COPPER SULFATE WITH GROWTH OF ERWINIA AMYLOVORA AND MONITORING BACTERIAL PROPAGATION IN PLANTA

Copper salts have been widely used to control spread of fire blight.
When cultured in minimal medium without amino acids, copper sulfate was inhibitory for growth of Erwinia amylovora at concentrations above 10 μM. The addition of 4 g asparagine per liter relieved the toxic effect and allowed growth of the bacteria even at 2 mM CuSO₄. In contrast to streptomycin, the growth inhibition by CuSO₄ was not correlated to a fast bacterial cell death.
Copper ions caused a pH-shift at concentrations above 2 mM in weakly buffered medium.
Complexed with Tris or citrate, a differential effect of these complexes was assayed with E. amylovora cells expressing the lux-operon of Vibrio fischeri. Bioluminescence depends on the ATLP content of the bacteria and is thus an efficient indicator for the stage of cell metabolism.
This system was also applied to trace E. amylovora for movement on leaves of quince or in stems of apple seedlings down into parts of the roots.

Copper sulfate in solidified minimal medium with asparagine caused formation of yellow colonies and induced synthesis of the acidic exopolysaccharide (EPS) amylovoran. E. amylovora strains became copper-resistant when grown at 4 mM, and their EPS-synthesis was dependent on copper ions in the medium.
On pear seedlings or pear slices, they were still virulent.
The complex formation of copper ions with various components may influence the application of sprays with copper-ions for control of fire blight.
The toxic effect may also be changed by compounds of the host-plants.

VII International Workshop on Fire Blight

S. Bereswill, I. Bruchmuller, K. Geider

https://doi.org/10.17660/ActaHortic.1996.411.40