Inhibition of transformation of Bacillus subtilis by ethidium bromide.

Incubation of donor DNA with ethidium bromide before addition to competent cells, strongly inhibited chromosomal transformation, plasmid transfer and phage-SPP1 DNA mediated transfection. There was no effect of the dye on the binding and entry of DNA into the cells. Analysis of the fate of transforming DNA treated with ethidium bromide showed a reduction in the amount of donor DNA associated with the recipient chromosome. The formation of this donor-recipient complex seems to be slowed down by the dye.