At 10 mM, Cu+ was highly protective against killing of spores of Bacil
lus megaterium ATCC 19213 by H2O2, while at higher concentrations, fro
m 15-100 mM, killing was augmented. In contrast, Cu2+, Fe2+, Fe3+, Co2
+ Or Co3- ions acted only protectively. Cu+ itself was sporicidal in t
he absence of H2O2 or ascorbate, and its sporicidal action did not dep
end on generation of highly reactive oxygen species. It appeared that
killing involved either inhibition of germination or copper toxicity t
o germinated cells in that Cu+-inactivated spores did not germinate re
adily but chemical decoating of the cells prior to plating on a solid
medium resulted in reversal of the sporicidal effect.