Inhibitory effects of copper on bacteria related to the free ion concentration

Cu²⁺ ion determinations were carried out in complex and in inorganic salts-glycerol media, to which increasing amounts of Cu(II) had been added, with the ion-specific Cu(II)-Selectrode. Likewise, complexing capacity of bacterial suspensions was estimated by titration with CuSO₄. Copper-sensitive bacteria, e.g., Klebsiella aerogenes, were inhibited in their growth and survival in the range of 10^-8-10^-6 M Cu²⁺ ion concentrations. In copper-buffered complex media, high copper loads could be tolerated, as growth proceeded with most of the copper bound to medium components. In low-complexing mineral salts media, in which high Cu²⁺ ion concentrations exist at low copper loads, there was competition of Cu²⁺ for binding sites of the cells. Total allowed copper was then determined by the ratio of copper to biomass. Copper-resistant bacteria could be isolated from a stock solution of CuSO₄, containing 100 ppm Cu(II). They were of the Pseudomonas type and showed a much higher tolerance towards Cu²⁺, up to 10^-3 M.