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

Cu(2+) 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 Cu(2+) 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 Cu(2+) ion concentrations exist at low copper loads, there was competition of Cu(2+) 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 thePseudomonas type and showed a much higher tolerance towards Cu(2+), up to 10(-3) M.