Effects of copper and nickel on the growth of nitrosomonas europaea

The toxic effects of copper(II) and nickel(II) species on the growth of Nitrosomonas europuea were investigated. The initial conditions of media were defined in terms of chemical speciation using a chemical equilibrium model. The investigation measured the response of N. europaea (the oxidation of ammonium to nitrite) cultured in a simple medium containing five cations (Ca2+, Mg2+, Fe2+, K+, Na+ ) and five inorganic ligands (CO2−3, SO2−4, Cl−, PO3−4, OH−), to changing concentrations of heavy metals (Cu2+, Ni2+) and total ammonia (NH3 plus NH+4). Experimental conditions were controlled as to allow interpretation of the results in terms of chemical species and their toxic effects on the organisms. Decrease of the specific growth rate of N. europaea was linearly correlated (r≥ 0.90) with the logarithmic activities of Cu(II)-ammine species (i.e., CuNH2+3, Cu(NH3)2+2, Cu(NH3)2+3, Cu(NH3)2+4,), regardless of the total copper(II) activity in the medium. Nickel(II) was far less toxic than copper(II) on the basis of specific growth rate, but nickel induced a lag or synchronized growth on the culture. The duration of lag increased with increasing total nickel concentration, while it decreased significantly as total ammonia concentration increased. The lag time was highly correlated (r>0.85) with total nickel and Ni2+ activities on log-log scale at high ammonia concentrations, but no particular nickel species was implicated as the toxic agent. The toxicity of copper and nickel were markedly influenced by the substrate concentration.