Influence of metals on oxygen uptake, carbon dioxide fixation, and cytochrome reduction in Nitrobacter Agilis

Oxygen uptake coupled with nitrite oxidation by washed cell suspensions of Nitrobacter agilis was tested in the presence of copper, nickel, aluminum, uranyl, and molybdate ions. Copper ion was slightly stimulatory at low concentrations and strongly inhibitory at 17 mM. Molybdate ion showed either slight enhancement or no inhibition at all test concentrations. With the other test ions, inhibition of oxygen uptake was observed. Carbon dioxide fixation was generally more sensitive to metal ions than was oxygen uptake. Cytochrome reduction in washed cells of N. agilis was demonstrated in the presence and absence of metal ions. Cytochrome aa3 and cytochrome a1 (α-peak at 590 nm) were sensitive to aluminum, uranyl, and molybdate ions, whereas cytochrome c (β-peak at 520 nm) was insensitive to test ions. All metal ions inhibited the reduction of cytochrome a1 (γ-peak at 438 nm). This inhibition decreased when the concentration of copper and molybdate was increased to 1.7 mM. Only aluminum and nickel ions demonstrated a concentration-dependent inhibition of cytochrome a1 (438 nm). The test ions blocked the activity of cytochrome c (α-peak at 550 nm). The inhibition of cytochrome c at 415 nm (γ-peak) was also apparent.