The Effects of Copper (II) Ions on Enterococcus hirae Cell Growth and the Proton-Translocating F0F1 ATPase Activity

Enterococcus hirae grow well under anaerobic conditions at alkaline pH (pH 8.0) producing acids by glucose fermentation. Bacterial growth was shown to be accompanied by decrease of redox potential from positive values (similar to+35 mV) to negative ones (similar to-220 mV). An oxidizer copper (II) ions (Cu2+) affected bacterial growth in a concentration-dependent manner (within the range of 0.05 mM to 1 mM) increasing lag phase duration and decreasing specific growth rate. These effects were observed with the wild-type strain ATCC9790 and the atpD mutant strain MS116 (with absent beta subunit of F-1 of the F0F1 ATPase) both. Also ATPase activity and proton-potassium ions exchange were assessed with and without N,N'-dicyclohexylcarbodiimide (DCCD), inhibitor of the F0F1 ATPase. In both cases (DCCD +/-), even low Cu2+ concentrations had noticeable effect on ATPase activity, but with less visible concentration-dependent manner. Changes in the number of accessible SH-groups were observed with E. hirae ATCC9790 and MS116 membrane vesicles. In both strains Cu2+ markedly decreased the number of SH-groups in the presence of K+ ions. The addition of ATP increased the amount of accessible SH-groups in ATCC9790 and decreased this number in MS116; Cu2+ blocked ATP-installed increase in SH-groups number in ATCC9790. H+-K+-exchange of bacteria was markedly inhibited by Cu2+, but stronger effects were detected together with DCCD. Moreover, discrimination between Cu2+ and other bivalent cation-Ni2+ was shown. It is suggested that Cu2+ ions inhibit E. hirae cell growth by direct affect on the F0F1 ATPase leading to conformational changes in this protein complex and decrease in its activity.