The effects of manganese (II) but not nickel (II) ions on Enterococcus hirae cell growth, redox potential decrease, and proton-coupled membrane transport

Enterococcus hirae grow well under anaerobic conditions by fermenting glucose, accompanied with the decrease of oxidation-reduction potential (Eh) from positive values to negative ones. It was shown that heavy metals-copper and iron ions-affect E. hirae growth and alter Eh and proton-potassium ions fluxes through the cell membrane. The aim of this study was to establish the effects of manganese (II) ions on bacterial growth within the concentration range of 0.01-1 mM and compare with nickel (II) ions' effect. The presence of Mn(2+) during E. hirae ATCC9790 growth had significant effects: The lag phase duration decreased while the specific growth rate was increased; decrease in E h was shifted. In contrast, no visible changes in bacterial growth and Eh were observed in the case of Ni(2+). The effects of these ions on proton-potassium ions fluxes through the cell membrane were estimated in the presence and absence of N,N'-dicyclohexylcarbodiimide (DCCD), inhibitor of the FoF1 ATPase. Stronger effect of Mn(2+) on H(+)-K(+) exchange was detected in the presence of DCCD that can be explained by a possible complex formation between these substances and its direct influence on membrane transport proteins.