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 (E _h) from positive values to negative ones. It was shown that heavy metals—copper and iron ions—affect E. hirae growth and alter E _h 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 Mn²⁺ 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 E _h were observed in the case of Ni²⁺. 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 F_oF₁ ATPase. Stronger effect of Mn²⁺ 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.