15. The Effect of Various Metal Ions on Bio-hydrogen Production and F₀F₁-ATPase Activity of Rhodobacter Sphaeroides

The important aspect in regulation of bio-hydrogen (H₂) production by purple bacteria and its energetics is the requirement of the F₀F₁-ATPase, the main membrane mechanism generating proton motive force. Rhodobacter sphaeroides MDC 6521 (isolated from Arzni mineral springs in Armenia) is able to produce H₂ in anaerobic conditions under illumination in the presence of various metal ions. In order to examine the mediatory role of the F₀F₁-ATPase in H₂ production, the effects of various metal ions (Mn²⁺, Mg²⁺, Fe²⁺, Ni²⁺, and Mo⁶⁺) on N,N′-dicyclohexylcarbodiimide inhibited ATPase activity of R. sphaeroides membrane vesicles were investigated. These ions in appropriate concentrations considerably enhanced H₂ production. But the latter was not observed in the absence of Fe²⁺, indicating the requirement of Fe²⁺. The R. sphaeroides membrane vesicles demonstrated significant ATPase activity. The absence of Fe²⁺ caused to marked inhibition (~80 %) in ATPase activity. In the presence of Fe²⁺ (80 μM) and Mo⁶⁺ (16 μM) a higher ATPase activity was observed. These results indicate a relationship between H₂ production and the F₀F₁-ATPase activity that might be an important pathway to regulate bacterial activity under anaerobic conditions and provide novel evidence on responsibility of F₀F₁ in H₂ production by R. sphaeroides.