The Rhodobacter sphaeroides F0F1-ATPase activity: Effects of heavy metal ions and relationship with hydrogen photoproduction

Abstract

The important aspect in regulation of hydrogen (H2) photoproduction by purple bacteria and its energetics is the requirement of the F0F1-ATPase, the main membrane mechanism generating proton motive force [1,2]. Previously the relationship between H2 production, proton transport and the F0F1-ATPase activity was shown by purple bacteria Rhodobacter sphaeroides [2]. It is well known that H2 production varies depending on the different factors: anaerobic conditions, light intensity, pH, carbon and nitrogen sources, and heavy metals ions [3,4]. Fe, Ni and Mo ions are the components of enzymes, which are responsible for H2 production by photosynthetic bacteria, such as hydrogenase and nitrogenase. Bacterial photosynthetic pigments such as bacteriochlorophyll contain Mg. R. sphaeroides MDC 6521 (isolated from Arzni mineral springs in Armenia) is able to grow and produce H2 in anaerobic conditions under illumination in the presence of various heavy metal ions [4]. In this study in order to examine the mediatory role of the F0F1-ATPase in H2 production, the effects of metal ions (Ni, Mg, Mo, and Fe) on DCCD inhibited ATPase activity of R. sphaeroides membrane vesicles were investigated. These metal ions in appropriate concentrations considerably enhanced H2 production by R. sphaeroides. But H2 production was not observed in the absence of Fe, indicating that Fe is required for H2 production. As was shown in our previous study [2] the R. sphaeroides membrane vesicles demonstrated significant ATPase activity. The absence of Fe caused to marked inhibition (~80%) in ATPase activity. After treatment of membrane vesicles with Ni (0.004 mM) and Mg (10 mM) the ATPase activity stimulation was observed: the activity was increased by 15 and 30%, respectively. The Fe (0.08 mM) and Mo (0.016 mM) added gave a stimulated (~2.5 fold) ATPase activity. These results indicate a relationship between the F0F1-ATPase activity and H2 photoproduction. This provides novel evidence on the role of the F0F1-ATPase in H2 production by this bacterium.