Relationship of proton motive force and the F^sub 0^F^sub 1^-ATPase with bio-hydrogen production activity of Rhodobacter sphaeroides: effects of diphenylene iodonium, hydrogenase inhibitor, and its solvent dimethylsulphoxide

Rhodobacter sphaeroides MDC 6521 was able to produce bio-hydrogen (H2) in anaerobic conditions under illumination. In this study the effects of the hydrogenase inhibitor--diphenylene iodonium (PH2I) and its solvent dimethylsulphoxide (DMSO) on growth characteristics and H2 production by R. sphaeroides were investigated. The results point out the concentration dependent DMSO effect: in the presence of 10 mM DMSO H2 yield was ~6 fold lower than that of the control. The bacterium was unable to produce H2 in the presence of PH2I. In order to examine the mediatory role of proton motive force ([increment]p) or the F^sub 0^F^sub 1^-ATPase in H2 production by R. sphaeroides, the effects of PH2I and DMSO on [increment]p and its components (membrane potential ([increment]ψ) and transmembrane pH gradient), and ATPase activity were determined. In these conditions [increment]ψ was of -98 mV and the reversed [increment]pH was +30 mV, resulting in [increment]p of -68 mV. PH2I decreased [increment]ψ in concentrations of 20 μM and higher; lower concentrations of PH2I as DMSO had no valuable effect on [increment]ψ. The R. sphaeroides membrane vesicles demonstrated significant ATPase activity sensitive to N,N'-dicyclohexylcarbodiimide. The 10-20 μM PH2I did not affect the ATPase activity, whereas 40 μM PH2I caused a marked inhibition (~2 fold) in ATPase activity. The obtained results provide novel evidence on the involvement of hydrogenase and the F^sub 0^F^sub 1^-ATPase in H2 production by R. sphaeroides. Moreover, these data indicate the role of hydrogenase and the F^sub 0^F^sub 1^-ATPase in [increment]p generation. In addition, DMSO might increase an interaction of nitrogenase with CO2, decreasing nitrogenase activity and affecting H2 production.[PUBLICATION ABSTRACT]