Abstract
The effect of trace elements (Fe, Ni) and chelating compounds on the activity of hydrogen (H2) uptake (Hup) hydrogenase, nitrogenase and rate and yield of H2 photoproduction from l-lactate in photosynthetic cultures of Rhodospirillum rubrum was investigated. Hup activity depended on the availability of Ni2+ and was inhibited by EDTA (0.3–0.5 mm ethylenedinitrilotetraacetic acid). Addition of EDTA (0.5 mm) to the culture medium caused a nearly complete inactivation of Hup activity and activation of nitrogenase, which was paralleled by a threefold increase in total H2 photoproduced from lactate. Hup− mutants, isolated by transposon Tn5 mutagenesis, produced maximally twofold more H2 than the wild-type. Experiments with different chelating agents [EDTA, NTA (nitrilotriacetic acid), citrate, isocitrate] and varying concentrations of Fe2+ and Fe3+ showed that photosynthetic growth and nitrogenase activity of R. rubrum were strongly influenced by the iron supply. It is concluded that EDTA enhanced H2 photoproduction by (I) inhibition of biosynthesis of Hup hydrogenase and (II) mobilization of iron, thereby activating the biosynthesis of the nitrogenase complex.
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