Growth and adaptive hydrogen production of Rhodospirillum rubrum (F1) in anaerobic dark cultures

Rhodospirillum rubrum (F₁) maintained electron balance mainly by producing propionate, formate and H₂ during fermentation metabolism. H₂ formation was inversely correlated with the production of propionate.In diluted, growing cultures high amounts of H₂ and only traces or no propionate were produced from pyruvate. In dense cultures or in resting cultures without (NH₄)₂SO₄, however, propionate was formed from pyruvate in relatively high amounts Cultures always produced much more propionate than H₂ from fructose in contrast to cells with pyruvate. Kinetic studies of growth and excretion of fermentation products indicated that the enzyme system for H₂ formation is adaptive. Chloramphenicol (3 μg/ml) completely inhibited the formation of H₂ if the cells were not adapted to fermentation metabolism. The production of propionate, on the other hand, was not prevented by chloramphenicol after shifting the cells from aerobic dark culture with malate to fermentation conditions with pyruvate.H₂ formation was not influenced by sodium ascorbate but it was significantly decreased by K₃Fe(CN)₆].Poly(β-hydroxybutyric acid) was also synthesized by the cells during anaerobic dark metabolism especially in dense cultures, probably favoured by the rapid acidification of the medium. Formate can also accumulate in the fermentation metabolism, especially in young growing cultures.These results give an explanation for the differing reports in the literature on the fermentation metabolism of R. rubrum.