Pyruvate fermentation in light-grown cells of Rhodospirillum rubrum during adaptation to anaerobic dark conditions.

Pyruvate fermentation in Rhodospirillum rubrum (strains F1, S1, and Ha) was investigated using cells precultured on different substrates anaerobically in the light and than transferred to anaerobic dark conditions. Pyruvate formate lyase was always the key enzyme in pyruvate fermentation but its activity was lower than in cells which have been precultured aerobically in darkness. The preculture substrate also had a clear influence on the pyruvate formate lyase activity. Strains F1 and S1 metabolized the produced formate further to H2 and CO2. A slight production of CO2 from pyruvate, without additional H2-production, could also be detected. It was concluded from this that under anaerobic dark conditions a pyruvate dehydrogenase was also functioning. On inhibition of pyruvate formate lyase the main part of pyruvate breakdown was taken over by pyruvate dehydrogenase. When enzyme synthesis was inhibited by chloramphenicol, propionate production in contrast to formate production was not affected. Protein synthesis was not significant during anaerobic dark culture. Bacteriochlorophyll, however, showed, after a lag phase, a clear rise.