Pyruvate fermentation in light-grown cells ofRhodospirillum rubrum during adaptation to anaerobic dark conditions

Abstract

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.

Effect of pyruvate on the metabolic regulation of nitrogenase activity in Rhodospirillum rubrum in darkness

“…The Pfl pathway has been established as the main pathway for utilization of pyruvate as a carbon source in dark anaerobic R. rubrum cultures (Gorrell & Uffen, 1977; Voelskow & Schön, 1978). The first reaction in this pathway is catalysed by Pfl, the conversion of pyruvate to acetyl-CoA and formate (Becker & Kabsch, 2002).…”

“…We could also not detect any new proteins by 2D-PAGE at the time of appearance of nitrogenase activity after addition of pyruvate (data not shown). Very little is known about the regulation of the Pfl pathway in R. rubrum apart from the fact that no or little Pfl activity can be detected in phototrophically grown cultures (Voelskow & Schön, 1978).…”

“…Using pyruvate as a carbon source, R. rubrum can grow both anaerobically in the light and aerobically or anaerobically in the dark. Under dark anaerobic conditions, R. rubrum utilizes pyruvate mainly through the pathway in which pyruvate formate-lyase (Pfl) catalyses the first reaction, to generate the ATP necessary for growth (Gorrell & Uffen, 1977; Jungermann & Schön, 1974; Voelskow & Schön, 1978). Pfl has been extensively studied in other organisms, such as Escherichia coli and Lactococcus lactis (Becker & Kabsch, 2002; Lehtiö et al , 2002; Melchiorsen et al , 2000; Rasmussen et al , 1991; Sawers & Suppmann, 1992) and was shown to be induced by anaerobic conditions in E. coli (Rasmussen et al , 1991; Sawers & Suppmann, 1992).…”

Propionate formation in Rhodospirillum rubrum under anaerobic dark conditions

“…Thus in fermentation metabolism with pyruvate as substrate propionate formation is probably without much importance, as no net ATP production occurs. Furthermore, under good fermentative conditions pyruvate is normally broken down to acetyl-CoA and formate, then formate is split further to CO, and H, by most strains of R. rubrum, so that excess reducing equivalents are eliminated as H, (SCIION and VOELSKOW 1976, VOELSKOW and SCHON 1978, 1980. It is interesting that on exhaustion of pyruvate in the medium the propionyl-CoA carboxylase rises as the breakdown of endogenous reserves begins.…”

“…2 drops silicon-antifoam (1 : 1000 diluted, RoTH-Karlsruhe) were then added and air streamed for 30 min through the solution to eliminate all unfixed 14C02. The incorporated 14C0, was measured in the same vials after addition of 18 ml Triton-toluene scintillation mixture (VOELSKOW and SCHON 1978). The quench correction was determined by the automatic external standard (A.E.S.…”