No abstract

Studies on autotrophic CO, fixation by the filamentous anoxygenic photosynthetic bacteri um Oscillochloris frichoides strain DG-6 demonstrated that, unlike other green bacteria, this organism metabolized CO, via the reductive pentose phosphate cycle. Both key enzymes of this cycle -ribulose-1,5-bisphosphate carboxylase/oxygenase and phosphoribulokinase -were detected in cell extracts. The main product of ribulose 1,5-bisphosphatedependent CO, fixation was 3-phosphoglyceric acid. KCN, which is known to be a competitive inhibitor of ribulose-1,5-bisphosphate carboxylase/oxygenase, completely inhibited the CO, assimilation by whole cells as well as by cell extracts of 0. frichoides. The I3Ul2C carbon isotope fractionation during photoautotrophic growth of 0. trichoides was -19*7O/io, which is close to that obtained for autotrophic organisms that use ribulose-1,5-bisphosphate carboxylase as the primary carboxylation enzyme. Cell extracts of 0. trichoides contained all the enzymes of the tricarboxylic acid cycle except 2-oxoglutarate dehydrogenase. No activity of isocitrate lyase, a key enzyme of the glyoxylate shunt, was found in cell extracts of 0. frichoides DG-6.