Microbiology, Vol 145, 1743-1748, Copyright © 1999 by Society for General Microbiology
Evidence for the presence of the reductive pentose phosphate cycle in a filamentous anoxygenic photosynthetic bacterium, Oscillochloris trichoides strain DG-6
RN Ivanovsky, YI Fal, IA Berg, NV Ugolkova, EN Krasilnikova, OI Keppen, LM Zakharchuc and AM Zyakun
Department of Microbiology, Moscow State University, Moscow, 119899, Russia
Studies on autotrophic CO(2) fixation by the filamentous anoxygenic
photosynthetic bacterium Oscillochloris trichoides strain DG-6 demonstrated
that, unlike other green bacteria, this organism metabolized CO(2) 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-bisphosphate-dependent CO(2) 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(2) assimilation by whole
cells as well as by cell extracts of O. trichoides. The (13)C/(12)C carbon
isotope fractionation during photoautotrophic growth of O. trichoides was
-19.7(o)/(oo), which is close to that obtained for autotrophic organisms
that use ribulose-1,5-bisphosphate carboxylase as the primary carboxylation
enzyme. Cell extracts of O. 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 O. trichoides DG-6.
