title: Modulation of the major paths of carbon in photorespiratory mutants of synechocystis.
abstract: BACKGROUND
  Recent studies using transcript and metabolite profiles of wild-type and gene deletion mutants revealed that photorespiratory pathways are essential for the growth of Synechocystis sp. PCC 6803 under atmospheric conditions. Pool size changes of primary metabolites, such as glycine and glycolate, indicated a link to photorespiration.
  
  
  RESULTS
  The (13)C labelling kinetics of primary metabolites were analysed in photoautotrophically grown cultures of Synechocystis sp. PCC 6803 by gas chromatography-mass spectrometry (GC-MS) to demonstrate the link with photorespiration. Cells pre-acclimated to high CO(2) (5%, HC) or limited CO(2) (0.035%, LC) conditions were pulse-labelled under very high (2% w/w) (13)C-NaHCO(3) (VHC) conditions followed by treatment with ambient (12)C at HC and LC conditions, respectively. The (13)C enrichment, relative changes in pool size, and (13)C flux of selected metabolites were evaluated. We demonstrate two major paths of CO(2) assimilation via Rubisco in Synechocystis, i.e., from 3PGA via PEP to aspartate, malate and citrate or, to a lesser extent, from 3PGA via glucose-6-phosphate to sucrose. The results reveal evidence of carbon channelling from 3PGA to the PEP pool. Furthermore, (13)C labelling of glycolate was observed under conditions thought to suppress photorespiration. Using the glycolate-accumulating ΔglcD1 mutant, we demonstrate enhanced (13)C partitioning into the glycolate pool under conditions favouring photorespiration and enhanced (13)C partitioning into the glycine pool of the glycine-accumulating ΔgcvT mutant. Under LC conditions, the photorespiratory mutants ΔglcD1 and ΔgcvT showed enhanced activity of the additional carbon-fixing PEP carboxylase pathway.
  
  
  CONCLUSIONS
  With our approach of non-steady-state (13)C labelling and analysis of metabolite pool sizes with respective (13)C enrichments, we identify the use and modulation of major pathways of carbon assimilation in Synechocystis in the presence of high and low inorganic carbon supplies.
authors.affiliation: Department of Physiology and Cell Biology, Leibniz Institute of Plant Genetics and Crop Plant Research, Gatersleben, Germany.
authors.forename: Jan
authors.initials: J
authors.lastname: Huege
authors.forename: Jan
authors.initials: J
authors.lastname: Goetze
authors.forename: Doreen
authors.initials: D
authors.lastname: Schwarz
authors.forename: Hermann
authors.initials: H
authors.lastname: Bauwe
authors.forename: Martin
authors.initials: M
authors.lastname: Hagemann
authors.forename: Joachim
authors.initials: J
authors.lastname: Kopka
mesh_terms: D002244:Carbon / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism; D002247:Carbon Isotopes / Q000378:metabolism; D004579:Electron Transport / Q000235:genetics*; D006016:Glycolates / Q000378:metabolism; D053858:Metabolic Networks and Pathways / Q000235:genetics*; D010788:Photosynthesis / Q000235:genetics*; D046939:Synechocystis / Q000235:genetics / Q000378:metabolism*
chemical_list: D002247:Carbon Isotopes; D006016:Glycolates; D002245:Carbon Dioxide; D002244:Carbon