Pathway and Importance of Photorespiratory 2-Phosphoglycolate Metabolism in Cyanobacteria
Cyanobacteria invented oxygenic photosynthesis about 3.5 billion years ago. The by-product molecular oxygen initiated the oxygenase reaction of RubisCO, the main carboxylating enzyme in photosynthetic organisms. During oxygenase reaction, the toxic side product 2-phosphoglycolate (2-PG) is produced and must be quickly metabolized. Photorespiratory 2-PG metabolism is used for this purpose by higher plants. The existence of an active 2-PG metabolism in cyanobacteria has been the subject of controversy since these organisms have evolved an efficient carbon-concentrating mechanism (CCM), which should considerably reduce the oxygenase activity of RubisCO. Based on emerging cyanobacterial genomic information, we have found clear indications for the existence of many genes possibly involved in the photorespiratory 2-PG metabolism. Using a genetic approach with the model Synechocystis sp. strain PCC 6803, we generated and characterized defined mutants in these genes to verify their function. Our results show that cyanobacteria perform an active photorespiratory 2-PG metabolism, which employs three routes in Synechocystis: a plant-like cycle, a bacterial-like glycerate pathway, and a complete decarboxylation branch. In addition to the detoxification of 2-PG, this essential metabolism helps cyanobacterial cells acclimate to high light conditions.
KeywordsCyanobacterial Cell Oxygenic Photosynthesis Cyanobacterial Strain Glycolate Oxidase Cyanobacterial Genome
The authors would like to thank Dr. Aaron Kaplan, Hebrew University, Jerusalem, Israel, and Dr. Hans C. P. Matthijs, University of Amsterdam, Amsterdam, The Netherlands, for fruitful cooperation during the work on cyanobacterial photorespiration. This work was supported by grants from the DFG (Deutsche Forschungsgemeinschaft).
- Hackenberg C, Engelhardt A, Matthijs HCP et al (2009) Photorespiratory 2-phosphoglycolate metabolism and photoreduction of O2 cooperate in high-light acclimation of Synechocystis sp. strain PCC 6803. Planta, epub ahead of press, doi 10.1007/s00425-009-0972-9Google Scholar
- Kroth PG, Chiovitti A, Gruber A et al (2008) A model for carbohydrate metabolism in the diatom Phaeodactylum tricornutum deduced from comparative whole genome analysis. PLoS One 3:e1426Google Scholar
- Margulis L (1970) Origin of eukaryotic cells. Yale University Press, New Haven.Google Scholar
- Mereschkowsky C (1905) Über Natur und Ursprung der Chromatophoren im Pflanzenreiche. Biol Centralbl 25:593–604Google Scholar