Influence of inorganic carbon and mutations in carbon-regulated pathways on metabolite pools and turnover in cyanobacteria

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The general scheme of basic carbon metabolism in photoautotrophic cells is known since decades. However, finished genome sequencing projects revealed that enzymes of key pathways are missing or such pathways seem to be variable organized in different organisms. Only scarcely investigated is the flux of metabolites through the network of interacting and competing pathways. Using the cyanobacterial strain Synechocystis sp. PCC 6803 as a simple model we want to analyze the carbon flow in a photosynthetic organism without compartmentation. The main tool of functional analysis will be metabolome studies of changes in metabolite pools size and stable isotope tracer studies utilizing GC-TOF-MS based metabolite profiling platform. The organism will be cultivated at different carbon levels and mutants showing defects in key pathways will be included. Particularly interesting will be the analysis of putative photorespiratory mutants, a pathway closely linked to photosynthesis but not well understood in its role especially in cyanobacteria. The main function of the photorespiratory cycle seems to be the conversion of 2-phophoglycolate to 3- phosphoglycerate and was found to be essential for plants at ambient CO2 concentration. In contrast, in cyanobacteria mutants in corresponding genes were found to be viable, which indicates that compensating pathways exist. The metabolome analyses will give hints, which pathways may be involved. Such results will improve our knowledge of photoautotrophic carbon metabolism and may be used to optimize plant photosynthesis in the future.