Dynamic organization of glycolytic routes and the Calvin-Benson-Bassham cycle during the autotrophy-heterotrophy switch

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Processes that operate in opposite directions are highly intertwined in the central carbohydrate metabolism of the cyanobacterium Synechocystis sp. PCC 6803. Glycolytic routes, that metabolize carbohydrates in catabolic direction, share several enzymes and reactions with the Calvin-Benson-Bassham (CBB) cycle, which operates anabolically. These opposing processes are not separated spatially, as cyanobacteria are prokaryotes without any further compartmentation. As the fixation of CO2 via the CBB cycle is driven by photosynthesis in the light, whereas glycolytic routes are of importance for the catabolic utilization of carbohydrates in darkness, both processes are separated time-wise during the autotrophy heterotrophy switch between light and darkness. However, together with our cooperation partners Forchhammer and Wittmann, we could show that glycolytic routes are as well of importance under autotrophic conditions. They form shunts in transition states that replenish and fine-tune the CBB cycle. For this, internal glycogen reservoirs are utilized as carbohydrate sources. Key enzymes of the Enter-Doudoroff (ED) pathway and the oxidative pentose phosphat (OPP) pathway participate in these shunts whereas the Emden-Meyerhoff-Parnas (EMP) pathway is not involved. We plan to investigate the fine-tuning of glycolytic routes und the CBB cycle further and to examine particularly, if these processes show a dynamic organization on a spatial level in the cells. Apart from that, the physiologic characterization of a mutant (Δeda) with deleted ED pathway together with our cooperation partners Hagemann and Forchhammer revealed several phenotypic differences in comparison to the wild type (WT). These findings are partly contradictory to flux analyses. We therefore plan to check, if the observed phenotypes of Δeda rely exclusively on the deletion of Eda, or whether other regulatory units as e.g. noncoding RNAs were silenced during the construction of the mutant which might be responsible for the observed differences to the WT. In addition, we want to check if Eda might have moonlight functions or might participate in dynamic processes for the fine-tuning of the central carbohydrate metabolism