How do glycolytic routes and especially the newly discovered Entner-Doudoroff pathway contribute to the central carbon metabolism in cyanobacteria and do they play an essential role for carbon fixation and photosynthesis?

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We could recently show that both cyanobacteria and plants possess a previously overlooked third glycolytic route beside Emden-Meyerhof-Parnas (EMP) and oxidative pentose phosphate (OPP) pathway: the Entner-Doudoroff (ED) pathway (Chen et al. 2016, PNAS). Deletion of the ED pathway results in diminished growth both under mixotrophic (glucose and light) conditions and in a dark/light cycle (12h dark/12h light). Even though these observations indicate that the ED pathway is of physiological importance in cyanobacteria it does not quantify the share of this pathway. Therefore, flux analyses are absolutely essential to discover its true contribution to the central carbon metabolism in cyanobacteria. Interruption of both ED and OPP pathway results in a mutant with extremely poor growth under both mixotrophic and autotrophic conditions (unpublished). This result came as a surprise and clearly shows that glycolytic routes are essential under autotrophic conditions. The interplay between glycolytic routes, carbon fixation and photosynthesis could not be studied satisfactory in photoautotrophs until now, as one of the glycolytic routes was unknown. This proposal aims to quantify the fluxes through all glycolytic routes and the Calvin-Benson-Bassham (CBB) cycle of CO2 fixation under mixotrophic, heterotrophic and autotrophic conditions. Our main emphasis is to study the interconnection between glycolytic routes, carbon fixation and photosynthesis. We especially want to test the hypothesis, if glycolytic routes are essential to replenish the CBB cycle of CO2 fixation in the light and whether they are required to balance the photosynthetic electron transport. For this approach a combination of flux analyses, characterization of selected deletion mutants and physiological measurements are needed.