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?

我们最近可以证明，除了Emden-Meyerhof-Parnas（EMP）和氧化戊糖磷酸（PNT）途径之外，蓝藻和植物都具有以前被忽视的第三种糖酵解途径：Entner-Doudoroff（艾德）途径（Chen et al. 2016，PNAS）。艾德途径的缺失导致在兼养（葡萄糖和光照）条件下和在暗/光循环（12小时暗/12小时光照）中生长减少。尽管这些观察表明艾德途径在蓝藻中具有生理重要性，但它并没有量化该途径的份额。因此，通量分析是绝对必要的，以发现其真正的贡献，中央碳代谢的蓝藻。阻断艾德和E2途径导致突变体在兼养和自养条件下生长极差（未发表）。这一结果令人惊讶，并清楚地表明，糖酵解途径是必不可少的自养条件下。由于其中一条糖酵解途径尚不清楚，因此目前对光合自养生物中糖酵解途径、碳固定和光合作用之间的相互作用研究还不够深入。该建议旨在量化所有糖酵解途径和Calvin-Benson-Bassham（CBB）循环下的CO2固定在兼养，异养和自养条件下的通量。我们的主要重点是研究糖酵解途径，碳固定和光合作用之间的相互联系。我们特别想验证这一假设，如果糖酵解途径是必不可少的补充CBB循环的CO2固定在光和它们是否需要平衡光合电子传递。对于这种方法的组合的通量分析，选定的缺失突变体和生理测量的表征是必要的。

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ED and OPP pathway results in a mutant with extremely poor growth under both mixotrophic and autotrophic conditions (unpublished).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.