Regulation der Photosynthese für die Stickstoff-Fixierung in Trichodesmium

丝状蓝细菌束毛藻在光照期间进行光合作用和固氮，而不分化专门的细胞。它通过不同活性状态之间的可逆转换来实现，包括无氧PSII介导的光合作用（通过Mehler反应）。本项目研究调节光合作用固氮的生理机制。我们发现，昼夜活动模式主要与现有的色素-蛋白质复合物的可逆的生物化学或生物物理修饰，特别是藻胆体的差异（不）耦合。探测这种调节铁限制并没有导致铁需要PS I和氮需要藻胆体的下调，但引起固氮酶的选择性下调，并在捕光复合物的变化，如藻红蛋白的不同亚型的表达。现在，我们想定量解剖的可逆（解）耦合藻胆体更详细，分离和表征的新异构体的藻红蛋白。此外，我们想调查的生理重要性的类胡萝卜素的变化，发现在昼夜活动周期和铁限制压力。体内空间和光谱分辨的UV/维斯荧光和吸收动力学显微镜测量将通过蛋白质色谱法、固氮酶活性测量和蛋白质印迹法等进行补充。

The filamentous cyanobacterium Trichodesmium carries out photosynthesis and nitrogen fixation during the light period without differentiation of specialised cells. It does so via reversible switching between different activity states including anoxygenic PSII-mediated photosynthesis (via Mehler reaction). This project investigates the physiological mechanisms that regulate photosynthesis for nitrogen fixation. We found that the diel activity pattern is primarily related to reversible biochemical or biophysical modifications of existing pigment-protein complexes, in particular differential (un)coupling of phycobilisomes. Probing this regulation by iron limitation did not lead to downregulation of Fe requiring PS I and nitrogen requiring phycobilisomes, but caused selective downregulation of nitrogenase, and changes in light harvesting complexes like expression of a different isoform of phycoerythrin. Now we want to quantitatively dissect the reversible (un)coupling of phycobilisomes in more detail, isolate and characterisation of the new isoform of phycoerythrin. Additionally, we would like to investigate the physiological importance of the changes in carotenoids that were found in the diel activity cycle and under iron limitation stress. In vivo spatially and spectrally resolved microscopic measurements of UV/VIS fluorescence&absorption kinetics will be supplemented e.g. by protein chromatography, nitrogenase activity measurements and Western blots.