Regulation der Photosynthese für die Stickstoff-Fixierung in Trichodesmium

丝状蓝藻Trichodesum在光照期间进行光合作用和固氮，而不需要特化细胞的分化。它通过不同活性状态之间的可逆转换来实现这一点，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Diel的活性模式主要与现有色素-蛋白质复合体的可逆生化或生物物理修饰有关，特别是藻胆体的差异(非)偶联。通过铁限制来探索这一调控并不会导致需要PS I的铁和需要藻胆的氮的下调，但会导致固氮酶的选择性下调，以及捕光复合体的变化，比如表达不同的藻红蛋白亚型。现在，我们想要更详细地定量地剖析藻胆体的可逆(非)偶联，分离和表征藻红蛋白的新亚型。此外，我们想要研究在体内活动周期和铁限制压力下发现的类胡萝卜素变化的生理学意义。在体内，UV/VIS荧光和吸收动力学的空间和光谱分辨显微测量将得到补充，例如蛋白质层析、固氮酶活性测量和Western blotts。

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.