Regulation der Photosynthese für die Stickstoff-Fixierung in Trichodesmium

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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.