Dissertation defence (Molecular Plant Biology): MSc Michal Hubácek
MSc Michal Hubácek defends the dissertation in Molecular Plant Biology titled “Towards Solar Chemicals: Understanding and Redesigning Photosynthesis” at the University of Turku on 15 August 2025 at 12.00 (University of Turku, Arcanum, Aava Auditorium, Arcanuminkuja 1, Turku).
Opponent: Professor Luning Liu (University of Liverpool, UK)
Custos: Professor Yagut Allahverdiyeva-Rinne (University of Turku)
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Tiivistelmä väitöstutkimuksesta / Summary of the Doctoral Dissertation:
Cyanobacteria are unicellular aquatic bacteria forming the base of the aquatic food chain. Alongside eukaryotic algae, they are responsible for half of the Earth’s oxygen production. This is thanks to the photosynthetic reactions that split water into electrons and oxygen, and fix atmospheric CO2 into biomass. Besides their ecological importance, they are emerging players in sustainable biotechnological applications. These range from pharmaceutical and supplement industries to food and feed production. Recently, they have found a role as biocatalysts in the production of solar chemicals.
This dissertation aims to deepen our understanding of the regulation of a major photoprotective mechanism, flavodiiron proteins (FDPs), their electron donors, and activity modulation. I show that ferredoxin, a crucial electron distribution hub in photosynthetic organisms, is the main electron donor to FDPs, and that their activity is dependent on the dynamic changes in cytosolic pH. In the second part of this work, I focus on characterising the physiological response of Synechocystis sp. PCC 6803 to its use as a biocatalyst in whole-cell biotransformation. A strong heterologous enzyme can consume high amounts of NADPH, the cellular electron carrier, outcompeting native photoprotective mechanisms and oxidising the photosynthetic electron transport chain. Additionally, I attempt to enhance the activity of whole-cell biotransformation by increasing the supply of NADPH via sugar metabolism or by modulating environmental conditions. While successful, the results also uncovered the complexity of whole-cell biotransformation, as different enzymes and strains respond differently.
These findings expand our knowledge of the regulation of photosynthesis and protective mechanisms, and shine light on the physiological response of cyanobacteria to whole-cell biotransformation applications. They propose directions for the future development of solar chemicals.
Opponent: Professor Luning Liu (University of Liverpool, UK)
Custos: Professor Yagut Allahverdiyeva-Rinne (University of Turku)
***
Tiivistelmä väitöstutkimuksesta / Summary of the Doctoral Dissertation:
Cyanobacteria are unicellular aquatic bacteria forming the base of the aquatic food chain. Alongside eukaryotic algae, they are responsible for half of the Earth’s oxygen production. This is thanks to the photosynthetic reactions that split water into electrons and oxygen, and fix atmospheric CO2 into biomass. Besides their ecological importance, they are emerging players in sustainable biotechnological applications. These range from pharmaceutical and supplement industries to food and feed production. Recently, they have found a role as biocatalysts in the production of solar chemicals.
This dissertation aims to deepen our understanding of the regulation of a major photoprotective mechanism, flavodiiron proteins (FDPs), their electron donors, and activity modulation. I show that ferredoxin, a crucial electron distribution hub in photosynthetic organisms, is the main electron donor to FDPs, and that their activity is dependent on the dynamic changes in cytosolic pH. In the second part of this work, I focus on characterising the physiological response of Synechocystis sp. PCC 6803 to its use as a biocatalyst in whole-cell biotransformation. A strong heterologous enzyme can consume high amounts of NADPH, the cellular electron carrier, outcompeting native photoprotective mechanisms and oxidising the photosynthetic electron transport chain. Additionally, I attempt to enhance the activity of whole-cell biotransformation by increasing the supply of NADPH via sugar metabolism or by modulating environmental conditions. While successful, the results also uncovered the complexity of whole-cell biotransformation, as different enzymes and strains respond differently.
These findings expand our knowledge of the regulation of photosynthesis and protective mechanisms, and shine light on the physiological response of cyanobacteria to whole-cell biotransformation applications. They propose directions for the future development of solar chemicals.
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