PhD Defence: Elena Carrasquer-Álvarez
Title: Going greener: Exploring cyanobacterial carbon capture at inhibitory high CO2 concentrations
Supervisor: Assoc. Prof. Niels-Ulrik Frigaard Department of Biology, University of Copenhagen
Co-supervisor: Prof. Brian Frederick Pfleger Department of Chemical and Biological Engineering, University of Wisconsin-Madison, USA
Assessment committee:
Prof. Per Juel Hansen – CHAIRMAN Department of Biology, University of Copenhagen
Assoc. Prof. Michele Fabris Department of Green Technology, University of Southern Denmark, Odense
Prof. Yagut Allahverdiyeva-Rinne Department of Life Technologies, University of Turku, Finland
Abstract:
This PhD thesis investigates the use of photosynthetic microbes, specifically cyanobacteria, to capture CO2 from waste streams that have high contents of CO2, addressing the urgent need to limit the anthropogenic release of CO2. The research focused on two model cyanobacteria: the marine Synechococcus sp. PCC 7002 and the freshwater Synechocystis sp. PCC 6803. A novel medium was developed to cultivate these strains at CO2 levels as high as 30% without altering the pH, allowing for detailed analysis of the organisms’ responses to high concentrations of CO2 and bicarbonate. The study suggests that growth inhibition in these cyanobacteria is due to CO2 and not bicarbonate and that this inhibition is light dependent. RNA sequencing provided insights into the transcriptional changes under high CO2, revealing that photosynthesis and stress responses are regulated, although not optimally. Genetic analyses using single and double mutants highlighted the importance of inorganic carbon transport regulation and pH homeostasis. Additionally, a CRISPRi library was used to identify genes involved in growth inhibition under high CO2, revealing roles for specific light-harvesting antennas and electron transfer mechanisms. These comprehensive analyses enhance our understanding of CO2 capture by photosynthetic microorganisms and paves the way for future basic research and potential biotechnological applications.
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