PhD Defense by Eftychia Symeonidou

PhD Thesis: Link for the PhD Thesis will be updated, when it is uploaded by the NBI-Education team - PhD theses - Astrophysics – Niels Bohr Institute - University of Copenhagen

Title: Life in the Extremities

Abstract: Billions of years divide the start of the universe until the present day. Multiple events led to the cosmos as we know it and equal seems to be the amount of the questions about them and which chain of events led to our existence on Earth. Some of these questions concern the presence of life in other parts of the universe and whether terrestrial life could survive outside our planet. Αstrobiology aims to answer some of those questions and the present thesis aspires to contribute to this scientific domain’s knowledge.

The thesis is divided in three main parts consisting of four studies. In the first part, we study the resilience of two microorganisms on Mars related conditions. The first study monitors a fungus isolate belonging to the species Penicillium chrysogenum. This fungus was found to persist in high salinity and interestingly in the presence of perchlorate salts which have also been detected in the martian surface. To understand the underlying mechanisms that enable that fungus to persist in those conditions we employ transcriptomics analysis techniques. Our results indicate that multiple and diverse mechanisms contribute to this characteristic of the fungus. The second studied microorganism, for the first part of this thesis, is the extremophile bacterium Deinococcus radiodurans which has been exposed to water freezing temperature and different perchlorate and chloride salts. The bacterium was exposed to the previous conditions for 30 days and its survival and metabolic activity were monitored and assessed. The acquired results show decreased activity at low temperature and as the concentration of the salt increased while survival decreased also along with salt concentration increase.

The second part focuses on the ability of a plant community to persist in full isolation. The inspiration and data for this work comes from the Tropical rainforest biome of the Bio-sphere 2 project. The evolution of the bio-community is studied under the prism of the Unified Neutral Theory of Biodiversity. In our models we predict a quick initial species loss which is decelerated in later stages until only one species prevails. The timescales predicted by the model differ greatly from the actual experimental results and for proper testing the duration of the actual experiment should have been at least 30 times longer. This study can give insight to microcosm and mesocosm study design and further on onboard and exoplanetary ecosystems. The last part of this thesis describes the process of comparing temperature-gas pressure profiles produced with the original MARCS code for stellar atmospheres and the newer MSG code that produces models substellar and exoplanetary atmospheres. Our results show consistency between the codes when models were computed for temperatures varying between 2500-3000K. The longterm perspective of this study is to make it possible to study the influence of biological metabolism on the emerging spectra of Earth-like exoplanets. Overall, this thesis has employs interdisciplinary knowledge of physics and biology to address different astrobiology related questions.

Supervisor:

  • Uffe Gråe Jørgensen, Niels Bohr Institute, University of Copenhagen

Co-Supervisor:

  • Anders Priemé, Niels Bohr Institute, University of Copenhagen

PhD Evaluation Committee:

  • Dirk Schulze-Makuch, Technische Universität Berlin (TU Berlin)
  • Kai Finster, Department of Biology - Microbiology, Aarhus University
  • Namiko Mitarai, Niels Bohr Institute, University of Copenhagen

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There will be a following reception in either the “Inge Lehmann Atrium” across the Margrethe Bohr Aud. or in front of the Aud. A. at Microbiology.