The role of Bacteria in the atmosphere and their potential as Biosignatures on Exoplanets.

PhD defence, Friday 31 March 2017. MeiLee Ling.

2017.03.31 | Steffi Hjerrild Iversen

Mei Lee Ling

Ice dendrites pattern during ice crystal growth in the bacteria ice nucleation active protein solution.

Microorganisms have been proposed to play a role in shaping the Earth’s weather patterns and climate by inducing ice formation in the atmosphere, which influences the formation of clouds and precipitation. During her PhD studies, MeiLee Ling investigated the ice nucleation active proteins (INA proteins) of an ice nucleation active bacterium - Pseudomonas syringae, using DNA recombination, immuno-staining, flow-cytometry and electron microscopy. The findings of her structural and functional studies of the purified recombinant INA protein are fundamental for our understanding of the proteins role in the freezing process and ultimately how it could influence cloud and rain formation. Her research has demonstrated that the cell-free, nano-size INA protein is still capable to form ice at much higher temperatures than dust and mineral particles, which are the numerically most important ice-nuclei in Earth atmosphere.

MeiLee Ling has additionally investigated how and under which conditions this bacterium expresses the gene (ina) that codes for the ice nucleation active protein by analyzing the bacterial genome and by studying the expression of ina gene in single bacterial cells using Fluorescence-Activated Cell Sorting (FACS) and live cell microscopy. This can help in advancing our knowledge of the fundamental molecular principles regulating the ina gene expression of the bacteria.

MeiLee Lings’ work has also implications for the search for life on exoplanets as this search is based on investigating the composition and the processes occurring in these planets atmospheres. The new insights into bacterial ice nucleation activity in the Earth’s atmosphere will contribute to developing techniques and models that will allow identifying the role microorganisms in cloud formation, which than can serve as a biosignature in exoplanet atmosphere studies and ultimately to investigate the existence of life on these planets.

The PhD degree was completed at the Section for Microbiology, Aarhus University.

This résumé was prepared by the PhD student.

Friday 31 March 2017 at 10:30
Place: Building 1523, Room 318, Department of Physics and Astronomy, Ny Munkegade 120, Aarhus University, 8000 Aarhus C.
Title of dissertation: Atmospheric Ice Nucelation Active Bacteria – Potential Biosignature on Exoplanet
Contact information:
MeiLee Ling, e-mail:
Members of the assessment committee:

Dr. Pierre Amato, French National Centre for Scientific Research (CNRS), France
Associate Professor Kim Præbel, Department of Marine and Arctic Biology, The Artctic University of Norway, Norway
Associate Professor Nils Risgaard-Petersen (chair), Department of Bioscience, Aarhus University
Main supervisor:
Professor Kai Finster, Department of Bioscience, Aarhus University
Associate Professor Thomas Boesen, Department of Molecular Biology and Genetics, Aarhus University
The PhD dissertation will be defended in English.

The defence is public.
The dissertation is available for reading at the Graduate School of Science and Technology/GSST, Ny Munkegade 120, building 1520, rooms 128-134, 8000 Aarhus C.

PhD defence
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Revised 17.05.2018