PhD Defence: Miguel Angel Salinas García

Thesis title: Astrobiological exploration of Northern Greenland and its microbial volatile biosignatures

Supervisor:  Anders Priemé

Assessment committee
Professor Mette Burmølle (chair), Department of Biology, University of Copenhagen
Senior scientist and research group leader Paolina Garbeva, Department of Microbial Ecology, The Netherlands Institute of Ecology
Professor Kai Finster, Department of Biology, Aarhus University

Abstract
Astrobiology is the field of science dedicated to the study of origin of life on Earth and the existence of life elsewhere in the universe. To detect life beyond Earth, astrobiologists investigate biosignatures: chemical, physical or molecular markers that indicate past or present life. Identifying robust biosignatures requires understanding the environmental contexts in which they form, which is where terrestrial analogues play a vital role. These Earth environments mimic the extreme conditions found on other planets and moons, allowing esearchers to study life forms that endure extreme temperatures, pH, radiation, pressure, and more. Studying life in these extreme environments enhances our understanding of the limits of life and aids in designing missions and instruments for further research. This thesis investigates bacterial isolates from Peary Land, and their production of Volatile Organic Compounds (VOCs) with potential as biosignatures. Peary Land is a peninsula in Northern Greenland characterised by a polar desert climate, exhibits low temperatures, nutrient-poor soils and scarce precipitation. These characteristics are similar to those of present and past Mars, making Peary Land a Mars analogue. Samples from three environments in Peary Land were used in this thesis: Citronen Fjord (biocrust), Cape Morris Jessup (biocrust and soil) and Kap København (permafrost soil). A total of 57 bacterial strains were isolated, including 17 with saline media. Genomic analysis of selected halotolerant isolates revealed adaptations to low temperatures and high salinity, including compatible solute synthesis and uptake, cold shock proteins, and genes related to membrane fluidity. In addition, the genomes were found to contain several biosynthetic gene clusters. The phylogeny and physiology of two of these strains was explored in detail, revealing that they represent two novel bacterial species. To assess the potential of VOCs as biosignatures, a thorough literature review on the diversity of VOCs in extreme environments was performed. Furthermore, the VOC emission of three selected Peary Land strains across a salt gradient was investigated. We found that salt has a significant effect on both quantity and quality of emitted VOCs and that, throughout bacterial growth, unique VOC emissions patterns occur. The results presented in this thesis show that Peary Land hosts a diverse array of extremophiles that offer valuable insights into adaptations to low temperatures and high salinity, with applications in astrobiology. Furthermore, the unique VOC patterns presented here may serve as robust biosignatures in future missions and observations. Beyond astrobiology, this thesis highlights the bioprospection potential of Peary Land microbes as producers of bioactive compounds, with implications in biotechnology, and underscores the potential ecological role of VOCs in nitrogen and sulphur cycling in these remote environments, especially in the context of climate change.