Dissertation Defense

The Tree of Life aims to map evolutionary relationships underlying life's complexity. However, metagenomics is transforming our view of biodiversity, helping to resolve critical evolutionary branching points, particularly the origin of eukaryotes. This dissertation focuses on extracting and organizing over 10 Tb of sequencing data from hydrothermally influenced deep-sea sediments, uncovering a rich genomic catalog with more than 60 unclassified taxa. By integrating this new data with previous sequencing efforts, the public genomic database nearly doubled, allowing for a comprehensive analysis of Asgardarchaeota across diverse environments and unveiling key evolutionary transitions.

Asgardarchaeota (specifically Hodarchaeales) are proposed descendants of the archaeal host central to eukaryogenesis. The study revealed the involvement of two Asgardarchaeota lineages in wetland carbon cycling and their potential to transfer cellular complexity via mobile genetic elements. Furthermore, analysis of Hodarchaeales demonstrated oxygen tolerance and possible aerobic respiration, challenging conventional views on the conditions that facilitated the emergence of eukaryotes. This expanded genomic catalog and its detailed comparative analyses offer an invaluable resource for studying deep-sea life and understanding the evolution of cellular complexity.