Exploration of biosynthetic pathways involved in lipid biomarker biosynthesis in cyanobacteria and haptophyte algae

Biomarkers are important tools used in a wide range of scientific disciplines that can serve as measurable indicators of diverse processes and environmental parameters. In paleoclimatology and biogeochemistry, specific biomarkers allow us to study the presence of certain organisms and the occurrence of relevant geochemical processes throughout Earth’s history. The current period of rapid environmental change—characterized by increased atmospheric CO2, rising global temperatures, ocean acidification and eutrophication—is bringing us into uncharted territory. To better prepare for the future, we can look at the past, studying how ancient environments responded to sudden shifts in environmental conditions. Lipid biomarkers produced by microorganisms inhabiting marine and lacustrine environments are particularly valuable tools for paleoclimate reconstruction. They can be well preserved in the sediments and can reflect the conditions in which the source organisms lived. This thesis combines lipidomic and genomic approaches to investigate two such classes of lipid biomarkers; heterocyte glycolipids (HGs) and long-chain alkenones (LCAs), both produced by photosynthetic microorganisms inhabiting the photic zone of the water column. By examining their biosynthetic pathways, evolutionary history, and environmental sources, this work aims to refine our understanding of these lipids and their application in critical paleoproxies.