Novel lipid biomarkers for detecting microbial oxidation of methane in the environment

Methane is a powerful greenhouse gas which has impacted Earth´s climate for millions of years. Some of the naturally and anthropogenically emitted methane is, however, oxidized to CO₂ by microbes before reaching the atmosphere. To trace microbes in past environments, we mostly rely on fossilized molecules, called biomarker lipids. However, to this date, only a few unambiguous biomarkers for methane-oxidizing bacteria are known. In this thesis, microbial cultures and environmental samples from terrestrial methane seeps in Sicily (Italy) were investigated for unambiguous biomarkers of these bacteria. We identified various novel lipid biomarkers that are indicative for certain methane-oxidizing bacteria, for example bacteriohopanepolyols. Using these lipid biomarkers, we were able to create a new tool which shows whether methane-oxidizing bacteria are abundant in environmental settings. Intriguingly, we discovered novel bacteria closely related to tuberculosis bacteria which had unique biomarkers and were oxidizing ethane, another greenhouse gas related to methane. In summary, the results of this thesis offer new lipid biomarkers to trace methane oxidizing microbes, especially in terrestrial environments. Therefore these new findings have substantially expanded the toolbox to study methane cycles in present and past environments in the future.