What Biogeochemical Information Is Preserved in the Lipids of Extreme Archaea?

All life as we know it builds cell membranes that serve as an essential barrier from the external environment and facilitate the flow of matter and energy. The lipid membrane composition and its isotope composition may record information about the environment where it was synthesized, and these chemical signatures can be preserved in sediments over geologically relevant time scales. Of particular interest for astrobiology are microorganisms that thrive under extreme conditions. To understand what information can be preserved in the lipids of extremophilic archaea, we seek to construct interpretative frameworks for their lipid composition and isotope signatures in response to environmental conditions. In this talk, I will demonstrate metabolic and energetic considerations needed to interpret changes in archaeal lipid structures and hydrogen isotope compositions. First, the effect of carbon and energy metabolism on membrane cyclization was tested by cultivating the thermoacidophilic archaeon on different electron donor-acceptor pairs and carbon sources. We found that the patterns of membrane cyclization did not always align with thermodynamic predictions of energy yield; considering the kinetics of cellular energy metabolism provided a more comprehensive explanation for the observed lipid composition. Second, we conducted stable isotope probing experiments with a hyperthermophilic archaeon to test the effects of carbon metabolism and physiology on lipid-water isotope fractionation. The variation in isotope fractionation observed across tested conditions was relatively subtle, pointing to promising potential applications of archaeal lipid hydrogen isotope signatures as an environmental proxy. Together, our findings inform our interpretation of archaeal lipid compositions and isotope signatures in extreme environments, which provide useful insights for terrestrial analog studies in astrobiology and potential applications on extraterrestrial rocky bodies. 

Speaker: Jeemin Rhim (University of California, Santa Barbara)

Talks are held in the STScI John N. Bahcall Auditorium. Light lunch (provided) starts at 12pm; talk starts at 12:30pm.

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