DRAFT
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Geology Club Seminar

Thursday, March 21, 2019
4:00pm to 5:00pm
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Arms 151 (Buwalda Room)
Combining Deep UV Raman spectroscopy and stable isotope probing to map microbial activity on complex environmental substrates: from life detection to the subsurface biosphere
Haley Sapers, Postdoc, Division of Geologic and Planetary Sciences, California Institute of Technology,

Understanding the interactions between microorganisms and their substrates requires knowledge of the community structure and assessment of the spatial distribution of metabolic activity. The challenges associated with identifying cells in the subsurface has parallels to those faced by life detection missions on other planetary bodies. Here we demonstrate a novel technique combining stable isotope probing (SIP) and Deep UV (DUV) Raman spectroscopy as a means to trace microbial metabolic activity on complex environmental substrates. First, we show that DUV Raman spectroscopy can differentiate an organic signal from a definitively biological one as a result of the unique molecular complexity inherent to living organisms. Second, using SIP we show that DUV Raman spectroscopy can differentiate bacterial cells grown in isotopically labeled media on environmental substrates based on downshifting of characteristic Raman peaks. Finally, a combined DUV Raman-SIP approach has the potential to identify microbial activity while obtaining the spatial community structure relative to the environmental substrate through correlated DUV fluorescence spectroscopy mapping. In situ field incubations of mineral substrates in a deep continental setting illustrate the ability of scanning DUV fluorescence to localize and visualize biomass on environmental substrates. The ability of DUV Raman to effectively identify regions containing cells that have incorporated isotopic labels combined with targeted fluorescence mapping will facilitate in situ detection of active community members on natural mineral substrates, providing a crucial link between microbial activity and environmental context. The ability to differentiate organic matter from cellular material is a critical step for life detection and fundamental to biosignature detection for both assessing microbial colonization in the deep subsurface and the search for life on other potentially habitable worlds such as Mars.