Paper No. 168-4
Presentation Time: 8:55 AM
A CASE STUDY ON MICROBIAL COMMUNITIES AND BIOSIGNATURE PRESERVATION IN ACIDIC CAVE GYPSUM
JONES, Daniel1, HAVLENA, Zoe E.2, GRAHAM, Heather V.3, STERN, Jennifer C.4, MAINIERO, Maurizio4, WEISS, Gabriella M.5, CHUNG, Angela H.6, MOJARRO, Angel3 and WANKEL, Scott D.7, (1)Earth and Environmental Science, New Mexico Institute of Mining and Technology, Socorro, NM 87801; National Cave and Karst Research Institute, Carlsbad, NM 88220, (2)Earth and Environmental Science, New Mexico Institute of Mining and Technology, Socorro, NM 87801, (3)NASA Goddard Space Flight Center, Astrobiology Analytical Laboratory, Code 691, Bldg 34, Room S139, Greenbelt, MD 20771, (4)Gruppo Speleologico Marchigiano, Ancona, Italy, (5)NASA Goddard Space Flight Center, Greenbelt, MD 20771; University of Maryland, College Park, MD 20742; NASA Goddard Space Flight Center, Center for Research and Exploration in Space Science and Technology II, Greenbelt, MD 20771, (6)NASA Goddard Space Flight Center, Astrobiology Analytical Laboratory, Code 691, Bldg 34, Room S139, Greenbelt, MD 20771; Catholic University of America, Washington, DC 20064, (7)Department of Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543
Gypsum (CaSO
4•2H2O) and other hydrated sulfate minerals are widespread on the surface of Mars, and these evaporite deposits are considered targets for the detection of past and present life. On Earth, gypsum primarily forms in evaporative settings, including in extremely acidic playas that are considered excellent analogues for Martian sediments. However, while acidic gypsum-precipitating environments on Earth often host diverse microbial communities, we don’t know how faithfully these sulfates preserve biosignatures.
In this study, we combined high-throughput rRNA gene sequencing, metagenomics, and cell counts with organic geochemical analyses to explore microbial colonization and molecular biosignature content of extremely acidic gypsum in the Frasassi cave system, Italy. The Frasassi Caves are an active sulfuric acid cave system in which secondary gypsum deposits form above the water table where biogenic sulfuric acid corrodes the host limestone. Gypsum deposits can persist for 100s of thousands to millions of years in sulfuric acid caves, and has the potential to trap organics from the chemolithotrophic microorganisms associated with gypsum formation. We found that freshly-formed gypsum surfaces were colonized by Acidithiobacillus spp. and Thermoplasmatales-group Archaea that, based on previous research and new metagenomic evidence, can produce bacteriohopanepolyols (BHPs) and glycerol dialkyl glycerol tetraethers (GDGTs), respectively. In older gypsum deposits further from the cave water table, these organisms decrease in abundance and are replaced by Alphaproteobacteria and other taxa not associated with fresh deposits. However, despite the active microbial communities, organic biomarker recovery has proven challenging, even from fresh gypsum. In this presentation, we will share results from amino acid and lipid analyses, as well as lessons learned in the search for diagnostic biomarkers in low biomass microbial communities from acidic, oxidizing mineral environments.
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