Biomarker Insights Into Microbial Activity in the Serpentinite-Hosted Ecosystem of the Samail Ophiolite, Oman
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Astrobiology Science Conference 2015 (2015) 7536.pdf BIOMARKER INSIGHTS INTO MICROBIAL ACTIVITY IN THE SERPENTINITE-HOSTED ECOSYSTEM OF THE SAMAIL OPHIOLITE, OMAN. S. A. Newman1 and S. A. Lincoln1,2, E. L. Shock3, P. B. Kelemen4, R. E. Summons, 1Massachusetts Institute of Technology, Earth, Atmospheric and Planetary Sciences, Cambridge, Massachusetts 02139, 2Department of Geosciences, Penn State University, State College, PA 16801, 3Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287–1604, 4Lamont-Doherty Earth Observatory, Columbia University, 58 Geochemistry Building, Palisades, New York 10964 Serpentinization is an alteration process by which fatty acids) closely reflect those at Lost City [5,6], and ultramafic rocks react with water to produce hydrogen suggests the presence of similar microbial communities gas, serpentine (Mg3Si2O5(OH)4), and other minerals. at both sites [5]. During serpentinization, carbon dioxide is reduced to Modern serpentinite-hosted ecosystems are consid- methane and sulfate is reduced to hydrogen sulfide, ered to be possible analogs for early Earth and Mars which (along with hydrogen) can provide energy to (environments in which ultramafic and mafic rocks support chemosynthetic microbial activities once ser- were prevalent). Therefore, investigations into serpen- pentinizing fluids reach the surface or mix with more tinizing ecosystems not only inform us about modern oxidized groundwater [1,2]. microbial communities, but may also provide insight Here, we investigate the lipid biomarker record of into early life. microbial life from travertine and vein carbonates at [1] Sleep, N. H. et al. (2004) PNAS, 101, 12818– the Samail Ophiolite in the Sultanate of Oman, a site 12823. [2] Russell, M. J. et al. (2010) Geobiology, 8, undergoing active serpentinization [3]. The ophiolite, 355–71. [3] Barnes, I., O’Neil, J. R. (1978) GCA, 42, which formed 95-97 million years ago, was eventually 144-145. [4] Mervine, E. et al. (2014) GCA, 126, 371- emplaced onto the Arabian continental margin during 397. [5] Bradley, A. S., et al. (2009) GCA, 73, 102– the closure of the southern Tethys Ocean (70 Ma). Sta- 118. [6] Lincoln, S. et al. (2013) Organic Chemistry, ble carbon and oxygen isotopic analyses as well as 13C 60, 45-53. dating reveal travertine formation at Oman to have occurred over the past 50,000 years [4]. Our analyses of the carbonate samples reveal the presence of ether lipids (including glycerol dialkyl glycerol tetraethers, [GDGTs] and monoethers), as well as fatty acids. GDGTs present in our samples include those with 0-3 cyclopentane moieties (iGDGTs I-III) and crenarchaeol, an iGDGT containing 4 cyclopen- tane moieties and 1 cyclohexane moiety. Branched GDGTs (brGDGTS I-III) were also present in the car- bonate samples. Additionally, saturated and unsaturat- ed C14-C18 nonisoprenoidal monoether lipids and fatty acids were present in all samples. Crenarchaeol, a biomarker for autotrophic thaumar- chaea, provides a record of microbial carbon fixation in ophiolite veins. Monoethers and fatty acids suggest the presence of sulfate reducing bacteria at the site. In an effort to better understand the record of mi- crobial activity at Oman, we compare our study site to a similar serpentinite-hosted ecosystem, the Lost City Hydrothermal Field, an off-axis vent system near the mid-Atlantic ridge. Lost City is one of the best studied serpentinizing systems and DNA evidence from Lost City has revealed a diverse microbial community there, consistent with lipid biomarker evidence [5,6]. The suite of biomarkers found at the Semail ophiolite (iGDGTs 0-5, brGDGTs, isoprenoidal monoethers, and .