HR: 0800h
AN: B41A-0031    [Abstracts]
TI: Lipid and Phylogenetic Analysis of a Gypsum-hosted Endoevaporitic Microbial Community
AU: * Turk, K A
EM: Kendra.A.Turk@nasa.gov
AF: SETI Institute, NASA Ames Research Center Mail Stop 239-4, Moffett Field, CA 94035, United States
AU: Jahnke, L L
EM: Linda.L.Jahnke@nasa.gov
AF: Exobiology Branch, NASA Ames Research Center Mail Stop 239-4, Moffett Field, CA 94035, United States
AU: Green, S J
EM: sjgreen@mail.arc.nasa.gov
AF: SETI Institute, NASA Ames Research Center Mail Stop 239-4, Moffett Field, CA 94035, United States
AU: Kubo, M D
EM: mkubo@arc.nasa.gov
AF: SETI Institute, NASA Ames Research Center Mail Stop 239-4, Moffett Field, CA 94035, United States
AU: Vogel, M B
EM: mvogel@arc.nasa.gov
AF: Oak Ridge Associated Universities, NASA Ames Research Center Mail Stop 239-4, Moffett Field, CA 94035, United States
AU: Des Marais, D J
EM: David.J.DesMarais@nasa.gov
AF: Exobiology Branch, NASA Ames Research Center Mail Stop 239-4, Moffett Field, CA 94035, United States
AB: Gypsum evaporites host diverse, productive and volumetrically significant microbial communities and are relevant modern-day analogs to both Precambrian sabkha deposits and, potentially, Martian evaporites. Extensive evaporites form in subaqueous environments of high salinity ponds (>150 permil) maintained by the Exportadora de Sal, S. A. (ESSA) in Guerrero Negro, B.C.S., Mexico. A gypsarenite (reworked clastic gypsum) crust found along the southeast margin of ESSA's Pond 9 was collected in February 2004 and each vibrantly colored layer in the top centimeter was sampled. Extant microbial communities from each layer were characterized using complementary culture-independent molecular techniques, lipid biomarker analysis, and compound specific isotopic analysis. Coupling molecular analysis with lipid biomarker analysis revealed that oxygenic photosynthetic organisms dominate the surface layers (top 3 mm). Polar lipids from the surface layers consisted predominantly of glycolipids, which are characteristic of algae, cyanobacteria and green anoxygenic photosynthetic bacteria. Consistent with prior analyses of gypsum evaporites, 16S rRNA gene clone libraries indicate that cyanobacterial populations belong primarily to the genus Cyanothece. The bacterial community below the surface layers is more diverse and dominated by anaerobic organisms. Phototrophic purple sulfur bacteria, sulfate-reducing bacteria (SRB), and Bacteroidetes were particularly abundant. The relative abundances of SRB increased with depth; Desulfobacteraceae clones were distributed throughout the crust, but not at the surface, while Desulfovibrionaceae clones were found predominantly in the deepest layers. These molecular results are consistent with fatty acid biomarker analysis. δ¹³C values of major lipid classes in the crust and sediment range from 14 to 36‰, which is considerably lower than corresponding values for benthic Microcoleus-dominated cyanobacterial mats found at lower salinities at ESSA (65-100‰). A mass balance calculation yields δ¹³C values of approximately 20‰ for the fatty acid fraction in surface layers, only slightly depleted relative to the surface 2 mm of the Microcoleus mat (δ¹³C ~ -17 ‰). The fatty acid fractions in lower anoxic layers are significantly depleted relative to surface crust, with δ¹³C values approaching -26 permil. In contrast, the Microcoleus mats do not exhibit a substantial trend with depth. The isotopic trend with depth in the crusts may reflect isotopic discrimination associated with carbon fixation by non-oxygenic phototrophs and/or chemautotrophs, or changes in the network of carbon flows within the ecosystem.
DE: 0406 Astrobiology and extraterrestrial materials
DE: 0448 Geomicrobiology
DE: 0456 Life in extreme environments
DE: 0465 Microbiology: ecology, physiology and genomics (4840)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting