HR: 1330h
AN: B12B-0778    [PDF]
TI: Microbial Biosignatures in High Iron Thermal Springs
AU: * Parenteau, M N
EM: parentea@pdx.edu
AF: Geomicrobiology and Electron Microscopy Laboratory, Department of Geology, Portland State University, 1721 SW Broadway, Portland, OR 97201 United States
AU: Embaye, T
EM: tembaye@mail.arc.nasa.gov
AF: SETI Institute, 2035 Landings Drive, Mountain View, CA 94043 United States
AU: Jahnke, L L
EM: ljahnke@mail.arc.nasa.gov
AF: Exobiology Branch, NASA Ames Research Center, M/S 239-4, Moffett Field, CA 94035 United States
AU: Cady, S L
EM: cadys@pdx.edu
AF: Geomicrobiology and Electron Microscopy Laboratory, Department of Geology, Portland State University, 1721 SW Broadway, Portland, OR 97201 United States
AB: The emerging anoxic source waters at Chocolate Pots hot springs in Yellowstone National Park contain 2.6 to 11.2 mg/L Fe(II) and are 51-$54\deg$C and pH 5.5-6.0. These waters flow down the accumulating iron deposits and over three major phototrophic mat communities: {\it Synechococcus/Chloroflexus} at 51-$54\deg$C, {\it Pseudanabaena} at 51-$54\deg$C, and a narrow {\it Oscillatoria} at 36-$45\deg$C. We are assessing the contribution of the phototrophs to biosignature formation in this high iron system. These biosignatures can be used to assess the biological contribution to ancient iron deposits on Earth (e.g. Precambrian Banded Iron Formations) and, potentially, to those found on Mars. Most studies to date have focused on chemotrophic iron-oxidizing communities; however, recent research has demonstrated that phototrophs have a significant physiological impact on these iron thermal springs (Pierson et al. 1999, Pierson and Parenteau 2000, and Trouwborst et al., 2003). We completed a survey of the microfossils, biominerals, biofabrics, and lipid biomarkers in the phototrophic mats and stromatolitic iron deposits using scanning and transmission electron microscopy (SEM and TEM), energy dispersive spectrometry (EDS), powder X-ray diffraction (XRD), and gas chromatography-mass spectroscopy (GC-MS). The {\it Synechococcus/Chloroflexus} mat was heavily encrusted with iron silicates while the narrow {\it Oscillatoria} mat was encrusted primarily with iron oxides. Encrustation of the cells increased with depth in the mats. Amorphous 2-line ferrihydrite is the primary precipitate in the spring and the only iron oxide mineral associated with the mats. Goethite, hematite, and siderite were detected in dry sediment samples on the face of the main iron deposit. Analysis of polar lipid fatty acid methyl esters (FAME) generated a suite of lipid biomarkers. The {\it Synechococcus/Chloroflexus} mat contained two mono-unsaturated isomers of n-C$_{18:1}$ with smaller amounts of polyunsaturated n-C$_{18:2}$, characteristic of cyanobacteria. The mat also contained abundant n,n-wax esters of C$_{32}$ to C$_{37}$, characteristic of {\it Chloroflexus}. 10-Methyl-C$_{16}$ was also detected, indicative of sulfate reducing bacteria (SRB). The narrow {\it Oscillatoria} mat was dominated by the aforementioned cyanobacterial biomarkers as well as iso-C$_{17:1}$, a biomarker for some groups of SRB. Unusual dimethyl fatty acids were also detected. The goal of this research is to provide an initial dataset that will illustrate the maximum amount of paleobiological and paleoenvironmental information expected to form in these types of iron deposits. Insights from our research may help elucidate the role of phototrophs in the deposition of BIFs on Earth, and may assist in the search for evidence of fossilized microbial life in iron deposits on Mars. Pierson, B.K., M.N. Parenteau, and B.M. Griffin, Phototrophs in high-iron-concentration microbial mats: Ecology of phototrophs in an iron-depositing hot spring, {\it Appl. Environ. Microbiol., 65}, 5474-5483, 1999. Pierson, B.K., and M.N. Parenteau, Phototrophs in high iron microbial mats: Microstructure of mats in iron-depositing hot springs, {\it FEMS Microbiology Ecology 32}, 181-196, 2000. Trouwborst, R., G. Koch, G. Luther, and B.K. Pierson, Photosynthesis and iron in hot spring microbial mats (abstract), NAI General Meeting, {\it Astrobiology 2}(4), 206, 2003.
DE: 3030 Micropaleontology
DE: 4803 Bacteria
DE: 4805 Biogeochemical cycles (1615)
DE: 4832 Hydrothermal systems
DE: 4853 Photosynthesis
SC: Biogeosciences [B]
MN: 2003 Fall Meeting