HR: 1340h
AN: B13A-1039    [Abstracts]
TI: The Experimental Degradation of Microorganisms Exposed to Mn(II) and SiO₂ Over Time
AU: * Schelble, R T
EM: rachels@usc.edu
AF: Department of Earth Science, University of Southern California, 3651 Trousdale Parkway, Los Angeles, CA 90089 United States
AU: * Schelble, R T
EM: rachels@usc.edu
AF: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road NW, Washington, DC 20015 United States
AU: Hall, J A
EM: j.hall@gl.ciw.edu
AF: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road NW, Washington, DC 20015 United States
AU: Fogel, M L
EM: m.fogel@gl.ciw.edu
AF: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road NW, Washington, DC 20015 United States
AU: Jahnke, L L
EM: linda.l.jahnke@nasa.gov
AF: NASA Ames Research Center, Exobiology Branch, Mail Stop 239-4, Moffett Field, CA 94035 United States
AU: Nealson, K H
EM: knealson@usc.edu
AF: Department of Earth Science, University of Southern California, 3651 Trousdale Parkway, Los Angeles, CA 90089 United States
AU: Steele, A
EM: a.steele@gl.ciw.edu
AF: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road NW, Washington, DC 20015 United States
AB: The sedimentary origin of early Proterozoic massive manganese deposits in the geological record is often attributed in part to the impact of biological processes. Although it seems possible that widespread algal blooms in near-shore oceanic environments caused the oxidation of reduced manganese from ocean waters, direct evidence of microorganisms (i.e. microfossils or chemical biosignatures) have not been identified in early Proterozoic manganiferous deposits. The purpose of this study was to identify the potential for biosignature preservation in remnant ancient manganese deposits by monitoring the degradation of modern microorganisms exposed to varying concentrations of Mn(II). Given that most early Proterozoic microfossils have been found in siliceous rocks, similar experiments were carried out using silica-rich solutions for comparison. Bacillus subtilis (gram-positive) and Escherichia coli (gram-negative) were exposed to various Mn(II)- and silica-rich solutions over a period of 180 days. The degradation of a short-duration biomarker (DNA), and longer-duration biomarkers (phospholipid fatty acids and their derivative n-alkanes) were investigated. The degradation of DNA was quantified using real time PCR (RT-PCR) and microorganism specific and general bacteria primers. DNA longevity decreased with higher concentrations of manganese (up to 1000 ppm Mn(II)) when compared with control microorganisms suspended in solutions without manganese. This effect was more dramatic in the E. coli incubations. Relatively steady decreases in the longevity of B. subtilis DNA were observed when cells were exposed to Mn(II). This may be due to the ability of the organism to sporulate, which may protect the DNA from rapid degradation. B. subtilis DNA persisted longer when cells were exposed to undersaturated SiO₂ solution (100 ppm SiO₂), than those exposed to supersaturated SiO₂ solutions (1000 ppm and 3000 ppm). The preservation potential of E. coli DNA showed no differences between undersaturated SiO₂, supersaturated SiO₂, and controls without silica. Lipid degradation experiments are currently in progress. With an understanding of the longevity of biomarkers in Mn(II)- and SiO₂-rich environments we can gain insight into the possibility of discovering the presence and distribution of life during deposition of the sedimentary rock record.
DE: 0419 Biomineralization
DE: 0424 Biosignatures and proxies
DE: 0448 Geomicrobiology
DE: 0461 Metals
DE: 0463 Microbe/mineral interactions
SC: Biogeosciences [B]
MN: Fall Meeting 2005