HR: 1340h
AN: B13A-1045    [Abstracts]
TI: Microbial Mediation of Dolomite Precipitation in Natural Environments, Culture Experiments and Molecular Studies
AU: * Meister, P
EM: pmeister@usc.edu
AF: Earth Sciences, USC, 3651 Trousdale Parkway, Los Angeles, CA 90089-0740 United States
AU: Nealson, K
EM: knealson@usc.edu
AF: Earth Sciences, USC, 3651 Trousdale Parkway, Los Angeles, CA 90089-0740 United States
AU: McKenzie, J A
EM: sediment@erdw.ethz.ch
AF: Geological Institute, ETH Zentrum , Zuerich, ZH 8092 Switzerland
AU: Warthmann, R
EM: warthmann@erdw.ethz.ch
AF: Geological Institute, ETH Zentrum , Zuerich, ZH 8092 Switzerland
AU: Vasconcelos, C
EM: cris.vasconcelos@erdw.ethz.ch
AF: Geological Institute, ETH Zentrum , Zuerich, ZH 8092 Switzerland
AB: Although dolomite [CaMg(CO3)2] is a common carbonate mineral in sedimentary rocks, it is rarely observed forming in modern environments, and, until recently, experimental precipitation under Earth surface conditions proved impossible. With the discovery of microbial mediated dolomite formation in culture experiments with sulfate-reducing bacteria, it has become apparent that microbes play an important role in overcoming the kinetic barrier of mineral precipitation and, thus, may represent a key factor controlling early diagenetic processes throughout Earth history. The detailed mechanisms of these processes, however, remain poorly understood. Recent studies of dolomite layers in organic carbon-rich hemipelagic sediments recovered on the Peru margin during Ocean Drilling Program Leg 201 (Meister et al., in prep.) indicate precipitation at the interface between the sulphate reduction and methanogenic zones. At this chemical front, alkalinity is strongly increased, sulphate ions, a possible inhibitor of dolomite precipitation, are efficiently removed, and highest total cell densities were counted (up to 10 to the 9 cells / cm3; Shipboard Scientific Party, 2003). These results strengthen the model that microbes are involved in dolomite formation, providing the appropriate chemical conditions, whereas the high cell density may kinetically control the strictly focused precipitation process. We are currently conducting a systematic study of the precipitation of dolomite and other carbonate minerals in the Ca-Mg-bicarbonate-system. In preliminary experiments under aerobic conditions we used agar plates with a marine medium to grow a bacterium isolated from sediments of the San Pedro basin (California), an upwelling area similar to the Peru margin. We observed that the crystals formed only inside of the colonies and showed a dumbbell-shaped morphology similar to dolomite produced in anaerobic experiments. X-ray diffraction patterns revealed, however, that the product was exclusively aragonite instead of dolomite. Our results confirm previous studies indicating that bacterial activity can significantly influence rate, mineralogy, shape, stoichiometry and, perhaps, even isotopic fractionation during mineral formation. The mechanism(s) may be related either to the structure of the cell surface, per se, or to extracellular polymeric substances and their functional groups. Additionally, a direct control through specific enzymes cannot be excluded. We are currently using a genetic screen to elucidate possible mechanisms. The discovery of knockout mutants unable to mediate dolomite formation will provide a better understanding of the mechanisms used by microorganisms to mediate mineral formation. Such studies will yield information to better interpret diagenetic phenomena, in general, as well as dolomite formation associated with the modern subseafloor biosphere and in the geologic record, e.g., the Miocene Monterey Formation (CA).
UR: http://www.usc.edu/dept/earth/research/geobiology.html
DE: 0419 Biomineralization
DE: 0420 Biomolecular and chemical tracers
DE: 0448 Geomicrobiology
DE: 0456 Life in extreme environments
DE: 0463 Microbe/mineral interactions
SC: Biogeosciences [B]
MN: Fall Meeting 2005