HR: 0800h
AN: B21B-0866    [Abstracts]
TI: AFM-Study on Calcite Nucleation by Cyanobacteria
AU: * Obst, M
EM: martin.obst@eawag.ch
AF: Swiss Federal Institute for Environmental Science and Technology, Limnological Research Center, Seestr. 79, Kastanienbaum, 6047 Switzerland
AU: Kuehn, H
EM: info@nanocraft.de
AF: NanoCraft, Innovation Center, Turmstr. 4, Engen, 78234 Germany
AU: Dittrich, M
EM: maria.dittrich@eawag.ch
AF: Swiss Federal Institute for Environmental Science and Technology, Limnological Research Center, Seestr. 79, Kastanienbaum, 6047 Switzerland
AB: Prokaryotic picoplankton plays an important role in lacustrine calcite precipitation, especially in oligotrophic lakes. The mechanisms of cyanobacteria-surface mediated precipitation reactions, however, remain poorly understood. For interpreting geochemical and isotopic information stored in sediments, it is essential to know the carbonate precipitation mechanisms and microscopical details of nucleation on the cell surface. A microscopy study was designed, based on previous results of cyanobacterial calcite precipitation. In order to investigate the nucleation of calcite on the cell surface under controlled conditions, experiments with Synechococcus (PCC 7942) were performed in a flow-through design of an atomic force microscope (AFM). The AFM was operated in `Tapping Mode' providing information on the topography and additionally on physicochemical properties by mapping the phase shift of the oscillating cantilever. For these experiments cells were immobilized on glass slides. As the basic requirement, growth experiments were performed in order to ensure that the fixed cells were alive. To our knowledge one of the first times the successive steps of a cyanobacterial cell division were observed by AFM. The growth of cell agglomerates was monitored over a period of 6 days. AFM images finally reveal the formation of a cyanobacterial biofilm on the glass surface. These observations were supported by the results obtained by epifluorescence microscopy. In a second step, calcite nucleation experiments were performed. Under carefully controlled physical and chemical conditions, nucleation of calcite was enhanced by flushing the fluid cell of the AFM with supersaturated solutions of CaCO$_{3}$ (CaCl$_{2}$ and NaHCO$_{3}$). These solutions were 7 and 10 times supersaturated. As the result of the addition of the CaCO$_3$-solution, changes of the microtopography and physicochemical properties of the cell surface were observed. In our study in-situ-AFM was shown to be powerful tool investigating mechanisms of biomineralization and nucleation under controlled natural conditions.
DE: 4840 Microbiology
DE: 4803 Bacteria
DE: 1845 Limnology
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting