The effect of Fe on Si adsorption by Bacillus subtilis cell walls: insights into non-metabolic bacterial precipitation of silicate minerals |
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| Institution: | 1. Forschungszentrum Jülich GmbH, Garching, Germany;2. Forschungszentrum Jülich GmbH, Jülich, Germany;1. Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA;2. Department of Geological Sciences, University of Missouri, Columbia, MO 65211, USA;3. Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, ON L5L 1C6, Canada;4. AECOM, Germantown, MD 20876, USA;5. Department of Geological Sciences, Stanford University, Stanford, CA 94305, USA;6. Geophysical Laboratory, Carnegie Institution for Science, Washington, DC 20015, USA;7. Department of Geosciences, Virginia Tech, Blacksburg, VA 24061, USA;8. School of Biological, Earth, and Environmental Sciences, University College Cork, Cork, T23 TK30, Ireland;9. Department of Geological Sciences, SUNY Geneseo, Geneseo, NY 14454, USA;10. Department of Geosciences, University of Montana, Missoula, MT 59812, USA |
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| Abstract: | Si adsorption onto Bacillus subtilis and Fe and Al oxide coated cells of B. subtilis was measured both as a function of pH and of bacterial concentration in suspension in order to gain insight into the mechanism of association between silica and silicate precipitates and bacterial cell walls. All experiments were conducted in undersaturated solutions with respect to silicate mineral phases in order to isolate the important adsorption reactions from precipitation kinetics effects of bacterial surfaces. The experimental results indicate that there is little association between aqueous Si and the bacterial surface, even under low pH conditions where most of the organic acid functional groups that are present on the bacterial surface are fully protonated and neutrally charged. Conversely, Fe and Al oxide coated bacteria, and Fe oxide precipitates only, all bind significant concentrations of aqueous Si over a wide range of pH conditions. Our results are consistent with those of Konhauser et al. Geology 21 (1993) 1103; Environ. Microbiol. 60 (1994) 49] and Konhauser and Urrutia Chem. Geol. 161 (1999) 399] in that they suggest that the association between silicate minerals and bacterial surfaces is not caused by direct Si–bacteria interactions. Rather, the association is most likely caused by the adsorption of Si onto Fe and Al oxides which are electrostatically bound to the bacterial surface. Therefore, the role of bacteria in silica and silicate mineralization is to concentrate Fe and Al through adsorption and/or precipitation reactions. Bacteria serve as bases, or perhaps templates, for Fe and Al oxide precipitation, and it is these oxide mineral surfaces (and perhaps other metal oxide surfaces as well) that are reactive with aqueous Si, forming surface complexes that are the precursors to the formation of silica and silicate minerals. |
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