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Applied and Environmental Microbiology, December 2001, p. 5544-5550, Vol. 67, No. 12
Department of Microbiology, College of
Biological Sciences, University of Guelph, Guelph, Ontario, Canada N1G
2W1
Received 2 April 2001/Accepted 27 August 2001
Shewanella putrefaciens, a gram-negative, facultative
anaerobe, is active in the cycling of iron through its interaction with Fe (hydr)oxides in natural environments. Fine-grained Fe precipitates that are attached to the outer membranes of many gram-negative bacteria
have most often been attributed to precipitation and growth of the
mineral at the cell surface. Our study of the sorption of nonbiogenic
Fe (hydr)oxides revealed, however, that large quantities of
nanometer-scale ferrihydrite (hydrous ferric oxide), goethite (
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.12.5544-5550.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Sorption of Fe (Hydr)Oxides to the Surface of Shewanella
putrefaciens: Cell-Bound Fine-Grained Minerals Are Not Always
Formed De Novo
-FeOOH), and hematite (
-Fe2O3) adhered
to the cell surface. Attempts to separate suspensions of cells and
minerals with an 80% glycerin cushion proved that the sorbed minerals
were tightly attached to the bacteria. The interaction between minerals
and cells resulted in the formation of mineral-cell aggregates, which increased biomass density and provided better sedimentation of mineral
Fe compared to suspensions of minerals alone. Transmission electron
microscopy observations of cells prepared by whole-mount, conventional
embedding, and freeze-substitution methods confirmed the close
association between cells and minerals and suggested that in some
instances, the mineral crystals had even penetrated the outer membrane
and peptidoglycan layers. Given the abundance of these mineral types in
natural environments, the data suggest that not all naturally occurring
cell surface-associated minerals are necessarily formed de novo on the
cell wall.
*
Corresponding author. Mailing address: Department of
Microbiology, College of Biological Sciences, University of Guelph,
Guelph, Ontario, Canada N1G 2W1. Phone: (519) 824-4120, ext. 8904. Fax: (519) 837-1802. E-mail: glasauer{at}micro.uoguelph.ca.
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