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Applied and Environmental Microbiology, September 2009, p. 5586-5591, Vol. 75, No. 17
0099-2240/09/$08.00+0     doi:10.1128/AEM.00490-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Extracellular Iron Biomineralization by Photoautotrophic Iron-Oxidizing Bacteria ^,

Jennyfer Miot,^1* Karim Benzerara,¹ Martin Obst,^2,3 Andreas Kappler,³ Florian Hegler,³ Sebastian Schädler,³ Camille Bouchez,¹ François Guyot,¹ and Guillaume Morin¹

Institut de Minéralogie et de Physique des Milieux Condensés, UMR 7590, CNRS, Universités Paris 6 et Paris 7, Paris, and IMPMC, 140 Rue de Lourmel, Paris, France,¹ BIMR, McMaster University, Hamilton, and Canadian Light Source, 101 Perimeter Road, Saskatoon, Saskatchewan, Canada,² Geomicrobiology, Center for Applied Geoscience, University of Tuebingen, Sigwartstrasse 10, 72076 Tuebingen, Germany³

Received 27 February 2009/ Accepted 6 July 2009

Iron oxidation at neutral pH by the phototrophic anaerobic iron-oxidizing bacterium Rhodobacter sp. strain SW2 leads to the formation of iron-rich minerals. These minerals consist mainly of nano-goethite (-FeOOH), which precipitates exclusively outside cells, mostly on polymer fibers emerging from the cells. Scanning transmission X-ray microscopy analyses performed at the C K-edge suggest that these fibers are composed of a mixture of lipids and polysaccharides or of lipopolysaccharides. The iron and the organic carbon contents of these fibers are linearly correlated at the 25-nm scale, which in addition to their texture suggests that these fibers act as a template for mineral precipitation, followed by limited crystal growth. Moreover, we evidence a gradient of the iron oxidation state along the mineralized fibers at the submicrometer scale. Fe minerals on these fibers contain a higher proportion of Fe(III) at cell contact, and the proportion of Fe(II) increases at a distance from the cells. All together, these results demonstrate the primordial role of organic polymers in iron biomineralization and provide first evidence for the existence of a redox gradient around these nonencrusting, Fe-oxidizing bacteria.

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* Corresponding author. Mailing address: IPGP, 140 rue de Lourmel, 75015 Paris, France. Phone: 0033144279832. Fax: 0033144273785. E-mail: miot{at}impmc.jussieu.fr

Published ahead of print on 10 July 2009.

Supplemental material for this article may be found at http://aem.asm.org/.

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Applied and Environmental Microbiology, September 2009, p. 5586-5591, Vol. 75, No. 17
0099-2240/09/$08.00+0     doi:10.1128/AEM.00490-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

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