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Miot, Jennyfer ; Benzerara, Karim ; Obst, Martin ; Kappler, Andreas ; Hegler, Florian ; Schädler, Sebastian ; Bouchez, Camille ; Guyot, François ; Morin, Guillaume:
Extracellular Iron Biomineralization by Photoautotrophic Iron-Oxidizing Bacteria.
In: Applied and Environmental Microbiology.
Bd. 75
(2009)
Heft 17
.
- S. 5586-5591.
ISSN 1098-5336
DOI: https://doi.org/10.1128/AEM.00490-09
Abstract
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 (α-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.