Extracellular Iron Biomineralization by Photoautotrophic Iron-Oxidizing Bacteria

Jennyfer Miot (1) , Karim Benzerara (1) , Martin Obst (2, 3) , Andreas Kappler (2) , Florian Hegler (2) , Sebastian Schädler (2) , Camille Bouchez (1) , François Guyot (1) , Guillaume Morin (1)

1 IMPMC - Institut de minéralogie, de physique des matériaux et de cosmochimie
2 ZAG - Center for Applied Geoscience [Tübingen]
3 BIMR - Brockhouse Institute for Materials Research

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.

Domains: Bacteriology; Earth Sciences

Jennyfer Miot, Karim Benzerara, Martin Obst, Andreas Kappler, Florian Hegler, et al.. Extracellular Iron Biomineralization by Photoautotrophic Iron-Oxidizing Bacteria. Applied and Environmental Microbiology, 2009, 75 (17), pp.5586-5591. ⟨10.1128/AEM.00490-09⟩. ⟨insu-01516127⟩