Extracellular iron biomineralization by photoautotrophic iron-oxidizing bacteria.
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 (alpha-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.
Miot
Jennyfer
J
Institut de Minéralogie et de Physique des Milieux Condensés, UMR 7590, CNRS, Universités Paris 6 et Paris 7, Paris, France. miot@impmc.jussieu.fr
Benzerara
Karim
K
Obst
Martin
M
Kappler
Andreas
A
Hegler
Florian
F
Schädler
Sebastian
S
Bouchez
Camille
C
Guyot
François
F
Morin
Guillaume
G
D001704:Biopolymers / Q000737:chemistry / Q000378:metabolism; D005290:Ferric Compounds / Q000032:analysis; D005296:Ferrous Compounds / Q000032:analysis; D058085:Iron Compounds / Q000737:chemistry / Q000378:metabolism*; D008055:Lipids / Q000032:analysis; D008070:Lipopolysaccharides / Q000032:analysis; D017348:Microscopy, Electron, Scanning Transmission; D008903:Minerals / Q000378:metabolism; D010084:Oxidation-Reduction; D011134:Polysaccharides / Q000032:analysis; D016992:Rhodobacter / Q000378:metabolism*
D001704:Biopolymers; D005290:Ferric Compounds; D005296:Ferrous Compounds; D058085:Iron Compounds; D008055:Lipids; D008070:Lipopolysaccharides; D008903:Minerals; D011134:Polysaccharides