Formation of Hydroxysulphate Green Rust 2 as a Single Iron(II-III) Mineral in Microbial Culture

Although GR2(SO₄ ^2-) can be easily formed by abiotic synthesis, the biotic formation of hydroxysulphate as a single iron(II-III) mineral in microbial culture and its characterization was not achieved. This study was carried out to investigate the sole formation of GR2(SO₄ ^2-) during the reduction of γ-FeOOH by a dissimilatory iron-respiring bacterium, Shewanella putrefaciens CIP 8040^T. Reduction experiments were performed in a non-buffered medium devoid of organic compounds, with 25 mM of sulphate and with a range of lepidocrocite concentrations with H₂ as the electron donor under nongrowth conditions. The resulting biogenic solids, after iron-respiring activity, were characterized by X-ray diffraction (XRD), transmission Mössbauer spectroscopy (TMS) and electron microscopy (SEM and TEM). The sulphate has been identified as the intercalated anion by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). In addition, the structure of this sulphate anion was discussed. Our experimental study demonstrated that, under H₂ atmosphere, the biogenic solid was a GR2(SO₄ ^2-), as the sole iron(II-III) bearing mineral, whatever the initial lepidocrocite concentration. The crystals of the biotically formed GR2(SO₄ ^2-) are significantly larger than those observed for GR2(SO₄ ^2-) obtained through abiotic preparation, < 15 μ m diameter as against 0.5–4 μm, respectively.

Keywords:

• hydroxysulphate GR2
• Shewanella putrefaciens
• biomineralization
• bacterial iron reduction
• diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS)
• Mössbauer spectroscopy
• XRD
• MET
• lepidocrocite

The authors acknowledge S. Borensztajn of the Laboratoire de Physique des Liquides et Electrochimie (Paris 6 University) for the SEM-EDS analyses. We thank R. Aissa of the Laboratoire de Chimie Physique et Microbiologie pour l'Environnement for providing us with abiotic GR. We also thank I. Bihannic from the Laboratoire Environnement et Minéralurgie for the XRD analyses and J. Ghanbaja (Nancy I University) for the TEM analyses.

Notes

*This work: characterisation after

^a 14 days and

^b 90 days of incubation

^c (Simon et al. 1997)

^d (Hansen et al. 1994)

^e (Ona-Nguema et al. 2004).