Reduction of ferric green rust by Shewanella putrefaciens

F Jorand,A Zegeye,C Ruby,F Landry

doi:10.1111/j.1472-765x.2007.02225.x

Abstract

To reduce carbonated ferric green rust (GR*) using an iron respiring bacterium and obtain its reduced homologue, the mixed Fe(II)-Fe(III) carbonated green rust (GR). The GR* was chemically synthesized by oxidation of the GR and was incubated with Shewanella putrefaciens cells at a defined [Fe(III)]/[cell] ratio. Sodium methanoate served as the sole electron donor. The GR* was quickly transformed in GR (iron reducing rate = 8.7 mmol l(-1) h(-1)). Ferric green rust is available for S. putrefaciens respiration as an electron acceptor. The reversibility of the GR redox state can be driven by bacterial activity. This work suggests that GRs would act as an electronic balance in presence of bacteria. It provides also new perspectives for using iron reducing bacterial activity to regenerate the reactive form of GR during soil or water decontamination processes.

Highlights

The mixed valence compound fougerite (IMA 2003-057), a layered FeII–FeIII hydroxysalt called green rust, is found in transitionally oxic and anoxic environments like hydromorphic soils (Trolard et al 1996; Genin et al 1998)
The initial rate of reduction was 8Æ7 mmol l)1 h)1 (SD = 5%). This is the fastest reduction rate for iron bioreducing systems leading to FeII–FeIII green rust (GR) formation
We demonstrate in the present study that the ferric oxyhydroxide GR* can serve as an electron acceptor for Shewanella cells

Summary

Introduction

The mixed valence compound fougerite (IMA 2003-057), a layered FeII–FeIII hydroxysalt called green rust, is found in transitionally oxic and anoxic environments like hydromorphic soils (Trolard et al 1996; Genin et al 1998). Green rusts are constituted of FeII–FeIII hydroxide sheets separated by interlayers of anions and water molecules balancing the cation layer charge. The formula FeII4 FeIII2(OH)12CO33H2O has been proposed for the stoichiometric mixed FeII–FeIII carbonated green rust (GR) (Hansen 2001). The variation of the [FeIII] ⁄ [Fetotal] ratio of the fougerite would correspond to different oxidation states of the green rust compounds (Genin et al 2005; Ruby et al 2006) where the fully oxidized state corresponds to the GR*. GR can be the by-products of iron respiring bacteria when two-line ferrihydrite or lepidocrocite (c-FeOOH) are the starting FeIII substrate (Parmar et al 2001; Glasauer et al 2002; Ona-Nguema et al 2002; Zachara et al 2002; Zegeye et al 2005)

Methods

Results

Conclusion