Microbial Reduction of Lepidocrocite γ-FeOOH by Shewanella putrefaciens; The Formation of Green Rust

Abstract

Dissimilatory iron-reducing bacteria (DIRB) couple the oxidation of organic matter or H₂ to the reduction of iron oxides. The bacterial reduction of a most common well-crystallised ferric oxyhydroxide, γ-FeOOH was investigated using DIRB Shewanella putrefaciens, strain CIP 8040. Experiments were conducted in the presence of neither organic buffer nor phosphate, with formate as electron donor, bicarbonate, and anthraquinone-2,6-disulfonate (AQDS, a humic acid analogue) that influenced the extent of ferric oxide bioreduction. The production of Fe²⁺ was followed with time. The solid phases obtained after bacterial iron reduction were analysed by transmission Mössbauer spectroscopy (TMS) and X-ray diffraction (XRD). Biogenic formation of green rust 1 compound, which contains carbonate anions, [Fe^II ₂Fe^III ₂(OH)₈]²⁺⋅[CO₃ ²⁻]²⁻ was observed. TMS was used to follow the evolution of the green rust abundance during the bacterial culture.