Bioreduction of Pt(IV) from aqueous solution using sulphate-reducing bacteria

The aims of this study were to investigate the role of sulphate-reducing bacteria in facilitating Pt removal from aqueous solutions and to investigate the role of a hydrogenase enzyme in Pt reduction in vitro. To avoid precipitation of Pt as Pt sulphide, a resting (non-growing) mixed culture was used. A pH-dependent rate of Pt removal from aqueous solution was observed, indicating that metal speciation was the main factor for its removal from solution. The maximum initial concentration of Pt(IV) that the cells can effectively remove from solution was 50 mg/l, while the maximum capacity was only 4 mg of Pt per gram of resting biomass. Transmission electron microscopy and energy dispersive X-ray analyses indicated that Pt was being precipitated in the periplasm, a major area of hydrogenase activity in the cells. In vitro investigation of Pt reduction with hydrogen as the electron donor showed that 49% was removed within 1 h when a relatively pure hydrogenase extract was used, 31% was removed with a cell-free soluble extract and 70% removed by live cells.