Breathing metals as a way of life: geobiology in action.

Many microbes have the ability to reduce transition metals, coupling this reduction to the oxidation of energy sources in a dissimilatory fashion. Because of their abundance, iron and manganese have been extensively studied, and it is well established that reduction of Mn and Fe account for significant turnover of organic carbon in many environments. In addition, many of the dissimilatory metal reducing bacteria (DMRB) also reduce other metals, including toxic metals like Cr(VI), and radioactive contaminants like U(VI), raising the expectations that these processes can be used for bioremediation. The processes involved in metal reduction remain mysterious, and often progress is slow, as nearly all iron and manganese oxides are solids, which offer particular challenges with regard to imaging and chemical measurements. In particular, the interactions that occur at the bacteria-mineral interfaces are not yet clearly elucidated. One DMRB, Shewanella oneidensis MR-I offers the advantage that its genome has recently been sequenced, and with the availability of its genomic sequence, several aspects of its metal reducing abilities are now beginning to be seen. As these studies progress, it should be possible to separate several processes involved with metal reduction, including surface recognition, attachment, metal destabilization and reduction, and secondary mineral formation.