Bioreduction of biotite and chlorite by a Shewanella species

The interactions between the Fe(III)-reducing bacterium Shewanella oneidensis MR-1 and the phyllosilicate minerals biotite and chlorite have been studied. In washed, non-growing cell suspensions, S. oneidensis MR-1 was able to mediate the reduction of Fe(III) in biotite and chlorite in the presence and absence of an artificial electron shuttle, and to reduce as much as 36% of the starting Fe(III) in biotite, and 21% in chlorite. This is predominantly a solid-state reaction, as no significant dissolution or change in morphology was observed after microbial reduction. In growing-cell experiments, with Fe(III) as the only electron acceptor, bacterial biomass increased over eight weeks of incubation. Combining the results of (weak acid-extractable) iron characterization by ferrozine assay and bulk solid iron mineral characterization using Mossbauer spectroscopy, has led to the development of a possible mechanism of reduction of Fe(III) in the bulk of the mineral. Long-distance electron transfer between M2 sites along octahedral layers may facilitate the reduction of the bulk mineral. To our knowledge, this is the first study to demonstrate microbially mediated reduction of Fe(III) within biotite, and show the ability of S. oneidensis MR-1 to conserve energy for growth from this reduction.