Dependence of Secondary Mineral Formation on Fe(II) Production from Ferrihydrite Reduction by Shewanella oneidensis MR-1

Although dissimilatory iron reduction and secondary mineral formation by Shewanella oneidensis MR-1 have been widely recognized, questions remain about the effects of biogenic Fe(II) on the rate and extent of secondary mineral formation and the importance of biogenic Fe(II)-induced crystallization processes. In this study, we investigated the effects of different mutants of MR-1 on the bioreduction and mineralization of ferrihydrite. The results indicate that while the reduction rates of ferrihydrite by ΔmtrD, ΔmtrF, and ΔomcA are similar to that of the wild type (WT), the capacity to reduce ferrihydrite decreased dramatically in the mutants ΔcymA and ΔmtrA. The order for Fe(III) reduction by MR-1 WT and mutants was ranked as follows: WT ≈ ΔmtrD ≈ ΔmtrF > ΔomcA > ΔmtrC > ΔcymA > ΔmtrA. Secondary minerals of ferrihydrite were characterized using X-ray diffraction, Fourier transform infrared spectra, and scanning electron microscopy. The results show that goethite and hematite were the main secondary minera...