Distinct Magnetic Properties of Magnetite Formed by Dissimilatory Iron Reducers

While dissimilatory iron reducers are known to produce magnetite under laboratory conditions, it is thought that the physical properties of these minerals are a function of the solution chemistry and not of the specific bacteria involved in the reduction of ferric iron. However, a comparison of three strains from the genus Shewanella suggest that there are differences in the physical characteristics of the magnetite produced as a result of dissimilatory iron reduction based on which bacterial strain is used. Strains CN32, MR-4 and W3-18-1 were incubated with lactate as the terminal electron donor and energy source, and hydrous ferric oxide (HFO) as the terminal electron acceptor. The magnetic properties of the biomineral products were examined using susceptibility, hysteresis and cooercivity. Results show that while strains CN32 and MR-4 produce minerals with the magnetic characteristics of superparamagnetic crystals, the magnetite biominerals produced by strain W3-18-1 have much different magnetic properties.