Magnetotactic bacteria as an effective sorbent for uranium in contaminated water.

There are many ideas for using radionuclide- and heavy metal-binding microorganisms to remediate contaminated waters after e.g. uranium mining and processing. In particular, magnetotactic bacteria are moving into the focus of interest since they are able to survive in environments with very limited oxygen. Due to their organelles containing magnetic crystals, they can align themselves along the Earth's magnetic field for reaching regions of optimal oxygen concentrations. In laboratory studies we used the α-proteobacterium Magnetospirillum magneticum AMB-1, which is a motile, magnetotactic, gram-negative bacterium. It is facultative anaerobe and usually found in oxic-anoxic transition zones. In kinetic batch sorption experiments, cells of Magnetospirillum magneticum AMB-1 were contacted with different uranium concentrations and different pH. Independent of the initial U concentration, the cells were able to remove most of the uranium from the solution during the first hours of incubation. Microscopic studies, such as Transmission Electron Microscopy (TEM) in combination with Energy-Dispersive X-ray Spectroscopy (EDXS), clearly indicated that uranium is entirely accumulated in the cell membrane. Using spectroscopic methods like Time-Resolved Laser-Induced Fluorescence Spectroscopy at low temperature (cryo-TRLFS at 153 K), it was shown that uranium is mainly bound to the carboxylic functionality groups of peptidoglycan at the outer membrane of Magnetospirillum magneticum AMB-1 cells. With the obtained results we demonstrate that magnetotactic bacteria may play an important role in the bioremediation of contaminated sites, and probably not only for uranium, but also for other heavy metals.