Uranium (VI) reduction by an iron-reducing Desulfitobacterium species as single cells and in artificial multispecies...

Microbial U(VI) reduction plays a major role in new bioremediation strategies for radionuclide-contaminated environments and can potentially affect the safe disposal of high-level radioactive waste in a deep geological repository. Desulfitobacterium sp. G1-2, isolated from a bentonite sample, was used to investigate its potential to reduce U(VI) in different background electrolytes: bicarbonate buffer, where a uranyl(VI)‑carbonate complex predominates, and synthetic Opalinus Clay pore water, where a uranyl(VI)-lactate complex occurs, as confirmed by time-resolved laser-induced fluorescence spectroscopic measurements. While Desulfitobacterium sp. G1-2 rapidly removed almost all U from the supernatants in bicarbonate buffer, only a low amount of U was removed in Opalinus Clay pore water. UV/Vis measurements suggest a speciation-dependent reduction by the microorganism. Scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy revealed the formation of two different U-containing nanoparticles inside the cells. In a subsequent step, artificial multispecies bio-aggregates were formed using derivatized polyelectrolytes with cells of Desulfitobacterium sp. G1-2 and Cobetia marina DSM 50416 to assess their potential for U(VI) reduction under aerobic and anaerobic conditions. These findings provide new perspectives on microbial U(VI) reduction and contribute to the development of a safety concept for high-level radioactive waste repositories, as well as to new bioremediation strategies.