Intracellular uranium accumulation by Shewanella sp. HN-41 under the thiosulfate-reducing condition

A strain of genus Shewanella, one of representative dissimilatory Fe(III)-reducing bacteria, HN-41 precipitated intraand extracellular needle-like uranium materials in the anaerobic incubation with uranyl acetate (U(VI)O₂ ²⁺) and sodium thiosulfate (S₂O₃ ^2-) as the possible electron acceptors. In the absence of thiosulfate, strain HN-41 generated only fine-grained extracellular U precipitates, presumably mineral uraninite (U(IV)O₂). Electron microscopy showed that the needle-like U precipitates were associated with the inner and outer membranes of strain HN-41 cells incubated anaerobically with thiosulfate. Energy-dispersive X-ray spectroscopy and associated mapping analyses on a single intracellular needle-like particle indicated the compositions of U, P, and S, which lead to inference of the precipitates consisting of uraninite, phosphate, and sulfide. The results indicate that the presence of competing electron acceptors may significantly alter the forms and locations of U biomineralization products.