Synchrotron XRF Microscopy of the Elemental Concentration Gradients in Association with S. oneidensis MR-1 Cells

<p>False-color micro-XRF maps of qualitative spatial distributions and concentration gradients of P, U, and Fe in and around MR-1 cells. Cells are shown after incubation with 250 μM U(VI) for 24 h in standard assay conditions (A). The extracellular UO₂ precipitates associated with EPS (B) and diffuse extracellular UO₂ nanoparticles (C) observed in MR-1 samples were also evaluated for elemental composition. The scanned regions are represented with each corresponding thin-section TEM image. (D) The UO₂-EPS features seen in (B) were scanned vertically six times longer per point, and the pixel intensity (identified between the dashed lines) was plotted for each element. Although this image is of a smaller area and has a smaller number of features in its field of view, the increased measurement time provides more robust statistics and further supports co-localization of the elements.