Schematic Illustration.

<p>Representation of passive uptake of Cr-AuNPs by <i>S. oneidensis</i> MR-1 and subsequent Raman Chemical imaging of cells to reveal the intracellular localization of reduced Cr(III) and unreacted Cr(VI).</p

Confocal Raman Mapping.

<p>Raman Intensity Maps averaged over a wide wavenumber region (162–1953 cm⁻¹) covering most of bio-molecular components in cells to obtain a Raman chemical image of the cell (A), Phonon Plasmon peak (207–297 cm⁻¹) originating from gold depicting the presence of Cr-AuNps (B), Cr(VI) - hexavalent chromium (C, 837–873 cm⁻¹), reduced non-toxic trivalent Cr(III) (D, 531–567 cm⁻¹). Raman images in grid format, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0016634#pone-0016634-g006" target="_blank">Fig. 6E and 6F</a> are representations of 6B and 6C respectively. 6-E* and F* represent magnified pixel plots to demonstrate the overlap in signal of Au and Cr(VI) peaks within cells.</p

Confocal Fluorescence Lifetime Imaging.

<p><i>S. oneidensis</i> MR-1 incubated with 3.5 nm (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0016634#pone-0016634-g007" target="_blank">Fig. 7A & 7C</a>) and 13 nm (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0016634#pone-0016634-g007" target="_blank">Fig. 7B & 7D</a>) Cr-AuNp probes show scattered low-lifetime (blue) distribution indicating the presence of gold nanoparticles (both internalized and externally bound) compared to the control incubated with plain gold nanoparticles (inset - 7A).</p

Thin-section TEM Images of <i>S. oneidensis</i> MR-1.

<p>A. without particles, B. plain 13 nm gold Nanoparticles, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0016634#pone-0016634-g004" target="_blank">Fig. 4C–4D</a>. Chromate coated gold nanoparticles, Cr-AuNp:13 nm, (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0016634#pone-0016634-g004" target="_blank">Fig. 4E–4F</a>) 3.5 nm Cr-AuNp. Red arrows indicate extracellularly bound Cr-AuNp and green arrows/circle indicate internalized particles. (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0016634#pone-0016634-g004" target="_blank">Fig. 4G–4H</a>) show 3.5 nm and 13 nm probes used in Cr-AuNp preparation.</p

Inductively Coupled Mass-Spectrometry.

<p>A. ICP-MS Calibration curve for Cr quantification. B. Intracellularly trapped Cr(VI) and Cr(III) at time t = 0 and t = 12 h after Cr-AuNp treatment.</p

Effect of Cr-AuNPs on the growth of <i>Shewanella oneidensis</i> MR-1.

<p>Either 3.5 nm (closed symbols) or 13 nm (open symbols) Cr-AuNPs were added to wells at volumes of 0, 5, 10, and 50 µl. Error bars represent the standard error from three independent cultures.</p

Effect of Cr-AuNPs on chromate reduction by <i>S. oneidensis</i> MR-1.

<p>Abiotic controls were included to rule out the reduction of chromate by media components and the Cr-AuNPs (open symbols). There was no adverse effect on chromate reduction ability induced by the nanoparticles (closed symbols). In addition, the nanoparticles did not directly reduce the chromate in the medium in the absence of cells (open symbols). Error bars represent the standard error from three independent cultures.</p