Panels F, G, and H show images of a control cell, grown in the absence of SeO3 2- , but otherwise treated identically to the cell in panel A (including Cu 2+ exposure). There are no obvious punctate densities in this tomogram. Automatic segmentation does not identify voxels of intensity comparable to those in the experimental cell. An additional control, of cells expressing the Se-reducing GRLMR enzyme and grown in SeO3 2- supplemented media was published previously. In that experiment, SeNPs with diameters ranging between 5 and 60 nm were distributed in cells without any apparent organization. FtsZ localizes ~16 nm from the inner membrane,[cite] which is ~30 nm from the reliably segmented OM. Therefore, CuSeNPs that observed about ~45nm of the outer membrane are plausibly associated with FtsZ protofilaments. Figure , panel I shows a histogram of CuSeNP -membrane distances for the cell in panel A. 94% of cSeNPs ( 98 of 104 total) are within 45 nm of the outer membrane. Of those, 37% are closer than 16 nm to the outer membrane. We attribute particles closer than 16nm to the outer membrane to membrane fixation artefacts. Therefore, the vast majority of observed CuSeNPs lie in plausible FtsZ associated locations.