To stain bacterial and Vero cell nucleic acids, 4′,6-diamidino-2-phenylindole (DAPI) was included during the secondary incubation. Micrograph images were captured using a Nikon DS FI1 camera on a Nikon Eclipse TE 2000-S microscope at × 600 magnification with nis-elements f 3.00 software. All micrograph size and merge functions were performed universally for the associated micrographs

using imagej version 1.42n (Wayne Rasband, NIH). To observe the localization of IcmT, IcmV, and DotH at the ultrastructural level, infected Vero cells as described previously were prepared for IEM. To do this, infected cells were trypsinized, pelleted, and fixed on ice for 1 h in PBS, 4% paraformaldehyde (v/v), and 0.05% glutaraldehyde

(v/v). The Imaging Facility at the Department of Molecular Microbiology Center for Infectious Disease Research, Washington University, St. Louis, NVP-BEZ235 molecular weight MO, performed the subsequent sample processing and IEM analyses following published techniques (Presti et al., 2009). After incubation with primary antibodies against IcmT, IcmV, and DotH, respectively, sections were then washed in blocking buffer and probed with anti-rabbit IgG (H+L) conjugated to 18 nm colloidal gold (Jackson ImmunoResearch Laboratories Inc., West Grove, PA) for 1 h at room temperature. After extensive buffer washing, water rinse, and uranyl acetate and lead citrate staining, samples were viewed using a GPCR & G Protein inhibitor JEOL 1200EX transmission electron microscope (JEOL USA Inc., Peabody, MA). The labeling experiments were conducted in parallel with controls omitting the primary antibody. These controls were consistently almost negative at the concentration of the colloidal gold-conjugated secondary antibodies used in these studies. Coxiella burnetii-infected Vero cells were fixed with 2.5% paraformaldehyde (v/v)/2.5% glutaraldehyde (v/v) for transmission electron microscopic analysis as described previously (Belland et al., 2003).

In an effort to determine the subcellular localization of the C. burnetii T4BSS, IFA analyses using antibodies against IcmT, IcmV, and DotH, respectively, were used. Continuously infected cells were used in this analysis in an effort to observe all possible aspects of the C. burnetii infectious cycle, which includes newly infected cells, cells at midinfection, and cells at or near lysis. IFA microscopy of C. burnetii-infected Vero cells shows bacterial cells with both polar and bipolar localization of the T4BSS proteins as indicated by fluorescence of the protein-specific antibodies (Fig. 1a–d). Polar localization of the C. burnetii T4BSS proteins is readily discernable in the enlarged panels (Fig. 1b–d insets, arrows). In addition, we observe bipolar localization in approximately 60% of the cells that demonstrate polarity (Fig. 1b).