Fig. 1.

The T. pallidum cell envelope. a T. pallidum’s major immunogens are associated with the protoplasmic cylinder, not the outer membrane. Reactivity with human syphilitic serum of proteins extracted with Triton X-114 from whole T. pallidum cells (lane 1), protoplasmic cylinders (lane 2), and solubilized outer membranes (lane 3); reproduced from reference (Radolf et al. 1988). b Freeze-fracture EM reveals scarce intramembranous particles (IMPs) within the T. pallidum OM. Convex and concave leaflets of the OM are indicated. Bar, 0.5 μM. Reproduced from reference (Radolf et al. 1994). c Deep etching reveals that OM intramembranous particles are surface-exposed. Arrowheads indicate the boundaries separating the bacterial surface from the convex fracture face. Particles on the convex fracture face and the treponemal surface are indicated by thin and medium-thickness arrows, respectively. Bar, 0.5 μM. Reproduced from reference (Bourell et al. 1994). d TX-114 phase partitioning reveals that the syphilis spirochete’s major immunogens (based on reactivity with human syphilitic serum) possess hydrophobic character. Lanes: 1. Percoll-purified T. pallidum. 2. TX-114-insoluble material. 3. TX114 detergent-enriched phase proteins. 4. aqueous phase proteins. Reproduced from Reference (Radolf et al. 1988). e Scanning probe microscopy reveals rare particles on the T. pallidum surface; reproduced with permission from reference (Liu et al. 2010). f Cryoelectron microscopy (longitudinal slice) showing, from the inside out, cytoplasmic filaments (red line), cytoplasmic membrane (green line), lipoprotein layer (purple circles), peptidoglycan layer (tan line), flagellar filament (thick blue line), and outer membrane (green line). Bar, 50 nM. Reproduced with permission from reference (Liu et al. 2010). g [³H]palmitate-labeled lipids were extracted from isolated T. pallidum outer membranes and separated by two-dimensional thin layer chromatography. GL glycolipids; CL cardiolipin; PC phosphatidylcholine; PS phosphatidylserine; PG phosphatidylglycerol; O origin. Reproduced from reference (Radolf et al. 1995b)