FIG 7 .

Structure of T. pallidum subsp. pallidum Nichols following 54 days of in vitro culture, as determined by cryo-electron microscopy. (A and D) Two T. pallidum cells were imaged at low magnification (bar, 1 µm). (B, C, E, and F) Highlighted areas in panels A and D were imaged at high magnification (bar, 200 nm). B, intact region in the middle of the cell, showing the binding of small (~10-nm) particles or vesicles to the outer membrane surface; C, region of the cell in panel A in which the outer membrane has been stripped off. Note the lack of bound particles. E, end of the cell in panel D, showing the conical tip structure and a prominent membrane bleb, both typical of T. pallidum structure; F, intact region in middle of cell. The outlines of periplasmic flagella are clearly visible in this and other panels.