Cryo-Electron Tomography Elucidates the Molecular Architecture of Treponema pallidum, the Syphilis Spirochete

Authors

Jacques Izard, The Forsyth Institute & New York State Department of HealthFollow
Christian Renken, University of Connecticut Health Center
Chyong-Ere Hsieh, University of Connecticut Health Center
Daniel C. Desrosiers, University of Connecticut Health Center
Star Dunham-Ems, University of Connecticut Health Center
Carson La Vake, University of Connecticut Health Center
Linda L. Gebhardt, University of Connecticut Health Center
Ronald J. Limberger, University of Connecticut Health Center
David L. Cox, Centers for Disease Control and Prevention
Michael Marko, University of Connecticut Health Center
Justin D. Radolf, University of Connecticut Health CenterFollow

Date of this Version

10-3-2009

Citation

2009, American Society for Microbiology. All Rights Reserved

Comments

JOURNAL OF BACTERIOLOGY, Dec. 2009, p. 7566–7580 Vol. 191, No. 24 0021-9193/09/$12.00 doi:10.1128/JB.01031-09

Abstract

Cryo-electron tomography (CET) was used to examine the native cellular organization of Treponema pallidum, the syphilis spirochete. T. pallidum cells appeared to form flat waves, did not contain an outer coat and, except for bulges over the basal bodies and widening in the vicinity of flagellar filaments, displayed a uniform periplasmic space. Although the outer membrane (OM) generally was smooth in contour, OM extrusions and blebs frequently were observed, highlighting the structure’s fluidity and lack of attachment to underlying periplasmic constituents. Cytoplasmic filaments converged from their attachment points opposite the basal bodies to form arrays that ran roughly parallel to the flagellar filaments along the inner surface of the cytoplasmic membrane (CM). Motile treponemes stably attached to rabbit epithelial cells predominantly via their tips. CET revealed that T. pallidum cell ends have a complex morphology and assume at least four distinct morphotypes. Images of dividing treponemes and organisms shedding cell envelope-derived blebs provided evidence for the spirochete’s complex membrane biology. In the regions without flagellar filaments, peptidoglycan (PG) was visualized as a thin layer that divided the periplasmic space into zones of higher and lower electron densities adjacent to the CM and OM, respectively. Flagellar filaments were observed overlying the PG layer, while image modeling placed the PG-basal body contact site in the vicinity of the stator–P-collar junction. Bioinformatics and homology modeling indicated that the MotB proteins of T. pallidum, Treponema denticola, and Borrelia burgdorferi have membrane topologies and PG binding sites highly similar to those of their well-characterized Escherichia coli and Helicobacter pylori orthologs. Collectively, our results help to clarify fundamental differences in cell envelope ultrastructure between spirochetes and gram-negative bacteria. They also confirm that PG stabilizes the flagellar motor and enable us to propose that in most spirochetes motility results from rotation of the flagellar filaments against the PG.