Treponema: Current ResearchThe Treponema are anaerobic, host-associated spirochetes that represent one of nine spirochetal genera of the phylum Spirochaetes as based on 16S rRNA sequence analysis. There is no other disease that has captured our imagination and creativity more than syphilis. Beginning with the historical lore of its origins, to its numerous and suggestive common names, and the notable historical personages who were thought to be afflicted with the "Great Pox," syphilis has always been close to the human psyche. Venereal syphilis was first reported as a new disease in Italy at the end of the 15th century, during the time of Spanish exploration and colonization of the American continent. Thus, many experts believe that this disease, and its causative organism Treponema pallidum, sailed from the Americas to Europe. There is anatomical and molecular fossil evidence supporting the existence of treponemal infections among native Americans in the pre-Columbian period, and perhaps more compelling, such evidence is scant among Europeans for the same period of time. Increasingly more specific and sensitive molecular probes may resolve this historical puzzle conclusively.
The recent sequencing of the genomes of several spirochetes permits a thorough analysis of the similarities and differences within this bacterial phylum. Treponema pallidum subsp. pallidum has one of the smallest bacterial genomes at 1.14 million base pairs (Mb) and has limited metabolic capabilities, reflecting its adaptation through genome reduction to the rich environment of mammalian tissue.
Treponema denticola and Treponema phagedenis are important models for deciphering the unique architectural and genetic features of treponemes. Darkfield and electron microscopy have delineated the general structure of treponemes as deduced from these two dimensional techniques. Advances in genetic tools and three dimensional visualization techniques are now linking cell architecture, cell ultrastructures, and genetic data. Ultrastructures are multi-component assemblies within the cell that drive specific functions critical to the cell such as cell division, cell shape and motility. A key treponemal ultrastructure is the cytoplasmic filament ribbon which is involved in the cell division process. Recently, application of new methods to the structural analysis of T. phagedenis has revealed novel features of the cytoplasmic filament ribbon. The observed cytoplasmic filament ribbon actually consists of independent filaments connected to each other via bridging components and anchored to the inner membrane. The nature and components of this macromolecular complex are discussed as well as the novelty of the filamentous ribbon structure. The availability of whole genome sequences from two treponemal species also allows the comparative study with other bacterial cytoskeleton-associated structures towards achieving a global picture of spirochetal cell biology.
Understanding the motility of Treponema species is still at its infancy. An analysis of motility mutants indicate that the periplasmic flagella, which are situated between the outer membrane sheath and cell cylinder, are directly involved in the motility in both Treponema denticola and Treponema phagedenis. Furthermore, not only do these organelles rotate in a manner similar to the flagella of rod-shaped bacteria, but they also have a skeletal function, i.e., they influence the shape of the cell of both species.
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