Morphology of freeze-etched Treponema refringens (Nichols)

The freeze-etch technique was used to study the morphology of Treponema refringens (Nichols). There is a single band of cytoplasmic fibrils which follows a path in the form of a right-handed helix with a periodicity of 1500 nm around the body of the treponeme just below the cytoplasmic membrane. There are two major fracture planes, one located in the interior of the outer envelope and the second in the interior of the cytoplasmic membrane. The "blebs" or "surface protuberances", which are quite prominent in negative-stained preparations, were not evident with freeze-etch preparation, indicating they are not a part of the normal structure of this organism. The outer envelope in untreated cells was observed to closely fit the body of the treponeme, whereas the outer envelope of glutaraldehyde-treated cells had a loose, wrinkled appearance. Thus the "loose-fitting" outer envelope generally described for treponemes is most likely an artifact of preparation for negative-staining and thin-sectioning.