Influence of osmotic pressure on the morphology of the Reiter treponeme.

Hardy, Paul H., Jr. (Johns Hopkins University, Baltimore, Md.) and E. Ellen Nell. Influence of osmotic pressure on the morphology of the Reiter treponeme. J. Bacteriol. 82: 967-978. 1961.-Spherical bodies similar to those that develop spontaneously in cultures of treponemes, and which have been considered by many investigators to represent one stage in a complex life cycle of these organisms, can be produced rapidly with the Reiter treponeme by merely altering the medium in which the organisms are suspended. Osmotic pressure appears to be the major factor responsible for this effect, as shown by the observation that treponemes suspended in NaCl solutions of 0.15 to 0.10 m retain their spirochetal morphology, whereas organisms suspended in more dilute salt solutions rapidly become spherical. Moreover, the concentration of salt appears to influence both the rate and extent of sphere formation. Further evidence that osmotic pressure is primarily involved is demonstrated by the selectivity of the conditions under which spheres form. Treponemes suspended in various 0.3 osmolal solutions either retain their spiral shape or form spheres, depending upon the nature of the solute. Viability studies of suspensions containing predominantly spherical forms, which have developed spontaneously or have been artificially induced, have failed to produce evidence that the resulting growth of treponemes came from the spheres. It is concluded, therefore, that the naturally occurring spheres probably arise as the result of an osmotic imbalance which develops between the cells and their environment, and that the spheres represent degenerative forms rather than an intermediate stage in a life cycle.