Electron microscopy of the spherical body of oral spirochetes in vitro. Further studies.

The surface and inner structure of the spherical bodies (SB) produced by the human oral treponeme strain G7201, similar to Treponema macrodentium, were studied by electron microscopy. Ultrathin sectioning and scanning techniques demonstrated that in the presence of a high concentration of sucrose, the outer envelope of one or both terminal ends of this oral spirochete changed into a swollen structure, the SB. Spirochetal cells adhered firmly to the surface of the resultant body. The membrane of the SB, i.e. the outer envelope, enclosed the coiled protoplasmic cylinder and five axial fibrils which were located between the envelope and th cylinder. Large expanded protoplasmic cylinders were observed, surrounded by a partially disrupted double membrane in some SBs. A number of frizzly fibrous structures, which differed from axial fibrils in number and shape, were also observed within these SBs. Except for abnormal or partially broken cylinders, the protoplasmic cylinders tended to be located close to the inner surface of the SB membrane, resulting in a central vacant space with occasional axial fibrils. These findings suggest that the oral spirochete produces an SB by terminal expansion of the outer envelope in the presence of high concentrations of sucrose. The outer envelope of the SB, which consists of two electron-dense layers, has the property of binding spirochetal cells to its outer layer and the protoplasmic cylinder and axial fibrils to the inner layer. Some protoplasmic cylinders were also observed to be swollen in the presence of high sucrose concentrations.