MORPHOLOGY OF TREPONEMA MICRODENTIUM AS REVEALED BY ELECTRON MICROSCOPY OF ULTRATHIN SECTIONS

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 the 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.Spirochetes such as Treponema, Leptospira, and Borrelia form, in vitro or in vivo, spherical structures which have been designated as granules (3, 4, 7, 13), cysts (16, 20), and spherical forms (2). Several investigators have studied these structures by electron microscopy and have discussed their significance (6,8). With a few exceptions (3, 15), the information on human oral treponemes has been obtained from negatively stained or shadowed preparations.In a previous paper (21), we reported that the spherical body (SB) of oral spirochetes differed in size and formation rate from those observed by Hampp (7) and that the SB had a great affinity for oral spiroch etal cells. Because of its large size, our oral spirochete provided a model for studying the fine structure and biological characteristics of the SB. More precise morphological studies on SBs are 321

Section: Discussionsupporting

confidence: 83%

mentioning

confidence: 99%

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Electron Microscopy of the Spherical Body of Oral Spirochetes In Vitro: Further Studies

Umemoto¹,

Namikawa²

1980

“…Spirochetes are well known to be microorganisms forming morphologically abnormal structures both in vitro and in vivo. Under certain conditions these abnormal structures observed by electron microscopy have been shown to be the result of outerward expansion and/or development of the capsule as a limiting membrane which surrounds the axial flagella and main bodies of the organisms (1, 3,6).…”

mentioning

confidence: 99%

An Internal View of the Spherical Body of Treponema macrodentium as Revealed by Scanning Electron Microscopy

Umemoto

Namikawa

Yoshii

et al. 1982

The osmium-dimethyl sulfoxide-osmium method for clear visualization of intracellular structure was used to observe the detailed inner structure of the spherical bodies produced in vitro by a human oral treponeme. Scanning electron microscopy of the cracked spherical body revealed no morphological differences between the outer and inner surfaces of the spherical body membrane, and that multiple folded or somewhat linear main bodies adhere closely to the inner surface. In addition, axial flagella partially free from the main bodies spread widely within the body to make a network, and a number of blebs ranging from approximately I p.m to 0.2 p.m in diameter were located near the terminal or subterminal areas of the main bodies. The origin of the blebs and the mechanism of spherical body formation are discussed.Spirochetes are well known to be microorganisms forming morphologically abnormal structures both in vitro and in vivo. Under certain conditions these abnormal structures observed by electron microscopy have been shown to be the result of outerward expansion and/or development of the capsule as a limiting membrane which surrounds the axial flagella and main bodies of the organisms (1,3,6).Ultrathin sections of sperical bodies of a human oral spirochete, Treponema macrodentium strain G 7201, showed that the spherical body has a vacant space with some main bodies located close to the inner surface of the capsule (6). The outer surface structure of the spherical bodies has also been examined by scanning electron microscopy (7). However, no one has directly revealed the intrastructure of the abnormal spirochetal structures by scanning electron microscopy.Tanaka (4) recently developed a new method utilizing the osmium-dimethyl sulfoxide (DMSO)-osmium procedure for observation of the intracellular apparatus of some animal cells without any significant artifacts.In this paper we present the detailed internal structure of the spherical body produced in vitro by a human oral spirochete, as revealed by Tanaka's method.191

“…Helical cells of T. phagedenis biotype Reiter are converted into spherical forms by exposure to hypotonic conditions upon separation of the outer sheath from the protoplasmic cylinder (2). Similar spherical conversion of spirochetal cells is also found during the stationary growth phase of spirochetes (5,7). The conversion of helical cells into the spherical form may be caused by disintegration of the connective fibrils between the outer sheath and the wall-membrane complex followed by expansion of the outer sheath, because the protoplasmic cylinder still maintains a helical shape within the sperical form (1,7,11).…”

mentioning

confidence: 66%

Electron Microscopic Demonstration of Connective Fibrils between Outer Sheath and Wall‐Membrane Complex in Treponema phagedenis

Masuda

Kawata

1986

Spirochetes possess an outer sheath as an outermost membranous structure and their protoplasmic cylinder is covered by a wall-membrane complex (peptidoglycancytoplasmic membrane complex) (4). The wall-membrane complex, not the outer sheath, is considered to be the principal determinant of the helical shape specific for spirochetal cells, because the complex contains peptidoglycan (3-5). Therefore, we have assumed that the outer sheath must be connected with the wallmembrane complex by cellular substances (linkers) in order to form and maintain the helical appearance. This paper describes the presence of fibrils connecting the outer sheath and the wall-membrane complex as revealed by electron microscopy of thin sections of Treponem3 phagedenis.T. phagedenis biotypes Reiter and Kazan were grown anaerobically at 37 C in a modified Kawata's thioglycolate mediu'n as described previously (8). Cells harvested from a 5-day culture were washed once with cold 0.05 M phosphate buffered saline (pH 7.2) by centrifugation, fixed with 1 % Os04 and treated with 0.5 % uranyl acetate according to the method of Kellenberger et al (6). Thin sections were then prepared and stained with lead citrate as described previously (9). Specimens were examined with a Hitachi HU-11E electron microscope operating at 75 kV.Electron micrographs of thin sections of both biotypes of T. phagedenis showed that a triple-layered outer sheath about 10 nm in width is present as an outermost layer of the cells (Fig. 1). A wall-membrane complex immediately surrounds the protoplasmic cylinder.cross-sectioned cells flagella (axial filaments) could be observed as electron-dense spots about 30-40 nm in diameter in the space between the outer sheath and the wall-membrane complex.The most striking feature was the presence of fibrils by which the outer sheath was connected with the wall-membrane complex. The connective fibrils were observable as moderately electron-densely stained, fluffy filaments about 8-12 nm in thickness. The helical shape of spirochetal cells seems to be principally determined by the wall-membrane complex since it contains peptidoglycan (3-5). On the other hand, the outer sheath may not participate in forming the helical shape since it consists mainly of protein, phospholipid and carbohydrate and does not 183