title: An attachment tip and pili-like structures in insect- and plant-pathogenic spiroplasmas of the class Mollicutes.
abstract: Ultrastructural studies using scanning electron microscopy (SEM), negative-staining transmission electron microscopy (TEM), and thin-sectioning TEM on four species of Spiroplasma, in vitro and/or in vivo, indicated that their helices commonly possess one tapered end (tip structure) and one blunt or round end. These tip structures appeared morphologically different from the rest of the helix, exhibiting an electron-dense conical or rod-shaped core. In thin sections of the midgut of the leafhopper Dalbulus elimatus, the tip structures of Spiroplasma kunkelii in the midgut lumen were mostly aligned between microvilli, perpendicular to the apical plasma membrane of epithelial cells. These tip structures appeared frequently attached or closely apposed to the plasma membrane, in which cup-shaped invaginations close to the tips were observed. Pleomorphic forms of spiroplasma, enclosed in membranous vesicles, were found in the cytoplasm of the midgut epithelial cells. These findings suggest that the tip structure may be involved in the orientation and attachment of spiroplasma helices in relation to their host cells, and thus may be functionally comparable to the "attachment organelle" of mycoplasmas. Additionally, pili-like structures were observed by negative-staining TEM on the surface of Spiroplasma melliferum, and in thin sections of S. kunkelii infecting the leafhopper vector Dalbulus gelbus.
authors.affiliation: Department of Entomology, The Ohio State University, 1680 Madison Avenue, Ohio Agricultural Research and Development Center, Wooster, OH 44691, USA.
authors.forename: El-Desouky
authors.initials: el-D
authors.lastname: Ammar
authors.forename: Dave
authors.initials: D
authors.lastname: Fulton
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Bai
authors.forename: Tea
authors.initials: T
authors.lastname: Meulia
authors.forename: Saskia A
authors.initials: SA
authors.lastname: Hogenhout
mesh_terms: D000818:Animals; D001422:Bacterial Adhesion / Q000502:physiology*; D002462:Cell Membrane / Q000382:microbiology / Q000648:ultrastructure; D003593:Cytoplasm / Q000382:microbiology / Q000648:ultrastructure; D004847:Epithelial Cells / Q000382:microbiology / Q000648:ultrastructure; D010861:Fimbriae, Bacterial / Q000502:physiology* / Q000648:ultrastructure; D006430:Hemiptera / Q000382:microbiology; D008854:Microscopy, Electron; D008855:Microscopy, Electron, Scanning; D008867:Microtomy; D016624:Negative Staining; D013149:Spiroplasma / Q000502:physiology* / Q000648:ultrastructure*