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Cytology and Histology

Fimbriae of Phytopathogenic and Symbiotic Bacteria. Willem P. C. Stemmer, Research assistant, Department of Plant Pathology, University of Wisconsin, Madison 53706; Luis Sequeira, Professor, Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 77:1633-1639. Accepted for publication 17 June 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-1633.

Fimbriae are proteinaceous, filiform appendages on the bacterial cell surface that are thought to be important in attachment of bacteria to plant and other surfaces. We report here that fimbriae are common in many genera and species of plant pathogenic bacteria. Seventy-seven strains, including all genera and many species of plant pathogenic bacteria, were grown under appropriate cultural conditions and then examined for the presence of fimbriae by electron microscopy. Fimbriae were detected for the first time in Pseudomonas syringae pv. glycinea and pv. syringae, P. savastanoi (one strain each), and in Agrobacterium tumefaciens (14 strains). The presence of fimbriae was also confirmed for Rhizobium (Bradyrhizobium) japonicum (one strain), R. trifolii (three strains), R. leguminosarum (five strains), and P. solanacearum (five strains). Conditions under which fimbriae were produced most abundantly (shallow, static, aerobic cultures) were similar to those reported as most suitable for the production of fimbriae by mammalian pathogens. A detailed study of the fimbriae of P. solanacearum B1, an avirulent derivative of strain K60, was made. B1 cells are strongly fimbriated, whereas K60 cells are almost devoid of fimbriae. A new procedure for purification of B1 fimbriae was developed, consisting of precipitating them from the culture supernatant with 20% ammonium sulfate, followed by repeated sonication and washing with 0.5% sodium deoxycholate and 6 M urea. The fimbrial subunit is composed of a single protein with a molecular weight of about 9,500.