VIEW ARTICLE

Physiology and Biochemistry

Isolation and Characterization of Inner and Outer Membranes of Xanthomonas campestris pv. campestris. J. C. Dianese, Department of Plant Pathology, University of Georgia, Georgia Experiment Station, Experiment 30212, Present address: Departamento de Biologia Vegetal, Universidade de Brasilia, Brasilia, DF, Brasil, 70.910; N. W. Schaad, Department of Plant Pathology, University of Georgia, Georgia Experiment Station, Experiment 30212, Present address: Department of Plant and Soil Science, University of Idaho, Moscow 83843. Phytopathology 72:1284-1289. Accepted for publication 10 March 1982. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-1284.

Cell envelopes of Xanthomonas campestris pv. campestris were extracted by conventional methods and characterized. The total membrane fraction was resolved into a light (L), intermediate (M), and two heavy (H₁ and H₂) fractions by 45–70% sucrose step density gradient centrifugation. The L fraction contained 67% of the succinate dehydrogenase (SDH) activity, whereas the H₁ and H₂ fractions contained 69% of the 2-keto-deoxyoctonate (KDO). Most remaining SDH (18%) and KDO (25%) was in the M fraction. Xanthomonadin, a brominated arylopolyene pigment, was located exclusively in fractions H₁ and H₂. Based on these data, fractions L and H₁ plus H₂ were considered to be primarily compounds from the inner and outer membranes, respectively. The relative phospholipid content of the inner membrane was considerably higher than that of the outer membrane. Six phospholipids were identified; the bulk (about 20% each) of these were lysophosphatidylethanolamine, phosphatidylethanolamine, and phosphatidylserine. Electron micrographs showed the inner membrane to consist of circular unit membranes much smaller than the larger elongated structures of the outer membrane. Approximately 30 polypeptides in the total membrane fraction were resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Three major polypeptides (44, 26, and 23 kilodaltons) were resolved in the outer membrane fraction. The possible importance of membrane proteins in the pathogenicity of X. campestris is discussed.