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Etiology

Distribution and Partial Characterization of pCS1, a Highly Conserved Plasmid Present in Clavibacter michiganense subsp. sepedonicum. Bradley D. Mogen, Postdoctoral research associate, Departments of Biochemistry and Plant Pathology, North Dakota State University, Fargo 58105; Arland E. Oleson(2), Robert B. Sparks(3), Neil C. Gudmestad(4), and Gary A. Secor(5). (2)(3)Professor and assistant professor, respectively, Department of Biochemistry, North Dakota State University, Fargo 58105; (4)(5)Assistant professor and associate professor, respectively, Department of Plant Pathology, North Dakota State University, Fargo 58105. Phytopathology 78:1381-1386. Accepted for publication 22 June 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-1381.

Forty-nine strains of Clavibacter michiganense subsp. sepedonicum, (synonym Corynebacterium sepedonicum), the causal agent of potato bacterial ring rot, were screened for the presence of indigenous plasmids. Twenty-three of these strains contained a single plasmid with a molecular size of 50.6 ± 0.9 kb as determined by a combination of contour length measurements, comparison of electrophoretic mobility with intact plasmids of known molecular sizes, and summation of sizes of restriction fragments. Restriction digests and Southern hybridizations demonstrated that the plasmids from all positive strains were identical. The guanine plus cytosine content of this plasmid, designated pCS1, was determined to be 70.3%. Chromosomal DNA from the same C. m. sepedonicum strain had a guanine plus cytosine content of 72.4%. The plasmid copy number was found to be approximately 1.5 in strains that contain the autonomous form of pCS1. Southern hybridizations of chromosomal DNA from strains lacking the autonomous form of pCS1 revealed that all but one of the 26 tested strains contained the plasmid in integrated form. The extreme degree to which pCS1 has been conserved suggests that it encodes important, but unrecognized, metabolic functions.