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Genetic Characterization and Diversity of Rathayibacter toxicus

First, second, and third authors: Department of Plant Pathology, University of Nebraska, Lincoln; fourth author: Plant and Pest Science, University of Adelaide, Adelaide, SA, Australia; and fifth author: U.S. Department of Agriculture-Agricultural Research Service, Foreign Disease-Weed Science Research Unit, Ft. Detrick, MD

Rathayibacter toxicus is a nematode-vectored gram-positive bacterium responsible for a gumming disease of grasses and production of a highly potent animal and human toxin that is often fatal to livestock and has a history of occurring in unexpected circumstances. DNA of 22 strains of R. toxicus from Australia were characterized using amplified fragment length polymorphism (AFLP) and pulsed-field gel electrophoresis (PFGE). AFLP analysis grouped the 22 strains into three genetic clusters that correspond to their geographic origin. The mean similarity between the three clusters was 85 to 86%. PFGE analysis generated three different banding patterns that enabled typing the strains into three genotypic groups corresponding to the same AFLP clusters. The similarity coefficient was 63 to 81% for XbaI and 79 to 84% for SpeI. AFLP and PFGE analyses exhibited an analogous level of discriminatory power and produced congruent results. PFGE analysis indicated that the R. toxicus genome was represented by a single linear chromosome, estimated to be 2.214 to 2.301 Mb. No plasmids were detected.