Characterization of <Emphasis Type="Italic">Agrobacterium</Emphasis> species by capillary isoelectric focusing

Tumorigenic and non-tumorigenic strains of Agrobacterium tumefaciens, A. rhizogenes, A.rubi, and A.vitis were examined using capillary isoelectric focusing, phenotypic determinative tests, PCR and fatty acid analysis. The isoelectric points (pI) of the 40 strains investigated clearly differentiated the strains according to their respective species. The different species were characterized with the following pI values: A. tumefaciens 2.2, A. rhizogenes 4.0, A. rubi 2.15, and A. vitis 2.6. This differentiation corresponded to the phenotypic, PCR and fatty acid characterizations. Strains with the similar chromosomal background but different plasmid content, e.g. A.vitis strain S4, and F2/5 gave the same pI values. Strains of Rhizobium species differed from Agrobacterium strains in their pI values. The advantage of capillary isoelectric focusing over the phenotypic determinative tests, PCR and fatty acid analysis is its speed (15 min), relative simplicity, and the very small amount of chemicals used. This rapid and simple method is a major improvement over the classical methods of separation of Agrobacterium species and should prove useful for rapid characterization of Agrobacterium-like colonies isolated from plant tumours for epidemiological and generic diversity studies.