A Positive Strain Identification Method for Rhizobium meliloti

About 80% of Rhizobium meliloti strains contain 1 to 11 copies of insertion sequence ISRm1 in their genomes (R. Wheatcroft and R. J. Watson, J. Gen. Microbiol. 134:113-121, 1988). Hybridization to separated genomic DNA fragments with an ISRm1-specific probe produces patterns of hybridization bands which are distinctive for each strain. These patterns can be compared between strains to prove or disprove common identity. In most cases relatedness can be inferred despite phenotypic differences or minor genomic alterations.