I‐ Ceu I fragment analysis of the Shigella species: evidence for large‐scale chromosome rearrangement in S. dysenteriae and S. flexneri

I‐ Ceu I fragments of four Shigella species were analyzed to investigate their taxonomic distance from Escherichia coli and to collect substantiated evidence of their genetic relatedness because their ribosomal RNA sequences and similarity values of their chromosomal DNA/DNA hybridization had proved their taxonomic identity. I‐ Ceu I digestion of genomic DNAs yielded seven fragments in every species, indicating that all the Shigella species contained seven sets of ribosome RNA operons. To determine the fragment identities, seven genes were selected from each I‐ Ceu I fragment of E. coli strain K‐12 and used as hybridization probes. Among the four Shigella species, S. boydii and S. sonnei showed hybridization patterns similar to those observed for E. coli strains; each gene probe hybridized to the I‐ Ceu I fragments with sizes similar to that of the corresponding E. coli fragment. In contrast, S. dysenteriae and S. flexneri showed distinct patterns; rcs F and rbs R genes that located on different I‐ Ceu I fragments in E. coli , fragments D and E, were found to co‐locate on a fragment. Further analysis using an additional three genes that located on fragment D in K‐12 revealed that some chromosome rearrangements involving the fragments corresponding to fragments D and E of K‐12 took place in S. dysenteriae and S. flexneri .