STRUCTURAL AND FUNCTIONAL-CHARACTERIZATION OF IS1358 FROM VIBRIO-CHOLERAE

The new epidemic serovar O139 of Vibrio cholerae has emerged from the pandemic serovar O1 biotype El Tor through the replacement of a 22-kbp DNA region by a 40-kbp O139-specific DNA fragment. This O139-specific DNA fragment contains an insertion sequence that was described previo usly (U. B. Stroeher, K. E. Jedani, B. K. Dredge, R. Morona, M. H. Bro wn, L. E. Karageorgos, J. M. Albert, and P. A. Manning, Proc. Natl. Ac ad. Sci. USA 92:10374-10378, 1995) and designated IS1358(O139). We stu died the distribution of the IS1358 element in strains from various se rovars by Southern analysis. Its presence was detected in strains from serovars O1, O2, O22, O139, and O155 but not in strains from serovars O15, O39, and O141. Furthermore, IS1358 was present in multiple copie s in strains from serovars O2, O22, and O155. We cloned and sequenced four copies of IS1358 from V. cholerae O22 and one copy from V. choler ae O155. A comparison of their nucleotide sequences with those of O1 a nd O139 showed that they were almost identical. We constructed a trans poson consisting of a kanamycin resistance gene flanked by two directl y oriented copies of IS1358 to study the functionality of this element . Transposition of this element from a nonmobilizable plasmid onto the conjugative plasmid pOX38-Gen was detected in an Escherichia coli rec A donor at a frequency of 1.2 x 10(-8). Sequence analysis revealed tha t IS1358 duplicates 10 bp at its insertion site.