TRANSPOSON TN5403, A MOBILIZATION-HELPER ELEMENT - COMPLETE NUCLEOTIDE-SEQUENCE AND DISTRIBUTION IN AQUATIC STRAINS

Tn5403, a new transposable element, was found in a Klebsiella pneumoni ae strain (KIIIA) isolated from an aquatic environment following a pol lution accident. It was identified by its ability to mobilize oriT-del eted recombinant plasmids and thus can be proposed as a 'helper' eleme nt participating in the transfer mechanisms of non-conjugative plasmid s. Nucleotides sequence analysis shows that the element consists of 36 63 bp. Two open reading frames (ORFs) are found: one (tnpA) encoding a putative transposase and the other (tnpR) a putative resolvase. The t wo ORFs are transcribed in opposite directions and are separated by a putative recombination site (res). Results obtained with a specific pr obe suggest that Tn5403 or a similar element is present in different E nterobacteriaceae strains isolated from the same river three years aft er the isolation of the Tn5403-harbouring KIIIA strain.