Dissemination of novel Tn family transposons carrying genes for synthesis and uptake of fimsbactin siderophores among isolates.

is a successful opportunistic pathogen that can compete for iron under iron-limiting conditions. Here, large novel transposons that carry genes for synthesis and transport of the fimsbactin siderophores present in some strains were examined. Tn, originally found in the global clone 1 (GC1) lineage 2 isolate D36, includes genes encoding proteins related to the TnsA, TnsB, TnsC transposition proteins (50-59 % identity), TnsD targeting protein (43 % identity) and TnsE (31 % identity) of Tn, and is found in the chromosome downstream of the gene, the preferred location for Tn, flanked by a 5 bp target site duplication. Tn is bounded by 29 bp inverted repeats and, like Tn, includes additional TnsB binding sites at each end. Tn or minor variants were detected in the equivalent location in complete or draft genomes of several further isolates belonging to GC1 [sequence type (ST) 1, ST81, ST94, ST328, ST623, ST717], GC2 (ST2) and ST10. However, in some of these isolates the surrounding region was clearly derived from a different lineage, indicating that the transposon may have been acquired by replacement of a segment of the chromosome. A recombination-free phylogeny revealed that there were several transposon acquisition events in GC1. The GC1 isolates were mainly lineage 2, but a potential third lineage was also detected. A related transposon, designated Tn, was detected in ATCC 17978 (ST437) and other ST437 isolates. However, the Tn targeting gene was interrupted by an ISAba12, and Tn is not downstream of .