Dissemination of the Tn402 transposon family among bacterial genomes

CECILIA QUIROGA; PAULA M SCALZO; MARÍA PAULA QUIROGA; DANIELA CENTRÓN

Congreso; V Congreso de Microbiología General. SAMIGE.; 2008

The Tn402 transposon consists of four genes, tniA, B, Q and R. It has been first described in the IncP1 plasmid R751 from Enterobacter aerogenes, which carries a class 1 integron; however, only Tn402 derivatives were found spread among the clinical isolates. It has been previously reported that the Tn402 transposon was an ancient vehicle for the spread of resistance genes. In addition, the Tn5053/402 transposon family is also responsible of the dissemination of the mercury resistance due to the association of the transposition modul tni with the mer operon. Tn402 belong to the Tn5053/402 family of transposases that recongnize a relatively specific target, the res site. Most Tn5053/402 family members are located in plasmids that belong to the IncP-B1 incompatibility group helping in the horizontal transference of the transposon. The aim of this work is to understand the role of the Tn402 in the bacterial kingdom as well as to evaluate its presence in different niches. We searched for the TniR sequence protein from the Tn402 tranposon in complete (n = 736) and partial (n = 1181) bacterial genomes available in the GenBank. Only 30 genome encoded TniR with a sequence identity higher to 80%; but only 13 genomes also encoded for the TniA, TniB and TniQ proteins indicating that the tni module was complete and its dissemination is limited to a 1.3% of the bacterial genome. In parallel, we searched for the presence of the tniR and tniA genes in 98 environmental isolates recovered from low antropic environmental niches by the PCR technique using specific primers. Nineteen out of 98 (19.4%) harboured an identical copy of the tniR gene but only 3 also had the tniA gene indicating that 3.1% of the isolates had the transposon tni module. Six of 19 (31.6%) bacterial genomes had the mer operon associated to the transposon; similarly there was a 26% prevalence of the operon in the environmental samples indicating a global spread of the operon. Phylogenetic analysis based on the TniR sequence showed that the Tn5053/402 had two main lineages with no consistent pattern based on the procedence of the microorganism or the association to the antibiotic o mercury resistance. Our analysis also showed that while the TniR protein is widely encoded in different bacteria from very dissimilar niches, the tni module of the Tn5053/402 family is not. Since the Tn402 transposon has been always found disrupted at the tni module is it possible to assume that its survival in a bacterial genome is compromised.