CONICET | Buscador de Institutos y Recursos Humanos

Integrons are classified according to their respective integrase genes. Class 2 integrons have been always described up to date as embedded in the Tn7 family of transposons. Tn7 is a specific and sophisticated mobile element which includes a defective class 2 integron and the transposition module formed by the tnsA, tnsB, tnsC, tnsD and tnsE genes. We studied the distribution of the transposition genes of Tn7 in two distant bacterial population, analyzing six hundred and sixty nine gram negative bacilli isolates (n=669) from clinical and environmental samples collected during the period 1998-2006 in Argentina. In this study we found that in some isolates there was no association between the transposition module and the class 2 integron integrase and vice versa. We found three isolates of Acinetobacter baumannii harboring only the class 2 integrase gene. On the other hand, three isolates (P. fluorescence, R. pickettii and S. algae) carrying only some of the tns genes were also found. In addition, new tnsA-like and tnsB-like genes in Shewanella algae and S. putresfaciens isolates were established. These results led us to search for all the class 2 integrase-like genes, the Tn7 and the Tn7-like transposition genes and their surrounding context described in the GenBank up to date. For that purpose, we carried out genetic analysis and comparative genomics using the Artemis software in order to elucidate the genomic rearrangements of Tn7 and Tn7-like elements. We found a huge variability of rearrangements among the sequences we analysed; these results resembled the variety of structures found in the isolates involved in our study. Our data evidenced that class 2 integrase genes do not always clustered with tns genes; this means that class 2 integrons are not always embedded in the Tn7 transposon as was previously thought.

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