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Rearrangements in the staphylococcal beta-lactamase-encoding plasmid, pIP1066, including a DNA inversion that
A Derbise1, K G Dyke, N el Solh
1National Reference Centre for Staphylococci, Laboratoire des Staphylocoques et des Streptocoques, Institut Pasteur, Paris, France.
Abstract:
The plasmid plP1066, harboured by by a methicillin-resistant Staphylococcus aureus strain isolated in France, carries genes specifying beta-lactamase. This plasmid undergoes numerous rearrangements. One of these was insertion, between the genes binR and sin encoding resolvases, of a 16 kb element which displayed the characteristic features of a transposon. This putative transposon, named Tn5404, carried genes encoding proteins involved in its transposition, as well as a resolution system, which were indistinguishable from those of the S. aureus transposon Tn552. These were: p480 encoding a probable transposase, p271 encoding a putative ATP-binding protein, binL encoding a resolvase, and a resolution site, resL. In addition, Tn5404 carried aminoglycoside-resistance genes (aphA, str) and the insertion sequence IS1181. Tn5404 contained at its termini 116 bp imperfect inverted repeats, similar to those of Tn552, and was flanked by 6 bp direct repeats. Insertion of Tn5404 close to resR and to the structural and regulatory beta-lactamase genes (blaZ, blal, blaR1) of pIP1066, generated a 3.5 kb invertible segment flanked by inversely repeated resolution sites (resR, resL). This invertible segment, which carried p480, p271 and binL, generated in Tn552 or Tn5404, depending on its orientation. Thus, these two transposons share their transposition and resolution systems.
Insights
A novel transposon, Tn5404, was identified in methicillin-resistant Staphylococcus aureus. It shares transposition and resolution systems with Tn552, indicating a common mechanism for genetic rearrangement in bacteria.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Methicillin-resistant Staphylococcus aureus (MRSA) poses a significant public health threat.
- Plasmids play a crucial role in the dissemination of antibiotic resistance genes.
- Understanding mobile genetic elements like transposons is key to combating bacterial resistance.
Purpose of the Study:
- To characterize a novel transposon, Tn5404, identified in a French MRSA strain.
- To elucidate the genetic elements and mechanisms of transposition and resolution of Tn5404.
- To compare Tn5404 with other known Staphylococcus aureus transposons.
Main Methods:
- Plasmid DNA isolation and characterization.
- Gene sequencing and analysis of transposon elements.
- Comparative analysis of transposon sequences and genetic features.
Main Results:
- A 16 kb transposon, Tn5404, was identified on plasmid pIP1066, containing genes for transposition (p480, p271) and resolution (binL, resL).
- Tn5404 also carries aminoglycoside resistance genes (aphA, str) and insertion sequence IS1181.
- Tn5404 shares significant sequence and functional homology with the Staphylococcus aureus transposon Tn552, including terminal inverted repeats and flanking direct repeats.
- Insertion of Tn5404 created an invertible segment within the plasmid, demonstrating its role in genetic rearrangements.
Conclusions:
- Tn5404 is a novel transposon in MRSA with a distinct genetic makeup but shares core transposition and resolution machinery with Tn552.
- The findings highlight the dynamic nature of bacterial plasmids and the evolution of mobile genetic elements.
- This shared system suggests a common evolutionary origin or horizontal gene transfer of these mobile genetic elements in Staphylococcus aureus.