IS26 cannot move alone.

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• The insertion sequence IS26 is a significant factor in the spread of antibiotic resistance genes among Gram-negative bacteria.
• Understanding the transposition mechanism of IS26 is critical for combating antimicrobial resistance.

Purpose of the Study:

• To investigate whether the insertion sequence IS26 can transpose independently (simple transposition) or if it exclusively forms cointegrates.
• To elucidate the precise mechanism of IS26-mediated DNA integration.

Main Methods:

• Utilized two-step PCR with outward-facing primers to detect circular IS26 molecules.
• Employed Gibson assembly for cloning a synthetic IS26 construct with a chloramphenicol resistance gene.
• Assessed IS activity using a standard mating-out assay in a recA-Escherichia coli strain with a conjugative plasmid R388.

Main Results:

• Circular IS26 molecules, indicative of a copy-out transposition route, were not detected via PCR.
• The synthetic IS26 construct successfully integrated into the R388 plasmid, conferring chloramphenicol resistance.
• Analysis of transconjugants revealed that IS26::catA1 exclusively formed cointegrates, with no evidence of simple transposition or independent movement.

Conclusions:

• The IS26 transposase (Tnp26) exclusively mediates the formation of cointegrates, not simple transposition of IS26 alone.
• The findings clarify that IS26 does not move independently, and cointegrate formation is the sole outcome.
• This research reframes the understanding of complex resistance region formation, advising against invoking simple IS26 transposition.