Translocation of transposition-deficient (Tnd PKLH2-like) transposons in the natural environment: mechanistic insights from the study of adjacent DNA sequences

Abstract

A family of plasmid-borne DNA fragments of different length, apparently inherited from an ancient plasmid, has been identified in the world population of environmentalAcinetobacterstrains. These fragments, named PPFs (parentalplasmid DNAfragments), were ≥99·8 % identical to each other in the common regions, and contained in their central region a variant of an aberrant mercury-resistance transposon (Tn^dPKLH2) that has lost its transposition genes. As a rule, recombinogenic elements were found at the breakpoints of identity between the different PPFs. Of these recombinogenic elements, a newly identified IS6family element, a transposon, or a resolvase gene interrupted one end of the PPFs. At the opposite end, the breakpoint of some PPFs was mapped to the recombination point within, in each case, a different variant of aressite (RS2), whilst in other PPFs, this end was eroded by insertion of a newly identified IS6family element. On the basis of DNA sequence data, possible mechanisms of translocation of defective Tn^dPKLH2-like elements via recombination events implicating the nearbyres(resolution) site and IS element are proposed.