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Klebsiella pneumoniae 287-w carries three small narrow host range ( NHR) plasmids ( pIGMS31, pIGMS32, and pIGRK), which could be maintained in several closely related species of G ammaproteobacteria, but not in A lphaproteobacteria. The plasmids contain different mobilization systems ( MOB), whose activity in E scherichia coli was demonstrated in the presence of the helper transfer system originating from plasmid RK2. The MOBs of pIGMS31 and pIGMS32 are highly conserved in many bacterial plasmids (members of the MOB family), while the predicted MOB of pIGRK has a unique structure, encoding a protein similar to phage-related integrases. The MOBs of pIGMS31 and pIGMS32 enabled the transfer of heterologous replicons from E . coli into both gammaproteobacterial and alphaproteobacterial hosts, which suggests that these NHR plasmids contain broad host range MOB systems. Such plasmids therefore represent efficient carrier molecules, which may act as natural suicide vectors promoting the spread of diverse genetic information (including other types of mobile elements, e.g. resistance transposons) among evolutionarily distinct bacterial species. Thus, mobilizable NHR plasmids may play a much more important role in horizontal gene transfer than previously thought. [ABSTRACT FROM AUTHOR]

A sacB-based trap plasmid was used to clone a mosaic transposable element (TE) in the carotenoid producer Paracoccus marcusii OS22. This element is composed of an insertion sequence (IS) IS Pmar4 (IS As1 family), which contains an inserted functional transposable module (TMo) generated by a copy of IS 1247a (of the IS 1380 family). Besides IS 1247a sequences, the TMo also contains the 3′-end region of a putative α/β hydrolase gene, whose expression might be activated from the P2 promoter of IS 1247a. The identification of this novel TE provides evidence that transposition of TMos may change an IS into a more complex element resembling noncomposite transposons. [ABSTRACT FROM AUTHOR]