Miniature Transposable Sequences Are Frequently Mobilized in the Bacterial Plant Pathogen Pseudomonas syringae pv. phaseolicola

Abstract

Mobile genetic elements are widespread in Pseudomonas syringae, and often associate with virulence genes. Genome reannotation of the model bean pathogen P. syringae pv. phaseolicola 1448A identified seventeen types of insertion sequences and two miniature inverted-repeat transposable elements (MITEs) with a biased distribution, representing 2.8% of the chromosome, 25.8% of the 132-kb virulence plasmid and 2.7% of the 52-kb plasmid. Employing an entrapment vector containing sacB, we estimated that transposition frequency oscillated between 2.6×10−5 and 1.1×10−6, depending on the clone, although it was stable for each clone after consecutive transfers in culture media. Transposition frequency was similar for bacteria grown in rich or minimal media, and from cells recovered from compatible and incompatible plant hosts, indicating that growth conditions do not influence transposition in strain 1448A. Most of the entrapped insertions contained a full-length IS801 element, with the remaining insertions corresponding to sequences smaller than any transposable element identified in strain 1448A, and collectively identified as miniature sequences. From these, fragments of 229, 360 and 679-nt of the right end of IS801 ended in a consensus tetranucleotide and likely resulted from one-ended transposition of IS801. An average 0.7% of the insertions analyzed consisted of IS801 carrying a fragment of variable size from gene PSPPH_0008/PSPPH_0017, showing that IS801 can mobilize DNA in vivo. Retrospective analysis of complete plasmids and genomes of P. syringae suggests, however, that most fragments of IS801 are likely the result of reorganizations rather than one-ended transpositions, and that this element might preferentially contribute to genome flexibility by generating homologous regions of recombination. A further miniature sequence previously found to affect host range specificity and virulence, designated MITEPsy1 (100-nt), represented an average 2.4% of the total number of insertions entrapped in sacB, demonstrating for the first time the mobilization of a MITE in bacteria.

Detection and Characterization of Miniature Inverted-Repeat Transposable Elements in "Candidatus Liberibacter asiaticus"

“…MITEs were first described in Neisseria sp. (4) and are now reported in many other bacteria (5)(6)(7)(8)(9)(10)(11)(12)(13)(14).…”

Bacterial Genome Instability

“…MITEs are widespread in eukaryotic genomes, where they can achieve high transposition activity using transposases encoded by other autonomous elements (36). Mobilization of MITEs has also been shown in bacteria (37). The study of MITEs in prokaryotes began recently, and they have not yet been well defined.…”

Historical and Epistemological Perspectives on What Horizontal Gene Transfer Mechanisms Contribute to Our Understanding of Evolution

“…Especially mammalian genomes, including human genomes, contain many retrotransposable LINE and SINE elements (Deininger and Batzer 2002). Some SINEs today are also classified as miniature inverted-repeat transposable elements (MITEs) (Bardaji et al 2011;Zhang et al 2000), which are especially numerous in flowering plants, but they are also found in insects and animals.…”