Insertion-sequence-dependent rearrangements of Pseudomonas cepacia plasmid pTGL1

Pseudomonas cepacia 249 (ATCC 17616) harbors a 170-kilobase (kb) plasmid designated pTGL1. We identified three insertion sequences, IS405, IS408, and IS411, on this plasmid. Various prototrophic and auxotrophic derivatives in our collection contained variants of pTGL1 formed by accretion and deletion of other elements. Plasmid pTGL6, the variant in one prototroph, evolved from pTGL1 by the addition of three copies of IS401 (1.3 kb) and one of IS402 (1 kb), to generate pTGL5, and recombination between two of the copies of IS401 on pTGL5 to form pTGL6. The latter event entailed loss of one copy of IS401 and an additional 5.4 kb of plasmid DNA. Derivatives of the broad-host-range plasmid pRP1 carrying the above insertion sequences and recombinant plasmids carrying fragments of plasmids pTGL6 and pTGL5 were used as probes to ascertain the extent of reiteration of the various elements in the P. cepacia genome. The data indicate a high frequency of genomic rearrangements which presumably contributes to the extraordinary adaptability of this bacterium.