Replicon fusions promoted by insertion sequences on Pseudomonas cepacia plasmid pTGL6.

Plasmid pMR5 (pRP1ts) failed to replicate in Pseudomonas cepacia at 47 degrees C. Selection at this temperature for maintenance of tetracycline resistance associated with this plasmid allowed isolation of cointegrate plasmids formed by fusion of pMR5 with pTGL6, a 170 kb plasmid harbored by P. cepacia 249. In the cointegrate plasmids pTGL100, pTGL101, and pTGL102, different regions of pTGL6 were involved in fusion with the same tra-2-containing region of pMR5. Formation of all three plasmids was promoted by insertion sequences on pTGL6, which were also represented in the chromosome. Two different copies of a 1.3 kb element, IS401, were involved in formation of pTGL100 and pTGL101. Another insertion sequence, IS402 (1 kb), promoted the fusion which formed pTGL102. Southern hybridization experiments indicated that each of the cointegrate plasmids contained an additional copy of the fusion mediating element. Plasmid pTGL100 was observed to resolve into two independent replicons: pTGL6 and pTGL105 (pMR5::IS401), a novel derivative of pMR5 containing a copy of IS401. The third cointegrate plasmid, pTGL102, evolved in two steps: fusion of pTGL6 and pMR5 mediated by IS402, and transposition of IS411 (1.9 kb) to a region of pMR5 distinct from that involved in the fusion. Plasmid pTGL6 contained one copy of IS402 and IS411 while pTGL102 contained two copies of each of these elements.