Site-specific integration of the phage phi CTX genome into the Pseudomonas aeruginosa chromosome: characterization of the functional integrase gene located close to and upstream of attP.

The site-specific integration of the phage phi CTX genome, which carries the gene for a pore-forming cytotoxin, into the Pseudomonas aeruginosa chromosome was analysed. The 1,167 bp integrase gene, int, located immediately upstream of the attachment site, attP, was characterized using plasmid constructs, harbouring the integration functions, and serving as an integration probe in both P. aeruginosa and Escherichia coli. The attP plasmids p1000/p400 in the presence of the int plasmid pIBH and attP-int plasmids pINT/pINTS can be stably integrated into the P. aeruginosa chromosome. Successful recombination between the attP plasmid p1000 and the attB plasmid p5.1, in the presence of the int plasmid pIBH in E. coli HB101 showed that the int gene is active in trans in E. coli. The int gene product was detected as a 43 kDa protein in E. coli maxicells harbouring pINT. Proposed integration arm regions downstream of attP are not necessary for the integration process. pINT and phage phi CTX could be integrated together into P. aeruginosa chromosomal DNA, yielding double integrates.