Mini-Tn7 insertion in bacteria with single attTn7 sites: example Pseudomonas aeruginosa

Broad host-range mini-Tn7 vectors facilitate integration of single-copy genes into bacterial chromosomes at a neutral, naturally evolved site. Here we present a protocol for employing the mini-Tn7 system in bacteria with single attTn7 sites, using the example Pseudomonas aeruginosa. The procedure involves, first, cloning of the genes of interest into an appropriate mini-Tn7 vector; second, co-transfer of the recombinant mini-Tn7 vector and a helper plasmid encoding the Tn7 site-specific transposition pathway into P. aeruginosa by either transformation or conjugation, followed by selection of insertion-containing strains; third, PCR verification of mini-Tn7 insertions; and last, optional Flp-mediated excision of the antibiotic-resistance selection marker present on the chromosomally integrated mini-Tn7 element. From start to verification of the insertion events, the procedure takes as little as 4 d and is very efficient, yielding several thousand transformants per microgram of input DNA or conjugation mixture. In contrast to existing chromosome integration systems, which are mostly based on species-specific phage or more-or-less randomly integrating transposons, the mini-Tn7 system is characterized by its ready adaptability to various bacterial hosts, its site specificity and its efficiency. Vectors have been developed for gene complementation, construction of gene fusions, regulated gene expression and reporter gene tagging.