Abstract
BackgroundThe lambda Red recombination system has been used to inactivate chromosomal genes in various bacteria and fungi. The procedure consists of electroporating a polymerase chain reaction (PCR) fragment containing antibiotic cassette flanked by homology regions to the target locus into a strain that can express the lambda Red proteins (Gam, Bet, Exo).ResultsHere a scarless gene modification strategy based on the Red recombination system has been developed to modify Pseudomonas genome DNA via sequential deletion of multiple targets. This process was mediated by plasmid pRKaraRed encoding the Red proteins regulated by PBAD promoter, which was functional in P. aeruginosa as well as in other bacteria. First the target gene was substituted for the sacB-bla cassette flanked by short homology regions (50 bp), and then this marker gene cassette could be replaced by the PCR fragment flanking itself, generating target-deleted genome without any remnants and no change happened to the surrounding region. Twenty genes involved in the synthesis and regulation pathways of the phenazine derivate, pyocyanin, were modified, including one single-point mutation and deletion of two large operons. The recombination efficiencies ranged from 88% to 98%. Multiple-gene modification was also achieved, generating a triple-gene deletion strain PCA (PAO1, ΔphzHΔphzMΔphzS), which could produce another phenazine derivate, phenazine-1-carboxylic acid (PCA), efficiently and exclusively.ConclusionsThis lambda Red-based technique can be used to generate scarless and sequential gene modification mutants of P. aeruginosa efficiently, using one-step PCR product flanked by short homology regions. Single-point mutation, scarless deletion of genes can be achieved easily in less than three days. This method may give a new way to construct genetically modified P. aeruginosa strains more efficiently and advance the regulatory network study of this organism.
Highlights
The lambda Red recombination system has been used to inactivate chromosomal genes in various bacteria and fungi
The backbone was originated from pDN18, in which the oriV and trfA regions were used to support the plasmid replication and stable maintenance in P. aeruginosa, oriT region was considered functional for the conjugal transfer among any gram-negative bacterial host virtually and tetA was a tetracycline resistance gene [18,19,20]
The PBAD promoter was used to regulate the expression of lambda Red proteins (Gam, Bet, Exo)
Summary
The lambda Red recombination system has been used to inactivate chromosomal genes in various bacteria and fungi. One of the most common approaches is sequence-specific deletion or insertion of the target genes or DNA fragments, and various methods have been developed based on the RecA-independent homologous recombination, such as RecET and lambda Red recombination system [4,5,6,7,8]. In these recombination events, selection markers, usually antibiotic markers are. These methods can not generate the true “scarless” mutants
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