ABSTRACTGenetic modifications of bacterial chromosomes are important for both fundamental and applied research. In this study, we developed an efficient, easy-to-use system for genetic modification of theEscherichia colichromosome, a two-plasmid method involving lambda Red (λ-Red) recombination and I-SceI cleavage. An intermediate strain is generated by integration of a resistance marker gene(s) and I-SceI recognition sites in or near the target gene locus, using λ-Red PCR targeting. The intermediate strain is transformed with a donor plasmid carrying the target gene fragment with the desired modification flanked by I-SceI recognition sites, together with a bifunctional helper plasmid for λ-Red recombination and I-SceI endonuclease. I-SceI cleavage of the chromosome and the donor plasmid allows λ-Red recombination between chromosomal breaks and linear double-stranded DNA from the donor plasmid. Genetic modifications are introduced into the chromosome, and the placement of the I-SceI sites determines the nature of the recombination and the modification. This method was successfully used forcadAknockout,gdhAknock-in, seamless deletion ofpepD, site-directed mutagenesis of the essentialmetKgene, and replacement ofmetKwith theRickettsiaS-adenosylmethionine transporter gene. This effective method can be used with both essential and nonessential gene modifications and will benefit basic and applied genetic research.
Highly Efficient Method for Introducing Successive Multiple Scarless Gene Deletions and Markerless Gene Insertions into the Yersinia pestis Chromosome