Marker-free chromosomal expression of foreign and native genes in Escherichia coli

Genetic manipulation of Escherichia coli strains for desired traits is the most applied strain engineering approach in industrial applications. For chromosomal insertion of genes and controlled expression of genomic genes in E. coli, the replicon-free and markerless method is described based on a series of conditional-replication plasmids called phage-integration vectors. They mainly carry the multiple cloning site and the prophage attachment site, which are sandwiched by two FRT sites. With the aid of the phage integrase from conditional-replication helper plasmids, the passenger genes of either foreign or native type incorporated into the integration vectors can be specifically integrated into bacterial genome at the prophage attachment site. Finally, the inserted DNA containing replicon and/or selective markers in integrants can be eliminated by the act of the FLP recombinase provided from a conditional-replication helper plasmid.