An efficient, scarless, selection-free technology for phage engineering

Many phage engineering technologies, mainly based on the CRISPR-Cas system, have been recently developed. Here we present a method to genetically engineer the Escherichia coli phages T5, T7, and P1 by adapting a technology, called pORTMAGE, developed for engineering bacterial genomes. The technology comprises of E. coli harboring a plasmid encoding a potent recombinase and a gene transiently silencing a repair system. Oligonucleotides with the desired phage mutation are electroporated into E. coli followed by infection of the target bacteriophage. The high efficiency of this technology, ranging from 1-14% of desired recombinants, allows low-throughput screening for the desired mutant. We demonstrated the use of this technology for single-base substitutions, for deletions of 50 bases, for insertions of 20 bases, and for three different phages. The technology may be adjusted for use across many bacterial and phage strains. ### Competing Interest Statement The authors have declared no competing interest.