Described herein is a method of preparing an unbiased library of phage variants, comprising (a) preparing a population of “acceptor phage”; (b) removing an endogenous target gene and inserting gene variants into the acceptor phage genomes; (c) enriching the recombined phages; and (d) expressing the library for selection. The acceptor phage is a lytic phage comprising a synthetic genome wherein the target gene of interest is flanked by recombinase sites. The acceptor phage infects a first host bacteria expressing a recombination plasmid facilitating recombination. The phages then infect a second host bacteria expressing a counterselection system that accumulates recombined phage variants and selecting against non-recombined phages. The accumulated phage variants infect a third host bacteria. The phage library may then be sequenced and characterized.

Described herein is a method of preparing an unbiased library of phage variants, comprising (a) preparing a population of acceptor phage; (b) removing an endogenous target gene and inserting gene variants into the acceptor phage genomes; (c) enriching the recombined phages; and (d) expressing the library for selection. The acceptor phage is a lytic phage comprising a synthetic genome wherein the target gene of interest is flanked by recombinase sites. The acceptor phage infects a first host bacteria expressing a recombination plasmid facilitating recombination. The phages then infect a second host bacteria expressing a counterselection system that accumulates recombined phage variants and selecting against non-recombined phages. The accumulated phage variants infect a third host bacteria. The phage library may then be sequenced and characterized.

Described herein is a method of preparing an unbiased library of phage variants, comprising (a) preparing a population of acceptor phage; (b) removing an endogenous target gene and inserting gene variants into the acceptor phage genomes; (c) enriching the recombined phages; and (d) expressing the library for selection. The acceptor phage is a lytic phage comprising a synthetic genome wherein the target gene of interest is flanked by recombinase sites. The acceptor phage infects a first host bacteria expressing a recombination plasmid facilitating recombination. The phages then infect a second host bacteria expressing a counterselection system that accumulates recombined phage variants and selecting against non-recombined phages. The accumulated phage variants infect a third host bacteria. The phage library may then be sequenced and characterized.

Genetically modified phages are provided. Accordingly, there is provided a genetically modified phage comprising a polynucleotide encoding an anti-defense system polypeptide. Also provided are methods of producing and using same.

Provided is a bacteria-targeting capsid particle that is non-proliferative and has a high bactericidal effect. A capsid protein of a bacteriophage is prepared by a capsid nucleic acid element that synthesizes the capsid, which is divided from the bacteriophage genome and does not include a packaging region, but mainly includes the virion region. A bacteria-targeting capsid particle element (Bacteria-targeting capsid particle, B-CAP) is divided from a part of the bacteriophage genome other than the capsid nucleic acid element and includes a nucleic acid injection region, a replication region necessary for nucleic acid replication, and a packaging region. Although the assembled bacteria-targeting capsid particle (B-CAP) is non-proliferative, it can carry long DNA strands that give them new biological functions, such as bactericidal effects, or the other biological functions.