CAVE system is a foundation of mutagenesis that can be used for both host-range increasing and enhancing characteristics of bacteria. This is done through selective mutation which is discussed slightly above. We use evolution and mutations and pick the best mutations for optimizing bacteriophages. This can be used for almost all features of bacteriophages. For example, using mutagenesis can allow a phage to possess the binding receptor of OMKO1 which can infect Pseudomonas aeruginosa using the outer membrane porin M (OprM) which is part of the antibiotic efflux pump.
This allows for mutagenesis to not just increase host-range, but also possess different inhibiting mechanisms against bacterial resistance mechanisms. This also applies for enzymes like dispersin B in the T7 phage which can deliver biofilm-degradation through the enzyme. The engineered phage T7 expressed DspB gene of Actinobacillus actinomycetemcomitans derived by T7 φ10 promoter, which can be recognized by T7 RNA polymerase, therefore can significantly reduce bacterial count in a single-species E. coli biofilm than the T7 phage control did. The same T7 was used to interfere with quorum sensing and inhibit biofilm formation, one of the primary resistance mechanisms.
The problem with this system however is that it is very difficult in many cases to identify desirable bacteriophages that can actually lyse a bacteria when infected. We feel that phage-derived enzymes directly from virion-associated lysins, endolysin, and deploymerace can be used to lyse bacteria and can be used with any phage through intraperitoneal inoculation. The benefit of this is that they can lyse a wide range of species rather than strains. Several studies have exploited the fact that host range is linked to tail fiber composition for some phages. One scientist Yoichi genetically modified a T2 phage by swapping the long tail fiber genes (gp37 and gp38) with those from phage PP01, which specifically targets E. coli O157:H7. The exchange was done by homologous recombination between the genome of phage T2 and a plasmid carrying two regions of homology, flanking the gp37 and gp38 genes of PP01. As DNA synthesis, sequencing, and genome engineering tech will become more efficient, it will significantly expedite the possible host range.
We can also use phages for phagemids which encode plasmids to target certain resistance genes like for targeting the aph-3 kanamycin resistance gene that was packaged in the Staphylococcal phage ΦNM. Phasmids have been used to transfer foreign DNA across several bacterial species that helped express genes for protective antigens for a variety of pathogens.
