On the stability of sequences inserted into viral genomes

Willemsen, Anouk; Zwart, Mark P

Bacteriophages were instrumental in the development of molecular cloning methods. Among dsDNA phages, lambdaviruses of E.coli were widely used as cloning vectors, and methods were developed to increase the stability and maximum size of inserts (Chauthaiwale, Therwath, and Deshpande 1992) . One interesting approach made use of the fact that there is a minimum genome size for efficient packaging into virus particles. When endogenous genes that are non-essential for the lytic cycle are removed, not only can larger sequences be inserted, but there is also selection for maintaining the inserted sequences because they increase genome size and enable packaging (Thomas, Cameron, and Davis 1974) . Moreover, it has been shown that phage T7 engineered with a biofilm-degrading enzyme (dispersin B) was superior to unmodified phage at clearing short-term biofilms (Lu and Collins 2007) . Although providing a 'public' benefit in the form of an exoenzyme that can degrade host defenses, surprisingly this insertion does not have a cost and is therefore stable (Schmerer et al. 2014) . Interestingly, the insertion of an endosialidase at the same locus was both beneficial and costly, although in this case evolutionary stability was not determined (Gladstone, Molineux, and Bull 2012) .