Selecting for lysis in a temperate phage population

Temperate phages represent an abundant source of phage diversity, but their capacity for lysogeny limits their therapeutic potential. Here, we asked whether repeated selection for lytic replication could drive a temperate phage toward an obligately lytic lifestyle. We serially propagated a cocktail of three temperate coliphages using a modified Appelmans protocol in which phage populations were independently passaged on eight E. coli hosts. Whole-genome sequencing revealed substantial changes in population composition and mutation frequencies. The Uetakevirus phage 1362 was undetectable after the first round, whereas the closely related P2-like phages in the cocktail dominated the evolving populations. Mutations repeatedly accumulated in lysis- and lysogeny-associated genes. Longitudinal genomic analysis revealed rapid fixation of mutations in the integrase coding region, while variants in lysA, lysB, and holin increased in frequency over successive rounds of selection. Protein structure modeling localized selected mutations to regions with potential functional significance. These include the DNA-binding domain of integrase and a surface-exposed region of LysA. Together, these results show that sustained selection for lytic replication can drive rapid and repeatable genomic adaptation in temperate phage populations.