Growth phase of host Escherichia coli MG1655 influences T4 and T7 bacteriophage replication patterns during coinfection.

SUMMARY T4 and T7 bacteriophages are proposed to compete during coinfection of Escherichia coli, impacting their replication relative to monoinfection conditions. During monoinfection of E. coli, T4 has been suggested to replicate optimally in exponential phase cells, while T7 in stationary phase cells. Our study investigates whether similar replication patterns will be observed during the coinfection of T4 and T7 in E. coli MG1655 growing in either the early exponential and stationary growth phases. Phage replication was followed post-infection by quantitative real-time Polymerase Chain Reaction over six hour period. During coinfection, we observed that T4 achieves higher relative copy number in the early exponential phase. Although both phages have reduced copy number in the stationary phase, compared to exponential phase, T7 exhibits higher copy numbers compared to T4, suggesting that it replicates more effectively in later phases of growth. Our results indicate that competitive interactions between T4 and T7 bacteriophages are indeed impacted by the growth phase of the host cells.