Ecology, Structure, and Evolution of Phages.

Numerous bacteriophages-viruses of bacteria, also known as phages-have been described for hundreds of bacterial species. The Gram-negative species are close relatives of , yet relatively few previously described phages appear to exclusively infect this genus. Recent efforts to isolate phages have indicated these viruses are surprisingly abundant in the environment and have distinct genomic and structural properties. In addition, at least one model system used for experimental evolution studies has revealed a unique mechanism for developing faster infection cycles. Differences between these bacteriophages and other well-described model systems may mirror differences between their hosts' ecology and defense mechanisms. In this review, we discuss the history of phages and recent developments in their isolation and characterization and the structural information available for three model systems, Sf6, Sf14, and HRP29; we also provide an overview of potential selective pressures guiding both phage and host evolution.