Bacteriophages (viruses that infect bacteria) are fascinating organisms that have played and continue to play a key role in bacterial genetics and molecular biology. Phage can confer key phenotypes on their host - for example, converting a non-pathogenic strain into a pathogen - and they play a key role in regulating bacterial populations in all sorts of environments. The phage-bacterium relationship varies enormously, from the simple predator-prey model to a complex, almost symbiotic relationship that promotes the survival and evolutionary success of both. While infection of bacteria used in...