ABSTRACT
As discussed throughout this book, bacteriophages are viruses that only infect bacteria. They are like complex spaceships (Fig. 1), each carrying its genome from one susceptible bacterial cell to another in which it can direct the production of more phages. Each phage particle (virion) contains its nucleic acid genome (DNA or RNA) enclosed in a protein or lipoprotein coat, or capsid; the combined nucleic acid and capsid form the nucleocapsid. The target host for each phage is a specific group of bacteria. This group is often some subset of one species,1 but several related species can sometimes be infected by the same phage.
