PRD1 bacteriophage, illustration. Molecular model of the structure of a PRD1 bacteriophage. Bacteriophages are viruses that infect bacteria. The PRD1 bacteriophage is from the tectiviridae family, and infects gram-negative enterobacteria (for example, Escherichia coli). It has a structure similar to adenoviruses, with an icosahedral protein coat (capsid, dark blue), surrounding an internal membrane (purple). This encloses its linear double-stranded deoxyribonucleic acid (DNA, light blue) viral genome.