Siphoviruses exiting an infected bacterium, illustration. Siphoviridae are a family of bacteriophages with a double-stranded deoxyribonucleic acid (DNA) genome. They infect bacteria and archaea. Siphoviruses are non-enveloped with an icosahedral capsid (protein coat, red) head and a flexible, non-contractile tail (green). Siphoviruses exit from an infected bacterium through cell lysis.