Bacteriophages: Tailed

Abstract

Tailed bacteriophages are a widely distributed order of viruses that infect bacteria and Archaea. They all have a double‐stranded deoxyribonucleic acid (DNA) chromosome that is protected by an icosahedral capsid with a tail attached to one vertex. The tail is a specialised organelle that recognises the host and transfers the phage chromosome from inside the capsid to the host cytoplasm. Tails exhibit diverse morphologies that are divided into the three main classes: (1) short, (2) long and flexible and (3) long and contractile, that are used to define the three families of phage. The DNA‐filled capsids are icosahedral in shape, come in a range of sizes and are sometimes elongated along the tail axis. During infection, a phage may immediately take over the host to make new virions and lyse the cell (lytic cycle), or it may enter a dormant state, often by integrating its genome into the host genome (lysogenic cycle). Key Concepts Tailed bacteriophages are widespread in nature, but quite variable in size, shape and genetic content. During infection, phages may deliver both their DNA chromosome and proteins into the infected cell in order to take over the cell and replicate. Phage DNA replication mechanisms vary widely, but they usually make a large molecule that contains multiple copies of the phage genome that is used for packaging. New phage particles are built using separate assembly pathways for capsids, tails and tail fibers. Capsids are built as empty precursors using a scaffold that is discarded and tails are only added after the capsids are filled with DNA. Tailed bacteriophages very likely evolved from a common ancestor.