Caudovirales

Caudovirales is an order of tailed bacteriophages, viruses that infect bacteria. Members possess nonenveloped, double-stranded DNA genomes and a icosahedral capsid attached to a tail that serves to recognize hosts and inject the genome. Historically, Caudovirales has included three main families defined by tail morphology: Myoviridae, Siphoviridae, and Podoviridae.

Morphology and structure are used to differentiate members of Caudovirales. Myoviridae are characterized by long, contractile tails that drive genome injection; Siphoviridae have long, noncontractile tails; Podoviridae have short, noncontractile tails. The tails, often with complex baseplates and fibers, mediate attachment to bacterial receptors. Capsids are typically 50–100 nm in diameter, with genome enclosed within.

Genomes and replication: Caudovirales genomes are linear double-stranded DNA, usually ranging from about 18 to over 170 kilobases and encoding tens to hundreds of proteins. Replication occurs in the bacterial cytoplasm using host machinery, with assembly involving head and tail modules. Most members are lytic, producing new virions, while some can integrate into the host genome as prophages.

Ecology and applications: Caudovirales phages are the most abundant and diverse viruses in many environments, playing key roles in regulating bacterial populations and gene transfer. They are studied for phage therapy, biotechnology, and as tools in molecular biology.

Taxonomy: The order Caudovirales has long served as an umbrella for tailed dsDNA phages and is recognized in viral taxonomy by the ICTV. In recent years taxonomy has evolved with new family-level reorganizations, but the three traditional families remain widely cited as defining tail morphologies within the group.