Introduction

Taxonomic Structure of the Family

Family	Myoviridae
Genus	“T4-like Viruses”
Genus	“P1-like Viruses”
Genus	“P2-like Viruses”
Genus	“Mu-like Viruses”
Genus	“SPO1-like Viruses”
Genus	“H-like Viruses”

Distinguishing Features

Tails are contractile, more or less rigid, long and relatively thick (80-455 16-20  nm). They consist of a central core built of stacked rings of 6 subunits and surrounded by a helical contractile sheath, which is separated from the head by a neck. During contraction, sheath subunits slide over each other and the sheath becomes shorter and thicker. This brings the tail core in contact with the bacterial plasma membrane and is an essential stage of infection. Heads and tails are assembled in separate pathways. With respect to other tailed phages, myoviruses tend to have larger heads and higher particle weights and DNA contents, and seem to be more sensitive to freezing and thawing and to osmotic shock. Genera are differentiated by genome organization, mechanisms of DNA packaging and presence or absence of unusual bases and DNA polymerases.