Genus “P1-like Viruses”

Type Species	Enterobacteria phage P1	(P1)

Distinguishing Features

Virions are large, produce head size variants, and aggregate pairwise by tail cores. DNA is circularly permuted and terminally redundant, and is packaged from a pac site by a headful mechanism. The genetic map is linear. Prophages generally persist as plasmids.

Virion Properties

Morphology

Virions have icosahedral heads of about 85  nm in diameter and produce head size variants (about 65 and 47  nm). Tails measure 228 18  nm in Enterobacteria phage P1 (P1) and vary in length between 170 and 240  nm in other representatives (Enterobacteria phage P1D (P1D), Aeromonas phage 43 (43)). Tails have base plates and six 90  nm-long kinked fibers. Particles with contracted tails aggregate side-by-side by means of exposed tail cores.

Physicochemical and Physical Properties

Virion buoyant density is 1.48  g/cm³.

Nucleic Acid

Genomes are about 100  kbp in size and have a G+C content of 46%.

Proteins

Virions contain 24-28 constitutive proteins (Mr 10-220 10³), including a major CP (Mr 44 10³).

Lipids

Not known.

Carbohydrates

Not known.

Genome Organization and Replication

The genetic map is linear and includes about 100 genes; related functions are often distributed over several genome regions. The prophage map is circular. The genome is circularly permuted and terminally redundant (8-12%), and includes a recombinational hot spot (lox-cre). The genome has also an invertible segment of about 4  kbp (C-loop) that is homologous to the G-loop of Enterobacteria phage Mu (Mu). Virion DNA circularizes after injection. Replication starts at a single site and comprises a phase of rings and a later phase of structures, suggesting a rolling-circle mechanism. Progeny DNA is cut from concatemers at a pac site and packaged by a headful mechanism.

Antigenic Properties

Enterobacteria phages P1, P2, and Mu share tail fiber antigens.

Biological Properties

Phages are temperate and general transductants, and infect enterics and related Gram-negative bacteria. Prophages are maintained as plasmids (1-2 per cell) or integrate (rarely) at specific sites into the bacterial chromosome. Prophages are weakly UV-inducible. The invertible C-loop codes for two sets of tail fibers and provides a means of extending host range.

List of Species Demarcation Criteria in the Genus

Species differ in host range and tail length (P1, 228  nm; P1D, 240  nm; 43, 170  nm).

List of Species in the Genus

Official virus species names are in italics. Tentative species names, alternative names ( ), strains or serotypes are not italicized. Virus names and assigned abbreviations ( ) are:

Species in the Genus

Aeromonas phage 43	(43)
Enterobacteria phage P1	(P1)
Enterobacteria phage P1D	(P1D)
Enterobacteria phage P7	(P7)

Tentative Species in the Genus

Acetobacter phage pKG-2	(pKG-2)
Acetobacter phage pKG-3	(pKG-3)
Enterobacteria phage D6	(D6)
Enterobacteria phage W39	(W39)
Enterobacteria phage j2	(j2)
Pseudomonas phage PP8	(PP8)
Vibrio phage VP253	(VP253)
Vibrio phage P147	(P147)