Genus “P2-like viruses”

Type Species	Enterobacteria phage P2	(P2)

Distinguishing Features

Mature DNA is nonconcatemeric and packaged in circular form. Virion DNA has cos sites.

Virion Properties

Morphology

Phage heads are icosahedral, measure about 60  nm in diameter, and consist of 72 capsomers (60 hexamers and 12 pentamers; T = 7). Tails measure 135 18  nm and have a collar and 6 short kinked fibers.

Physicochemical and Physical Properties

Virion Mr is 58 10⁶; buoyant density in CsC1 is 1.43  g/cm³; S_20w is 283S.

Nucleic Acid

Genomes are about 34  kbp in size, correspond to about 48% of particle weight, and have a G+C content of 52%. The genome of the related Haemophilus phage HP1 (HP1) has been fully sequenced.

Proteins

Virions contain at least 13 structural proteins (Mr 20-94 10³), including 484 (420?) copies of the major CP (Mr 39 10³). Amino acid sequences for HP1 are available at GenBank and EMBL.

Lipids

Not known.

Carbohydrates

Not known.

Genome Organization and Replication

The genetic map is linear and nonpermuted, has cos sites, and includes about 40 genes. Transcription starts in the right half of the genome, has two phases (early, late), and depends on host RNA polymerases. Replication starts at a single site, is unidirectional, and follows a modified rolling-circle mechanism. DNA is cut from concatemers at specific sites and packaged into proheads as a covalently closed circle.

Antigenic Properties

Enterobacteria phage P2 (P2), Enterobacteria phage P1 (P1), and Enterobacteria phage Mu (Mu), share tail fiber antigens.

Biological Properties

Phages are temperate, adsorb to the cell wall, and infect enterics and related Gram-negative bacteria. Prophages may integrate at some 10 specific sites of the bacterial chromosome and are not UV-inducible. P2 acts as a “helper” for defective Enterobacteria phage P4 (P4) in providing head and tail genes for P4 propagation.

List of Species Demarcation Criteria in the Genus

Species differ in host range and DNA homology.

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, genome sequence accession numbers [ ], and assigned abbreviations ( ) are:

Species in the Genus

Enterobacteria phage P2		(P2)
Haemophilus phage HP1	[U24159]	(HP1)
Haemophilus phage S2		(S2)

Tentative Species in the Genus

Aeromonas phage 29	(29)
Aeromonas phage 37	(37)
Agrobacterium phage PIIBNV6	(PIIBNV6)
Caulobacter phage Cr24	(Cr24)
Enterobacteria phage 186	(186)
Enterobacteria phage 299	(299)
Enterobacteria phage Beccles	(Beccles)
Enterobacteria phage Pk2	(Pk)
Enterobacteria phage W	(W)
Pasteurella phage AU	(AU)
Pseudomonas phage CTX	(CTX)
Pseudomonas phage PsP3	(PsP3)
Rhizobium phage gal-1/R	(gal-1/R)
Rhizobium phage WT1	(WT1)
Vibrio phage X29	(X29)