Since only one genus is currently recognized, the family description corresponds to the genus description.
Type species Acholeplasma phage L2
Virions are quasi-spherical, slightly pleomorphic, enveloped and about 80 nm (range 50–125 nm) in diameter (Figure 1). Size varies due to virion heterogeneity: at least three distinct virion forms are produced during infection. Thin-sections show virions with densely stained centers, presumably containing condensed DNA, and particles with lucent centers. The absence of a regular capsid structure suggests the Acholeplasma phage L2 (L2) virion is an asymmetric nucleoprotein condensation bounded by a lipid-protein membrane.
Virions are extremely heat-sensitive, relatively cold-stable and inactivated by nonionic detergents (Brij-58, Triton X-100 and Nonidet P-40), ether and chloroform. Viral infectivity is resistant to DNAse I and phospholipase A, but sensitive to pronase and trypsin treatment. UV-irradiated virions can be reactivated in host cells by excision and SOS DNA repair systems. Virions are relatively resistant to photodynamic inactivation.
Virions contain one molecule of infectious, circular, superhelical dsDNA. The phage L2 genome is 11,965 bp, with a G+C value of 32%. All ORFs are encoded in one strand. Several genes are translated from overlapping reading frames.
Virions contain at least four major proteins of about 64, 61, 58 and 19 kDa. Several minor protein bands are also observed in virion preparations. DNA sequence analysis indicates 15 ORFs (Table 1).
Table 1 Acholeplasma phage L2 ORFs
ORF size (codons)
putative integrase, gene is upstream from attP site
basic protein, putative major virion DNA-binding protein
putative integral membrane protein, has 27 amino acid N-terminal peptidase cleavage signal sequence
translation start site is 295 codons downstream from ORF13 start site and in same reading frame
has 26 aa N-terminal peptidase cleavage signal sequence
Virions and host cell membranes have similar fatty acid compositions. Variation of host cell membrane fatty acid composition leads to virions with corresponding fatty acid composition variations. Data indicate viral membrane lipids are in a bilayer structure.
L2 infection involves a noncytocidal productive infectious cycle followed by a lysogenic cycle in each infected cell. At least 11 overlapping mRNAs are transcribed from the DNA coding strand, from at least eight promoters. In non-cytocidal infection, progeny phages are released by budding from the host cell membrane, with the host surviving as a lysogen. Lysogeny involves integration of the phage L2 genome into a unique site in the host cell chromosome. The putative phage L2 attP integration site is CATCTTCAT–7nt-CTGAAGATA. Lysogens are resistant to superinfection by homologous virus but not by heterologous virus (apparently due to a repressor), and are inducible by UV-irradiation and mitomycin C.
Map of genome organization of Acholeplasma phage L2 (L2) showing ORFs as determined from analysis of the 11,965 bp sequence. The base on the 3’-side of the single BstE II cleavage site is taken as the first base of the DNA sequence. The map also shows locations of the phage L2 integration site (attP) and the two phage L2 DNA replication origin sites (ori1 and ori2).
(From Maniloff et al. (1994); with permission.)
Host range: the phage L2 infects Acholeplasma laidlawii strains. Other putative plasmaviruses have been reported to infect A. laidlawii (Acholeplasma phages v1, v2, v4, v5 and v7), A. modicum (Acholeplasma phage M1) and A. oculi strains (Acholeplasma phage O1).
Acholeplasma phage L2
Acholeplasma phage L2
Species names are in italic script; names of isolates are in roman script. Sequence accession numbers [ ] and assigned abbreviations ( ) are also listed.
Acholeplasma phage M1
Acholeplasma phage O1
Acholeplasma phage v1
Acholeplasma phage v2
Acholeplasma phage v4
Acholeplasma phage v5
Acholeplasma phage v7
No information available.
Plasma: from the Greek plasma, “shaped product”, referring to the plastic virion shape.
Dybvig, K. and Maniloff, J. (1983). Integration and lysogeny by an enveloped mycoplasma virus. J. Gen. Virol., 64, 1781-1785.
Maniloff, J. (1992). Mycoplasma viruses. In: J. Maniloff, R.N. McElhaney, L.R. Finch and J.B. Baseman (Eds.), Mycoplasmas: Molecular Biology and Pathogenesis. American Society for Microbiology, Washington, DC, pp. 41-59.
Maniloff, J., Cadden, S.P. and Putzrath, R.M. (1981). Maturation of an enveloped budding phage: mycoplasma virus L2. In: M.S. DuBow (Ed.), Bacteriophage Assembly, AR Liss Inc., New York, pp. 503-513.
Maniloff, J., Kampo, G.K. and Dascher, C.C. (1994). Sequence analysis of a unique temperate phage: mycoplasma virus L2. Gene, 141, 1-8.
Poddar, S.K., Cadden, S.P., Das, J. and Maniloff, J. (1985). Heterogeneous progeny viruses are produced by a budding enveloped phage. Intervirology, 23, 208-221.