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Type Species |
(MBV) |
Virions are bacilliform, non-enveloped and lack prominent surface projections. Typically, virions are 19 
50 nm, but range between 18-20 nm in width and 48-53 nm in length (Fig. 1). Optical diffraction patterns of the virions resemble those of Alfalfa mosaic virus, suggesting a morphological subunit diameter of about 10 nm and a T = 1 icosahedral symmetry.
Physicochemical and Physical Properties
Virion Mr is 7.1 106, buoyant density in Cs2SO4 is 1.32 g/cm3. Virions are stable between pH 6 and 8 and isotonic strength of 0.01 to 0.1 M phosphate, and are insensitive to chloroform.
Virions contain a single linear molecule of a positive sense ssRNA, 4.0 kb in size. The complete 4009 nts sequence is available. The RNA appears to be uncapped and lacking a poly(A) tail. RNA constitutes about 20% of virion weight.
Virions contain a single major capsid protein (CP) (Mr 24.4 103). There are probably 240 molecules forming the capsid.
None reported.
None reported.
Genome Organization and Replication
The RNA genome (4009 nts) contains four major and three minor ORFs and has 5
and 3 non-coding regions of 60 nts and 250 nts, respectively. ORFs 1 to 4 encode polypeptides of Mr 20, 73, 47, and 22 103, respectively. ORF3 encodes a putative RNA-dependent RNA polymerase and ORF4 encodes the CP. The deduced amino acid sequences of both ORFs 2 and 3 contain putative helicase-like motifs. ORFs 5 to 7 encode polypeptides of Mr 8, 6.5, and 6 103, respectively. The polypeptides potentially encoded by ORFs 1, 5, 6 and 7 show no homology to known polypeptides (Fig. 2).
In a cell-free system, the RNA directs the synthesis of a major polypeptide (Mr 77 103), and possibly several minor polypeptides (Mr 21-37 103). The full-length genomic RNA and a putative subgenomic RNA (1.8 kb) are found in infected cells. Virions accumulate singly or as aggregates in the cytoplasm.
Mushroom bacilliform virus is highly immunogenic.
The virus infects the common cultivated botton mushroom (Agaricus bisporus). Bacilliform particles, which are morphologically similar to MBV, have been observed in the field mushroom A. campestris. Transmission is horizontal via mycelium and possibly basidiospores. Distribution of MBV coincides with that of the commercial cultivation of A. bisporus; the virus has been reported to occur in most major mushroom-growing countries. MBV is capable of autonomous replication, but commonly occurs as a double infection with a dsRNA virus (La France isometric virus, LIV) in mushrooms afflicted with La France disease. MBV is not required in pathogenesis involving LIV, but it remains to be determined if it is a second, minor causal agent of La France disease, the etiologic agent of an unrecognized pathology or benign. MBV RNA and LIV dsRNA do not share extensive sequence homology.
List of Species Demarcation Criteria in the Genus
Not applicable.
Official virus species names are in italics. Tentative virus species names, alternative names ( ), strains or serotypes are not italicized. Virus names, genome sequence accession number [ ], and assigned abbreviations ( ) are:
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Mushroom bacilliform virus |
[U07551] |
(MBV) |
Tentative Species in the Genus
None reported.
Phylogenetic Relationships within the Family
None reported.
Amino acid sequence of the putative RNA-dependent RNA polymerase and CP suggests an evolutionary relationship with plant viruses, particularly luteoviruses and carmoviruses.
Barna: sigla from bacilliform-shaped RNA viruses.
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