Abstract
A clinical isolate of Aspergillus thermomutatus (Teleomorph: Neosartorya pseudofischeri) was found to contain ~35 nm isometric virus-like particles associated with four double-stranded (ds) RNA segments, each of which coded for a single open reading frame. The longest dsRNA element (3589 nt) encodes a putative RNA-dependent RNA polymerase (1114 aa), the second longest dsRNA element (2772 nt) encodes a coat protein (825 aa), and the other two dsRNAs (2676 nt, 2514 nt) encode hypothetical proteins of 768 aa and 711 aa, respectively. Phylogenetic analysis of the amino acid sequences showed 41–60% similarity to the proteins coded by the dsRNAs of the most closely related virus, Penicillium janczewskii chrysovirus 2, indicating that it is a new species based on the International Committee on Taxonomy of Viruses criteria for the genus Chrysovirus. This is the first virus reported from A. thermomutatus and was tentatively named Aspergillus thermomutatus chrysovirus 1. A virus free line of the fungal isolate, cured by cycloheximide treatment, produced large numbers of conidia but no ascospores at both 20°C and 37°C, whereas the virus infected line produced ten-fold fewer conidia at 20°C and a large number of ascospores at both temperatures. The effects of the virus on fungal sporulation have interesting implications for the spread of the fungus and possible use of the virus as a biological control agent.
Highlights
The vast majority of the reported mycoviruses contain double-stranded RNA genomes; a lesser number have single-stranded RNA genomes, while only a few mycoviruses possess single-stranded DNA [1]
DsRNAs are often the template of choice when investigating RNA viruses, as they represent either the genome or replicative form of most mycoviruses and are more stable and easier to purify than single-stranded RNA [2]
While the fungal cultures studied were originally derived from clinical isolates their origin was anonymous and the material analysed consisted of pure fungal cultures that contained no human material
Summary
The vast majority of the reported mycoviruses contain double-stranded (ds) RNA genomes; a lesser number have single-stranded (ss) RNA genomes, while only a few mycoviruses possess single-stranded DNA [1]. DsRNAs are often the template of choice when investigating RNA viruses, as they represent either the genome or replicative form of most mycoviruses and are more stable and easier to purify than single-stranded (ss) RNA [2]. Many Aspergillus species have been reported to be infected with mycoviruses, or uncharacterised dsRNA segments [3]. These include Aspergillus section Nigri [4, 5, 6], Aspergillus section Flavi [7], Aspergillus section Circundati, and section Fumigati [8], Aspergillus section Clavati [9], A. foetidus [10, 11], A. niger [12], A. flavus [13, 14, 15], A. fumigates [16, 17, 18, 19, 20] and A. ochraceus [21, 22], with an incidence of 7–50% in all examined species [3].
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