Abstract
The entomopathogenic fungus Beauveria bassiana has a wide host range and is used as a biocontrol agent against arthropod pests. Mycoviruses have been described in phytopathogenic fungi while in entomopathogenic fungi their presence has been reported only rarely. Here we show that 21.3% of a collection of B. bassiana isolates sourced from worldwide locations, harbor dsRNA elements. Molecular characterization of these elements revealed the prevalence of mycoviruses belonging to the Partitiviridae and Totiviridae families, the smallest reported virus to date, belonging to the family Narnaviridae, and viruses unassigned to a family or genus. Of particular importance is the discovery of members of a newly proposed family Polymycoviridae in B. bassiana. Polymycoviruses, previously designated as tetramycoviruses, consist of four non-conventionally encapsidated capped dsRNAs. The presence of additional non-homologous genomic segments in B. bassiana polymycoviruses and other fungi illustrates the unprecedented dynamic nature of the viral genome. Finally, a comparison of virus-free and virus-infected isogenic lines derived from an exemplar B. bassiana isolate revealed a mild hypervirulent effect of mycoviruses on the growth of their host isolate and on its pathogenicity against the greater wax moth Galleria mellonella, highlighting for the first time the potential of mycoviruses as enhancers of biocontrol agents.
Highlights
Beauveria bassiana (Balsamo) Vuillemin is an entomopathogenic ascomycete belonging to the family Clavicipitaceae, order Hypocreales
In order to assess the presence of dsRNA elements in B. bassiana, we screened a well-characterized panel of isolates sourced from worldwide locations [11]
Eleven of the B. bassiana isolates harboring dsRNA elements were recovered directly from arthropods, while the rest were collected from soil and their preferred host is unknown (S1 Table)
Summary
Beauveria bassiana (Balsamo) Vuillemin is an entomopathogenic ascomycete belonging to the family Clavicipitaceae, order Hypocreales. It has a wide host range of approximately 750 arthropod species and a widespread geographical distribution. Mycoviruses have been described in a wide range of fungi and are classified into eleven major families, six accommodating single-stranded (ss) and five accommodating double-stranded (ds) RNA genomes. The former group includes the families Narnaviridae and Hypoviridae, while the latter includes the families Totiviridae and Partitiviridae. In B. bassiana the presence of dsRNA elements, virus-like particles and associated hypovirulence have been reported [7,8]; only two viruses belonging to the genus Victorivirus, family Totiviridae have been sequenced [9,10]
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