A mycovirus shaped insect-pathogenic and non-pathogenic phenotypes in a fungal biocontrol agent

Summary

Scientists discovered that a virus living inside a beneficial fungus is responsible for the fungus’s ability to kill insect pests. When they removed the virus, the fungus completely lost its ability to penetrate and infect insects through their skin, but could still cause infection if injected directly into the insect’s body. This finding suggests that the virus controls a key enzyme needed for the fungus to break through the insect’s protective outer layer, opening new possibilities for creating more effective biological pest control agents.

Background

Entomopathogenic ascomycetes (EA) like Beauveria bassiana are used as biological control agents against insect pests, but their effectiveness is limited by slow action and poor environmental persistence. Mycoviruses are increasingly recognized for their potential to modulate fungal virulence and enhance biocontrol efficacy.

Objective

This study investigated the role of Beauveria bassiana victorivirus 1 (BbVV-1) as a virulence determinant in B. bassiana strain EABb 01/33-Su by comparing mycovirus-infected and mycovirus-free strains to elucidate the mechanisms underlying mycovirus-mediated pathogenicity.

Results

The mycovirus-infected WMI strain demonstrated broad-spectrum virulence across insect orders, while the mycovirus-free MFr strain was completely non-pathogenic via contact. The MFr strain exhibited complete suppression of extracellular Pr1 protease and other cuticle-degrading enzymes, though virulence was restored through direct hemocoel injection. WMI showed time-dependent increases in pr1 gene copies and fungal DNA during infection, while neither were detected in MFr.

Conclusion

This research provides the first evidence of a mycovirus functioning as an essential virulence factor in an entomopathogenic fungus, with BbVV-1 acting as a critical determinant of cuticle penetration capability through regulation of Pr1 protease expression, offering potential applications in enhancing biocontrol efficacy or engineering safer fungal biocontrol agents.
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