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Double-stranded RNA viruses in a mycocinogenic strain of Cystofilobasidium infirmominiatum

Wladyslav I Golubev1, Ilona Pfeiffer, Ludmila G Churkina

  • 1Russian Collection of Microorganisms (VKM), Institute for Biochemistry and Physiology of Microorganisms, Russian Academy of Sciences, 142290, Pushchino, Russia. wig@ibpm.serpukhov.su

FEMS Yeast Research
|April 19, 2003
PubMed

Insights

Researchers discovered viral particles containing double-stranded RNAs (dsRNAs) in a fungicidal fungus, Cystofilobasidium infirmominiatum. Removing these dsRNAs eliminated the fungus

Area of Science:

  • Mycology
  • Virology
  • Biochemistry

Background:

  • Fungal viruses, particularly those encoding mycotoxins, are of significant interest.
  • Cystofilobasidium infirmominiatum is known to secrete a fungicidal compound (mycocin).
  • The genetic basis of mycocin production and its relationship with potential viral infections in this fungus remain largely unexplored.

Purpose of the Study:

  • To investigate the presence and nature of viral particles in a mycocin-secreting strain of Cystofilobasidium infirmominiatum.
  • To determine the relationship between the detected viral components and the mycocinogenic activity of the fungus.
  • To characterize the mycocin and its target organisms.

Main Methods:

  • Isolation and characterization of viral particles from Cystofilobasidium infirmominiatum.
  • Analysis of double-stranded RNA (dsRNA) content within the viral particles.
  • Fungal 'curing' experiments involving incubation at elevated temperatures.
  • Assays to determine mycocin activity, molecular mass, optimal pH, and spectrum of activity.
  • Sensitivity testing of cured fungal strains against the parent strain's mycocin.

Main Results:

  • Viral particles (approximately 30 nm in diameter) containing dsRNAs (2.0 and 6.3 kbp) were identified within the mycocin-secreting strain.
  • The mycocin, with a molecular mass >15 kDa, exhibits fungicidal activity, primarily against species in the Cystofilobasidiales and Filobasidiales orders (e.g., 'Cryptococcus aerius' clade), with optimal activity at pH 4.5.
  • Heat treatment ('curing') led to the loss of both dsRNAs and mycocin production, rendering the cured strains susceptible to the mycocin from the original strain.

Conclusions:

  • The study provides strong evidence for the involvement of viral dsRNAs in the mycocinogenic activity of Cystofilobasidium infirmominiatum.
  • The mycocin produced by this fungus is a potent fungicidal agent effective against specific fungal groups.
  • Viral infection and the presence of dsRNAs appear essential for mycocin production in this strain, suggesting a virus-encoded or virus-mediated mechanism.

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