Incidence and stability of infection by double-stranded RNA genetic elements inAspergillussectionflaviand effects on aflatoxigenicity

Abstract

Ninety-two isolates belonging to Aspergillus sect. j7avi were analyzed for double-stranded (ds) RNA via standard cellulose chromatography. Double-stranded RNA infection was detected in fungal isolates that had been in culture for long periods (5 of 26 were infected) and in those recently isolated (5 of 66 were infected). The number of dsRNA genetic elements differed among infected isolates and no two isolates contained identical dsRNAs on the basis of electrophoretic migration in agarose gels. Addition of micronutrients to culture media affected both the amount of dsRNA produced and the number of dsRNA genetic elements detected. Attempts to cure six fungal isolates of dsRNA by serial single conidial transfer, chlorate selection for nitrogen-metabolism mutants, and cycloheximide treatment, met with variable results. The frequency at which serial single conidial transfer and nitrogen-metabolism mutant (nit) selection successfully cured six Aspergillus sect. j7avi isolates varied from 11 to 100% and 0 to loo%, respectively. The cycloheximide treatment was effective at curing 40% of the dsRNA-infected isolates. Comparison of aflatoxin production prior to and after dsRNA curing indicated that infection by dsRNA did not influence aflatoxin production. However, aflatoxin production by two isolates (91-03 1B and 91-1846) was reduced by both single conidial transfer and induction of nit mutants.RCsumC : Les auteurs ont analysC 92 isolats de 1'Aspergillus sect. j7avi pour dttecter 1'ARN doubles brins, en utilisant la chromatographie de base sur cellulose. Une infection par ARN 6 doubles brins a Ct C dtcel6e chez des isolats fongiques prialablement cultivCs depuis longtemps (5 sur 26 portent une infection) et chez ceux cultivCs depuis peu (5 sur 66 portent une infection). Les nombres d'kltments ARN 2 doubles brins diffkrent entre les isolats infect& et, sur la base de la migration ClectrophorCtique sur gels d'agarose, aucun des isolats ne contient des ARNs 6 doubles brins identiques. L'addition de micronutriments aux milieux de culture affecte la quantite d'ARN a doubles brins aussi bien que le nombre d'ClCments gCnCtiques ARN 6 double brins dttectb. Les auteurs ont obtenu des resultats variables, aprks avoir tent6 d'Climiner I'ARN 6 doubles brins chez six isolats fongiques en conduisant une sCrie de transfert a partir de conidies individuelles, en effectuant une sClection de mutants pour le mCtabolisme azotC sur chlorate ou en les traitant 6 la cycloheximide. La frtquence a laquelle les transferts de conidies isolCes et la sClection de mutant du mCtabolisme azotC (nit) ont rkussi 6 gutrir six isolats de I'Aspergillus sect. j7avi va de 11 5 loo%, et de 0 6 loo%, respectivement. Le traitement a la cycloheximide 6 permis de gutrir 40% des isolats infect& par des ARN 6 doubles brins. Une comparaison de la production d'aflatoxine, avant et aprks llClimination des ARN 6 doubles brins, indique que l'infection par ces ARNs n'influence pas la production d'aflatoxine. Cependant, la production d'aflatoxine par deux isolats (91-031B e...

Time course of virus-like particles (VLPs) double-stranded rna accumulation in toxigenic and non-toxigenic strains of Aspergillus flavus

“…This agree with the findings of Elias and Cotti (8), who detected dsRNA in 10 out of 92 strains of Aspergillus seção Flavi and found no correlation between production of aflatoxins and presence dsRNA, as previously suggested (16,24). According to these authors, the molecular size estimates of the dsRNA components ranged from 0.4 to greater than 10.0 Kb, relative to the migration of dsRNA fragments of phage submitted to digestion with hindIII.…”

“…Several Aspergillus species have been found to be infected with mycoviruses, including A. foetidus (4,17), Aspergillus section Circundati and Fumigati (23), Aspergillus section Nigri and section Flavi (8,22).…”

“…Strain NRRL 5565 cured of dsRNA infection by exposing it to an RNA synthesis inhibitor (cicloheximide) developed the ability to produce aflatoxins (18); furthermore, after artificial infection with virus isolated from P. chrysogenum, the production of aflatoxins ceased. However, Elias and Cotti (8) detected dsRNA genomic elements in 10 out of 92 isolates of Aspergillus section Flavi yet the aflatoxin-producing ability of the isolates was not affected by dsRNA infection (16,24).…”

The effects of dsRNA mycoviruses on growth and murine virulence of Aspergillus fumigatus

“…Cycloheximide was first used to cure yeast of dsRNA virus infection (Fink and Styles, 1972) and subsequently used in a similar fashion to cure Aspergillus spp. of mycovirus infection (Elias and Cotty, 1996) and here with AfuCV. Only the highest concentration of cycloheximide of 150 mM investigated was successful in curing wild-type, A. fumigatus isolate A-56 of infection with AfuCV to produce isolate A-56-C but the treatment did cause a dramatic reduction in growth rate.…”

The Ecology and Evolution of Fungal Viruses

“…In some fungi, transmission through conidia can be close to 100%, making it difficult to obtain virus-free isogenic isolates (Coenen et al, 1997;Ikeda et al, 2004;Park et al, 2006;Polashock and Hillman, 1994;van Diepeningen et al, 2006). In other systems, transmission may be intermediate and variable in frequency (Brasier, 1983;Elias and Cotty, 1996). For example, Heterobasidion annosum virus (HaV, family Partitiviridae, genus Partitivirus) was transmitted to 3% of conidia in one isolate of the basidiomycete tree pathogen H. annosum and 55% in another (Ihrmark et al, 2002).…”