Can mycoviruses be used as biological control agents against Aspergillus?

Abstract

Mycoviruses are becoming increasingly recognised for their potential as biocontrol agents against phytopathogenic fungi which has raised the question to what extent mycoviruses could be effective and applicable to the control of Aspergillus, possibly including human infections. A total of 50 clinical and environmental Aspergillus isolates were screened for the presence of dsRNAs, indicative of mycovirus infection. Eight isolates contained dsRNAs, six of which also contained isometric virus-like particles. Of particular interest was an isolate of Aspergillus thermomutatus which exhibited very low asexual sporulation. Sequencing of the dsRNAs identified the virus as a chrysovirus, tentatively named Aspergillus thermomutatus chrysovirus 1 (AthCV1), the genome of which consists of four segments encoding; a putative RNA-dependent RNA polymerase (3589 nt, 1114 aa), a CP (2772 nt, 825 aa), and two HPs (2676 nt, 768 aa and 2514 nt, 711 aa). A genetically identical virus free A. thermomutatus line, cured by cycloheximide treatment, produced large numbers of conidia but no ascospores at both 20⁰C and 37⁰C, whereas the virus infected line produced large numbers of ascospores at both temperatures and ten-fold fewer conidia at 20⁰C. To study possible effects of AthCV1 on other Aspergillus species, virus free isolates of A. fumigatus, A. nidulans and A. niger were transfected with AthCV1 particles and their phenotypic reaction assessed. Both virus free and virus infected A. fumigatus produced only conidia at both temperatures, but with at least a ten-fold reduction in sporulation in the virus infected line. Conidial production was also significantly reduced in the infected lines of A. nidulans and A. niger at 37⁰C. Transcriptome profiling of virus free and virus infected isolates of all four Aspergillus species at 37⁰C showed changes in the expression of a variety of genes with a wide range of functions, including several genes with known roles in sexual and/or asexual sporulation. The successful virus transfection to different Aspergillus species accompanied by the substantial decrease in A. fumigatus sporulation at both 37⁰C and 20⁰C provides a starting point for evaluating the potential of mycoviruses as an alternative control method to treat Aspergillus infection.