46Mycoviruses infect fungi, and while most persist asymptomatically, there are examples 47 of mycoviruses having both beneficial and detrimental effects on their host. Saccharomyces and Ustilago strains exhibit a killer phenotype conferring a growth advantage 49 over uninfected strains, whereas hypovirus-infected Cryphonectria parasitica displays defects in 50 growth, sporulation, and virulence. In this study we identify a dsRNA mycovirus in five 51Malassezia species. Sequence analysis reveals it to be a totivirus with two dsRNA segments: a 52 larger 4.5 kb segment with genes involved in viral replication and maintenance, and a smaller 53 1.4 kb segment encoding a novel protein. Furthermore, RNA-seq of virus-infected versus virus-54 cured Malassezia sympodialis revealed an upregulation of dozens of ribosomal components in 55 the cell, suggesting the virus subjects the cell to a large transcriptional burden. Given that 56Malassezia is the most abundant fungus on human skin, we assessed the impact of the 57 mycovirus in a murine cutaneous infection model and found infection with virus-infected strains 58 was associated with enhanced skin colonization and inflammatory response compared to virus-59 cured strains. Moreover, interferon-β expression was significantly upregulated in bone marrow-60 derived macrophages when challenged with virus-infected, compared to virus-cured M. 61 sympodialis, suggesting that the presence of the virus can induce an immunological response. 62 Although many recent studies have illuminated how widespread mycoviruses are, there are 63 relatively fewer in depth studies about their impact on disease caused by the host fungus. We 64 describe here a novel mycovirus in Malassezia and its possible implications in inflammatory 65 disorders of the skin and possibly other tissues. 66 Importance 67 Malassezia species represent the most common fungal inhabitant of the mammalian 68 skin microbiome, and are natural skin commensal flora. However, these fungi are also 69 associated with a variety of clinical skin disorders. Recent studies have reported associations of 70 Malassezia with Crohn's disease and pancreatic cancer, further implicating this fungal genus in 71 inflammatory and neoplastic disease states. Because M. sympodialis has lost genes involved in 72 RNAi, we hypothesized Malassezia could harbor dsRNA mycoviruses. Indeed, we report here a 73 novel mycovirus of the totivirus family in several Malassezia species, and characterized the 74 MsMV1 mycovirus of M. sympodialis. We found conditions that lead to curing of the virus, and 75 analyzed isogenic virus-infected/virus-cured strains to determine MsMV1 genetic and 76 pathogenic impacts. MsMV1 induces a strong overexpression of transcription factors and 77 ribosomal genes, while downregulating cellular metabolism. Moreover, MsMV1 leads to 78 increased pathogenicity in a murine model, and induced a significantly higher level of interferon-79 β expression in cultured macrophages. This study sheds light on the mechanisms of 80 pathogenicity of Ma...
