S1.3c Diversity and hybridization in Malassezia furfur

Abstract S1.3 Malassezia: genetics, genomics, and biology, September 21, 2022, 11:00 AM - 12:30 PM   The Basidiomycetous yeast Malassezia is the most abundant fungal genus on healthy human skin but may also cause various skin disorders such as seborrheic dermatitis, dandruff, and pityriasis versicolor. In recent years, Malassezia has increasingly been implicated in health and disease beyond the skin: as an underestimated cause of Malassezia bloodstream infections (BSIs) in immunocompromised patients and neonates, associated with Crohn's disease, promoting pancreatic oncogenesis, and exacerbating cystic fibrosis. Malassezia furfur is the number one Malassezia BSI cause and is also implicated in many skin disorders. With these new discoveries of Malassezia’s impact on human health, the need for a better understanding of its evolution and pathobiology also became more pressing. Hybridization has been suggested as a biological mechanism of adaptation to new hosts, and may lead to increased pathogenicity. Many examples of major hybrid yeast pathogens exist, such as Candida albicans, C. orthopsilosis, C. metapsilosis, and multiple examples in the Cryptococcus gattii/Cryptococcus neoformans species complex. Here the multiple hybridization events of the Malassezia furfur species complex will be discussed. Two distinct hybridization events occurred between the same parental lineages, and these parental strains were originally also hybrids. The identification of a pseudobipolar mating system and the analysis of the mating-type loci provide evidence that sexual liaisons of mating compatible cells from these parental lineages led to a diploid/aneuploid state in the hybrid lineages. Sequence similarity percentages suggest that both parental lineages in fact are two different species. The genetic diversity of ca 300 strains belonging to this species complex is evaluated in relationship to host background and phenotype.