Malassezia yeast exist on all humans and have long been associated with healthy and diseased skin. In this Article Collection of Frontiers in Cellular and Infection Microbiology; Fungal Pathogenesis, we will present multiple papers outlining the state of the art in understanding the role Malassezia in skin health and disease.
Over the last thirty years, the term “microbiome” has grown exponentially in scientific discourse, generating hundreds of thousands of publications and patents. Although the human-associated microbial community consists of bacteria, fungi, viruses, and archaea, the vast majority of these publications have been limited to gut bacteria. Only in the two decades has the “mycobiome”, or fungal community, begun to appear as a research topic, with fewer than 3,500 research publications listed in google scholar. To date, human mycobiome research has focused on skin, as fungi constitute a larger percentage of skin than gut microbiomes, representing 5-10% of skin metagenomic sequences versus less than 1% in the gut. Also, the skin mycobiome is less complex and dominated by members of a single genus, Malassezia, and skin is much less complex to sample.
Originally thought a single species, Malassezia is now known to span an entire clade consisting of 18 diverse species, found on all humans and all warm-blooded animals, and ecosystems as diverse as deep marine environments. As Malassezia spp. inhabit the interface of “self” with the external world they are impacted both from inside and out, with host and co-inhabitant microbes, environment, lifestyle choices (i.e. diet and product usage, hygiene), and immune activity affecting their biology and hence pathogenesis. Importantly, beyond their commensal lifestyle on the host skin, Malassezia spp. are also associated with various pathological conditions, including dandruff, pityriasis versicolor and common inflammatory skin disorders such as seborrheic dermatitis (SD) and atopic dermatitis (AD). While in some cases, disease is linked to the appearance of Malassezia hyphae and fungal overgrowth, the causal relationship between the fungus and disease in case of SD or AD remains less clear. Malassezia also inhabits another human/environment interface, the gut. While less well defined than in skin, important interactions between gut Malassezia and the immune system have been shown to be involved in Crohn’s disease and maybe a larger component of human gut health than previously understood.
Host susceptibility is also critical, making it necessary for mechanistic studies of fungal pathogenesis to be carried out longitudinally in susceptible hosts. It remains controversial whether Malassezia spp. are commensal or pathogenic, and likely can be either in specific circumstances. In this collection we will include papers describing the current state of the art in Malassezia research including: species diversity (human, animal, and other); skin (and gut) microbiome; niche- and species-specific adaptation; comparative genomics, sex, and hybridization; metabolomics (including lipids and small molecules); virulence factors; microbe/host interactions and immunology; clinical and veterinary implications, and therapy and resistance. Together, these papers should contribute to a step change in our ability to assess the functional role of Malassezia in skin health and disease.
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Journal of Clinical & Experimental Dermatology Research