From Dandruff to Deep-Sea Vents: Malassezia-like Fungi Are Ecologically Hyper-diverse

As the dominant component of the mycobiota on human skin 1 —both healthy and diseased 2 —the genus Malassezia has received a fair amount of attention. Since the middle of the 19th century, researchers have linked these fungi with skin maladies such as dandruff and eczema 3, but their difficulty to culture axenically long hampered studies of their systematics and diversity 4. Malassezia is the sole genus within the fungal order Malasseziales, contained within the proposed subphylum Malasseziomycetes (anonymous reviewer; personal communication). Although Malassezia is sister to the so-called “smut” plant pathogens, they are markedly divergent in ecological terms. A hallmark of Malassezia species is their incomplete fatty acids synthesis metabolic pathway, and reliance, instead, on a suite of extracellular lipases, phospholipases, and acid sphingomyelinases 5. In fact, only a single species, M. pachydermatis, is able to survive in axenic culture lacking lipid amendment 6. Until recently, it was assumed that Malassezia evolved into a specialized and narrow niche associated with the skin of mammalian hosts. However, culture-independent studies of fungi from environmental samples show that Malassezia are exceedingly widespread and ecologically diverse 3. Recent studies in little-characterized marine environments point to extensive diversification of Malassezia-like organisms, providing exciting opportunities to explore the ecology, evolution and diversity of this enigmatic group.