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 littlecharacterized marine environments point to extensive diversification of Malassezia-like organisms, providing exciting opportunities to explore the ecology, evolution and diversity of this enigmatic group.