Malassezia is the most prevalent fungus identified in the human skin microbiota; originally described at the end of the nineteenth century, this genus is composed of at least 14 species. The role of Malassezia on the skin remains controversial because this genus has been associated with both healthy skin and pathologies (dermatitis, eczema, etc.). However, with the recent development of next-generation sequencing methods, allowing the description of the fungal diversity of various microbiota, Malassezia has also been identified as a resident fungus of diverse niches such as the gut or breast milk. A potential role for Malassezia in gut inflammation and cancer has also been suggested by recent studies. The aim of this review is to describe the findings on Malassezia in these unusual niches, to investigate what is known of the adaptation of Malassezia to the gut environment and to speculate on the role of this yeast in the host physiology specifically related to the gastrointestinal tract.
Two reports were published in 2019 on the role of Card9 in the regulation of the fungal burden, myeloidderived suppressor cell expansion and inammasome activation, allowing the restriction of CRC or CAC development (Malik et al., 2018; Wang et al., 2018). CARD9 indeed participates in the recognition of microorganisms, especially fungi, through several receptors, such as Mincle, NOD2, and Dectin, and thus orchestrates an important part of the host response against fungi from simple overgrowth to deep infection (Richard et al., 2015). Additionally, in 2019, chitooligosaccharides were shown to prevent the development of CAC through their eect on the balance between bacterial and fungal microbiota (Wu et al., 2019). In addition to these results, several other publications, which are presented in the next chapter, descr
id: 47c0c28ecd22aae7ec9a7cb6305a4670 - page: 6
Finally, recently, MALASSEZIA INFLUENCES GUT HEALTH As highlighted earlier in this review, although a well-described resident of the skin, Malassezia, appears to be a prominent component of the gut mycobiota, numerous studies have identied Malassezia in fecal samples through culture-dependent Frontiers in Cellular and Infection Microbiology | www.frontiersin.org 6 Malassezia in Gut Health
id: 8dad8707d9ddfd8b9f8fb9e025a7969f - page: 6
, 2011; Hamad et al., 2012; Gouba et al., 2013; Suhr et al., 2016; HallenAdams and Suhr, 2017). Malassezia has been reported in healthy volunteers as a major genus, reaching up to 4% of the total abundance (Gouba et al., 2013; Suhr et al., 2016; Raimondi et al., 2019). M. restricta (Hamad et al., 2012; Gouba et al., 2013; Suhr et al., 2016; Nash et al., 2017; Auchtung et al., 2018), M. globosa (Hamad et al., 2012; Gouba et al., 2013; Nash et al., 2017), M. pachydermatis (Chen et al., 2011; Hamad et al., 2012; Gouba et al., 2013), and M. sympodialis (Nash et al., 2017) are the main species that can be found in the gastrointestinal tract. However, these previous studies made very few cases of this presence, mostly considering it transient and with no eect on the host. It is only very recently that Malassezia strains have been specically identied in association with gut diseases and possibly other types of diseases (Figure 1).
id: ebb26f11b82e5c3368bec0e695410a39 - page: 6
The Impact of Malassezia on IBD The Malassezia genus has only very recently been associated with IBD, both in patients and in mouse models. IBD is composed of two types of disease: Crohns disease (CD) and ulcerative colitis (UC). Both are characterized by inammation of the wall of the digestive tract, from the mouth to the rectum for CD and only for the colon for UC (Seyedian et al., 2019). Two studies highlighted the potential role of Malassezia in the development of IBD in the last 3 years: (i) our study while characterizing the global modications of the bacterial and fungal microbiota for UC and CD patients (Sokol et al., 2017); (ii) and Limon and coworkers in a specic study focused on CD patients (Limon et al., 2019).
id: d366b10a4856936afb157702b6892a90 - page: 6