# Fungal Pigments and Their Roles Associated with Human Health
## 2 Types of Fungal Pigments and Their Relevance to Human Health
### Carotenoids  
In addition to being produced by photosynthetic organisms ranging from cyanobacteria to flowering plants, carotenoids are also synthesized in a variety of heterotrophic microbes including fungi [13]. Furthermore, carotenoids are present in animals that are unable to synthesize them de novo, but instead acquire them from their diet. Carotenoids contain an aliphatic polyene chain usually composed of eight isoprene units that include light-absorbing conjugated double bonds, giving rise to characteristic colors such as yellow, orange, or red [14; 15]. Representative structures of carotenoids are shown in Figure 1. Some carotenoids are precursors of vitamin A, specifically those with \(\beta\)-ring end groups, such as \(\beta\)-carotene, zeaxanthin, and \(\beta\)-cryotoxanthin [8]. From the standpoint of human health, carotenoids are among the bioactive products with significant medical value. For example, carotenoids have been found to lower the risks of diseases, including cancer, cardiovascular diseases, and age-related eye disorders, such as macular degeneration and cataracts [16]. Figure 1: Structure of representative carotenoids. Carotenoid-producing fungi are very diverse, including _Rhodotorula mucilaginousa_[17], _Blakesela trispora, Phycomyces blackseleamus, Mucor circinelloides, Fusarium sporotrichoides_[18], _Rhodosporium pulidigenum_, and _Rhodotorula glutinis_[19]. Carotenoids protect fungi from oxidative stress and non-ionizing irradiation such as UV light. In addition, carotenoids are intermediates essential for synthesizing other biological molecules including bioactive apocarotonoids and related constituents. For instance, in many filamentous fungi, retinol, the precursor of vitamin A as well as an essential component of rhodopsins (membrane-bound photoreceptors), is produced via the oxidative cleavage of \(\beta\)-carotene [20]. In Mucorales, \(\beta\)-carotene is an intermediate during the synthesis of trisporoids, apocarotonoid derivatives that include the sexual hormones the trisporic acids. In addition, trisporoids have been proposed as substrates in the synthesis of sporopolenin, one of the most chemically inert biological polymers primarily found in the tough outer walls of plant spores and pollen grains [15]. In some fungi, such as the filamentous species _Blakesela trispora_[21] and the yeast _Rhodotorula_ spp. [22], the \(\beta\)-carotene biosynthetic pathway also produces lycopene, a carotenoid intermediate. Lycopene is a nutrient with antioxidant properties. It was originally identified in plants such as tomato and watermelon, giving their fruits the characteristic red and pink colours. Lycopene has been linked to several human health benefits ranging from improved cardiovascular health to protection against sunburns and certain types of cancers. Aside from \(\beta\)-carotene and lycopene, another fungal carotenoid, astaxanthin, has attracted significant attention for its promise in the pharmaceutical, food and cosmetics industries. For example, astaxanthin has shown promise for treating Alzheimer's disease, Parkinson's disease, stroke, high cholesterol, age-related macular degeneration (age-related vision loss), and preventing cancer. _Xanthophyllomyces dendrorhous_ (synonym _Phaffia rhodozyma_), a red- or orange-pigmented basidiomycetous yeast initially isolated from Japanese and Alaskan tree-exudates decades ago, is capable of producing astaxanthin [23; 24]. Astaxanthin is synthesized via the mexolonate pathway starting with a condensation of two molecules of geranylgeranyl pyrophosphate, a four-step desaturation, cyclization, and a final 4-ketolation plus 3-hydroxylation [25; 26]. In addition to astaxanthin, _X. dendrorhous_ can also utilize the mexolonate pathway to produce several other types of carotenoids including \(\beta\)-carotene, canthaxanthin, and zeaxanthin. Canthaxanthin is used to reduce sensitivity to sunlight (photosensitivity) experienced by people who have a rare genetic disease called erythropoietin (EPP) [27].