# Production of Fungal Pigments: Molecular Processes and Their Applications
## 3 Stress Factors and Fungal Pigment Production
In addition, further investigation in the high-altitude lake ecosystem located in the Nahuel Huapi National Park (Bariloche, Argentina) revealed that living microorganisms have adopted such strategies as the synthesis of antioxidants and UV sunscreen compounds, including carotenoids and mycosporines, to minimize UV-induced damage [96]. Specifically, [PERSON] et al. reported that: (i) 24 yeast species were recovered, among which at least four represented novel species; and (ii) carotenogenic yeasts dominated in lakes with higher water transparency (more UV exposure). Taken together, the results suggest UV radiation as an important environmental factor eliciting yeast carotenoid pigment production and thereby affecting the microbial community structure in aquatic habitats. Similarly, oxidative stress has been found to induce increased hypocrellin production in _Shiraia bambusicola_, a well-known pathogenic fungus of bamboo. Hypocrellins, red pigments belonging to the class of perylenequinonoids, are considered as significant photosensitizers, which can serve as potential new-generation photodynamic therapy (PDT) drugs. Hypocrellins, during illumination, display excellent anticancer [97; 98; 99; 100] and antiviral activities [101]. Additionally, hypocrellin has been long used in Chinese folk medicine for the treatment of skin diseases and stomach aches. For example, a recent study by [PERSON] et al. [102] assessed the biomass and hypocrellin biosynthesis of _Shiraia_ sp. SUPER-H168 under high-level H\({}_{2}\)O\({}_{2}\). The results illustrated that hypocrellin yield was improved by approximately 27% and 25% post 72 h incubation with 10 mM and 20 mM H\({}_{2}\)O\({}_{2}\), respectively. Aside from oxidative agents, light can also affect hypocrellin production as well as growth and reproduction of _Shiraia_ sp. SUPER-H168. All incubations under different light (white, red, yellow, green, blue, and purple) conditions were beneficial to aerial hyphal growth as compared to darkness. In contrast, all light conditions examined inhibited hypocrellin biosynthesis, with the strongest inhibition displayed by blue light [103]. The mycelial culture of _S. bambusicola_ without illumination is a biotechnological alternative for hyporellin production but accompanied by the low yield. Recent investigation using a light/dark shift (24 h/24 h) regime showed that such illumination treatment not only elevated the hypocrellin level in mycelia by 65%, but also promoted its release into the medium, with the highest total hyporellin production (181.67 mg/L) on day 8, approximately a 73% rise in comparison to the dark controls. Moreover, light/dark shift was observed to elicit the formation of smaller and more compact fungal pellets without any growth retardation of mycelia, pinpointing a novel promising strategy for large-scale production of hypocrellin in mycelium cultures. Furthermore, the light/dark shift regime upregulated the expression of two reactive oxygen species (ROS)-related genes, including NADPH oxidase and cytochrome c peroxidase, and to induce ROS generation. It was also unveiled that ROS might be involved in the upregulation of key genes for hypocrellin biosynthesis and thereby promote hypocrellin production. Collectively, these results provide a molecular basis for deciphering the impacts of light/dark shift on fungal pigment production and for utilizing a tactical approach to increase hypocrellin production in submerged fermentation of _Shiraia_ species [104]. More recent studies with filamentous fungi in the genus _Aspergillus_ demonstrated that an increase in UV radiation could lead to a reduction in the _Aspergillus_ spp. population density in the field (vineyards, nuts, cereal crops). Moreover, it could unbalance the sporulating species present in the field, leading to an elevated prevalence of dark-pigmented conidia [105]. _Monascus_ pigments are a representative class of azaphilone pigments, commonly used in Asia since ancient times.