Effects of Blue Light on Hypocrellin A Production in Shiraia Mycelium Cultures

Blue light is a crucial environmental cue for fungi. Hypocrellin A (HA) is a photoactive perylenequinone from Shiraia with strong antimicrobial and anticancer properties. In this study, effects of the illumination of blue-light-emitting diode (LED) at 470 nm on Shiraia sp. S8 were investigated. Blue light at 50-200 lx and 4-6 h day^-1 could enhance HA content in the mycelia, but suppress it at 300-400 lx or with longer exposure (8-24 h day^-1 ). The intermittent blue light (6 h day^-1 ) at 200 lx not only enhanced the fungal conidiation but also stimulated HA production without any growth retardation. The generation of fungal reactive oxygen species was induced to upregulate HA biosynthetic gene expressions. When the culture was maintained under the intermittent blue light for 8 days, HA production reached 242.76 mg L^-1 , 2.27-fold of the dark control. On the other hand, both the degradation of HA and downregulation of HA biosynthetic genes occurred under long exposure time (8-24 h day^-1 ), leading to the suppression of HA production. These results provide a basis for understanding the regulation of blue light on the biosynthesis of fungal photoactivated perylenequinones, and the application of a novel light elicitation to Shiraia mycelium cultures for enhanced HA production.