Light responses of Monascus purpureus, a food grade biopigment producer

Introduction. Light is a critical environmental factor which can be considered as a stimulator, regulator, or inhibitor in several stages of the life cycle in several species. For fungi as non-photosynthetic microorganisms, it has been proved that presence of specific photoreceptor proteins sensitized them to light treatments, approximately around the visible spectrum, affecting cell growth and metabolism. Although its effect is noteworthy on microorganisms, most studies are focused on Neurospora crassa and Aspergillus nidulans. Monascus species are well-known traditional fungi in South East Asia for their ability to produce valuable secondary metabolites such as pigments, γ-aminobutyric acid, monacolins, and so on. For about two centuries, Monascus pigments have been widely used as food colorants; however, some strains of this genus are responsible for citrinin mycotoxin production threatening food safety. Materials & methods. In this work, M. purpureus PTCC 5303 was preserved as a pigment-producing fungus on sabouraud agar and let to grow for 7-10 days for spore formation. The fermentation medium contained (g/L) glucose 20, monosodium glutamate 3, KH2PO4 5, K2HPO4 5, MgSO4·7H2O 0.5, FeSO4·7H2O 0.01, ZnSO4·7H2O 0.01, KCl 0.5. The pH of the medium was adjusted at 6.5 prior to sterilization. The fungal strain was cultivated under both complete darkness and constant light (1500 lux) to evaluate its effect on fungal growth and secondary metabolite production. For estimation of different colors of light impact’s on pigment production, flasks with glucose-containing media were covered with optical red, green, and blue filters. Results & discussion. It was observed that pigment production under darkness was higher than white illumination. Also, it was monitored that green and blue filters resulted in higher cell growth in comparison with other conditions. Besides, the highest pigment productivity (28.7 AU410nm/g cell and 30.75 AU490nm/g cell) was achieved under green filter and it shows an approximate four-fold increase in comparison with dark condition. This response was attributed to the presence of phytochromes as photoreceptors. Phytochrome, traditionally confined to photosynthetic microorganisms, was recently discovered in heterotrophic fungi and based on these data, light is an important environmental signal for this fungus. However, further inclusive studies are crucial to clarify molecular pathway(s) responsible for evaluation of light effects on the genus Monascus. Conclusion. So far, some studies explore colors of light as an effective parameters on Monascus spp. metabolism but they indicated various responses to color spectrum can be obtained in time, intensity, and species-dependent manners.

کلیدواژه ها:

Biopigment ، light ، Monascus purpureus ، phytochrome.