Destruxins are cyclic hexadepsipeptides with a broad bioactivity spectrum, including insecticidal, phytotoxic, antiviral, antimicrobial, and anticancer properties, making them highly valuable metabolites in agriculture, medicine, and biotechnology. Due to their critical role in insect-fungal and plant-fungal interactions, understanding the environmental factors triggering their production is of high interest. This study examined whether different light wavelengths affect the production of the destruxins A, B, and E in Metarhizium brunneum BIPESCO 5, and whether any light effect was independent of the nutritional state of the culture. To achieve this, M. brunneum was grown in bioreactor batch cultures using two different media (i.e., nutrient-rich Sabouraud-4 %-glucose (S4G) medium versus nitrogen-limited (N-lim) minimal medium). Five illumination conditions were applied to each tested medium, comprising either constant darkness, or red light (660 ± 25 nm), green light (528 ± 33 nm), or blue light (455 ± 20 nm) at an intensity of 1.4 mW cm-2 as well as UV-A (340/375 + 11 nm) irradiation at an intensity of 1.1 mW cm-2. Destruxin production proved to be affected by the illumination conditions, with distinct light responses depending on the medium composition. Overall, cultures grown in the N-lim minimal medium exhibited significantly higher destruxin A and B concentrations compared to those in the nutrient-rich S4G medium. Shorter wavelengths (UV-A, blue, and green light) enhanced destruxin A and B production in the S4G medium but reduced their levels in the N-lim medium, whereby the destruxin A:B ratios remained constant within each nutritional condition. This study adds to the growing evidence of complex, nutrient-dependent light responses in fungal secondary metabolism, suggesting that destruxin biosynthesis is a finely tuned adaptive mechanism, possibly as a tool for niche exploitation, rather than a simple on/off metabolic reaction.
Schobert et al. (Wed,) studied this question.