Riboflavin, overproduced during sporulation of Ashbya gossypii, protects its hyaline spores against ultraviolet light

Riboflavin (vitamin B-2), essential in tiny amounts as a precursor for oxid oreductase coenzymes, is a yellow pigment. Although it causes cytotoxicity via photoinduced damage of macromolecules, several microorganisms are strik ing overproducers. A question, unanswered for decades, is whether riboflavi n overproducers can benefit from this property. Here, we report an ultravio let (UV) protective effect of riboflavin. The spores of Ashbya gossypii, a riboflavin-overproducing fungus, are more sensitive to UV than those of Asp ergillus nidulans. The addition of riboflavin to suspensions improves the U V resistance of both spore types. Interestingly, we show that regulation of sporulation and riboflavin overproduction in A. gossypii are linked. In ba tch culture, both were elevated when growth ceased. At constant growth rate s, obtained in a chemostat culture, neither was elevated. Supplementation o f cultures by cAMP, a known stress signal, negatively affected sporulation as well as riboflavin overproduction, establishing a second, independent ar gument for the linkage.