Oosporein is a purple-red pigment published as a metabolite of Acremonium sp. in 1959. Oosporein has antibacterial, antiviral and antifungal activity. Oosporein is produced by the entomopathogenic fungus Beauveria bassiana after host death, acting to limit microbial competition on B. bassiana-killed hosts and allowing the fungus to maximally use host nutrients to grow and sporulate on infected insect cadavers. Oosporein production is regulated by a cascade of transcription factors, with BbSmr1 acting as an upstream negative regulator, targeting the expression of OpS3, which in turn acts as a positive regulator of the oosporein biosynthetic gene cluster.