Signaling the Induction of Sporulation Involves the Interaction of Two Secondary Metabolites in <i>Aspergillus nidulans</i>

When growing <i>Aspergillus nidulans</i> hyphae encounter the atmosphere, they initiate a morphogenetic program leading to the production of spores. Mutants that are defective in the <i>fluG</i> gene fail to undergo sporulation because they lack an endogenous diffusible factor that purportedly accumulates on aerial hyphae, thus signaling the initiation of development. In this study, the defect could be reversed by adding culture extracts from a wild-type strain onto a mutant colony. Moreover, a bioassay-guided purification of the active culture extract resulted in the identification of the active agent as dehydroaustinol. However, this meroterpenoid was active only when administered in conjunction with the orsellinic acid derivative diorcinol. These two compounds formed an adduct that was detected by HRMS in an LC–MS experiment. The diorcinol-dehydroaustinol adduct prevented crystal formation of the signal on the surface of aerial hyphae and on an artificially prepared aqueous film and also increased the signal lipophilicity