Abstract

In single-cell microbes, primary and secondary metabolism are synergistically integrated to support survival and environmental adaptation through the biosynthesis of structurally diverse and biologically active small molecules-known as secondary metabolites (SMs) or natural products, such as penicillin. However, the therapeutic potential of microbial SMs is often limited because their biosynthetic gene clusters remain silent or weakly expressed under laboratory conditions. In this study, we employed BioNavi-NP as a guide to identify heme A synthase (ClHAS) as a novel metabolic link in Curvularia lunata, bridging primary and secondary metabolism. Surprisingly, inactivation of ClHAS led to the diversification of its characteristic indolizidine alkaloids, yielding previously unreported molecular frameworks. Mechanistically, ClHAS disruption impaired heme biosynthesis, thereby inducing oxidative stress that activated an uncharacterized basic-region leucine zipper transcription factor (A7370). A7370 binds specifically to a unique cis-element (ACGGCTGAC) in the promoter region of cuaF, a pathway-specific positive regulator of indolizidine alkaloid biosynthesis. This cascade regulation produces structurally unprecedented alkaloids, some of which show antibacterial activity equal or superior to the clinically prescribed drug, tinidazole, against a range of human pathogenic bacteria. Overall, this work reveals a conserved regulatory network that coordinates primary and secondary metabolism in fungi, providing new mechanistic insights into the complexity of fungal SM biosynthesis.