4‐ H ydroxybenzoic acid is a diffusible factor that connects metabolic shikimate pathway to the biosynthesis of a unique antifungal metabolite in L ysobacter enzymogenes

Heat‐stable antifungal factor (HSAF) produced by Lysobacter enzymogenes is a potential lead compound for developing new antibiotics. Yet, how L. enzymogenes regulates the HSAF biosynthesis remains largely unknown. Here, we show that 4‐hydroxybenzoic acid (4‐HBA) serves as a diffusible factor for regulating HSAF biosynthesis. The biosynthesis of 4‐HBA involved an oxygenase, LenB2, and mutation of lenB2 almost completely abolished 4‐HBA production, leading to significantly impaired HSAF production. Introduction of a heterologous gene coding for 4‐HBA biosynthetic enzyme into the lenB2 mutant restored the production of 4‐HBA and HSAF to their corresponding wild‐type levels. Exogenous addition of 0.5–1 μM 4‐HBA was sufficient to restore HSAF production in the lenB2 mutant. Furthermore, the shikimate pathway was found to regulate the biosynthesis of HSAF via 4‐HBA. Finally, we identified a LysR‐family transcription factor (LysR Le ) with activity directed to HSAF production. LysR Le could bind to the HSAF promoter and, as a result, regulates expression of HSAF biosynthesis genes. The 4‐HBA could bind to LysR Le and appeared to partly enhance formation of the LysR Le –DNA complex . Collectively, our findings suggest that L. enzymogenes produces 4‐HBA to serve as an adaptor molecule to link the shikimate pathway to the biosynthesis of a unique antifungal metabolite (HSAF).