XRE-type transcriptional regulator ProR controls prodigiosin synthesis in Serratia marcescens JNB5-1

The gram-negative bacterium <i>Serratia marcescens</i> produces various secondary metabolites, including prodigiosin, althiomycin, and serratamolide. Among these, prodigiosin exhibits multiple biological activities such as antibacterial, anticancer, and immunosuppressive properties. Nevertheless, our understanding of the regulatory mechanisms governing prodigiosin biosynthesis in <i>S. marcescens</i> remains incomplete. Here, an HTH_XRE family transcription factor, BVG90_RS12600 (designated ProR), was identified as a positive regulator of prodigiosin production. Disruption of <i>proR</i> drastically reduced prodigiosin yield, with the Δ<i>proR</i> mutant producing only 2.68% of that produced by the wild-type strain JNB5-1. Integrated analysis employing comparative transcriptomics, RT-qPCR, electrophoretic mobility shift assays (EMSA), and transcriptional fusion reporters elucidated the molecular mechanism whereby ProR regulates prodigiosin biosynthesis in <i>S. marcescens</i>. Mechanistically, ProR binds to the promoter region of <i>psrA</i>, which encodes a key transcriptional activator of prodigiosin synthesis, thereby upregulating PsrA expression. This, in turn, enhances transcription of the prodigiosin biosynthetic (<i>pig</i>) operon, establishing ProR as a positive regulator in the prodigiosin biosynthesis pathway. Our findings provide a framework for systematically elucidating the complex regulatory network governing prodigiosin biosynthesis in <i>S. marcescens</i> and for rational engineering of optimized microbial chassis for its overproduction.