A GntR family regulator HutC senses PCA to regulate histidine catabolism in <i>Pseudomonas aeruginosa</i>

Pathogenic bacteria, <i>Pseudomonas aeruginosa</i>, have evolved various regulatory mechanisms to cope with the adverse environments. HutC is associated with the regulation of histidine metabolism in bacteria. Despite extensive research on histidine metabolism, the identification of the HutC regulon is not systematic or comprehensive. In this study, we demonstrated that the <i>hut</i> operon including <i>hutFCHUIG</i> is involved in histidine catabolism in <i>P. aeruginosa</i>. We also identified that HutC participates in the regulation of histidine catabolism. Promoter activity measurement uncovered that HutC directly binds to the <i>hutFHUIG</i> promoter region and represses its transcription. Electrophoretic mobility shift assay with recombinant HutC showed that HutC directly represses the transcription of <i>hutIG</i>. More importantly, this inhibitory effect was relieved by the addition of phenazine-1-carboxylic acid. Collectively, these findings greatly expand our understanding of HutC as an important metabolic sensor for regulating Hut system in order to adapt to the harsh environments in <i>P. aeruginosa</i>.IMPORTANCEEnvironmental signaling molecules are pivotal mediators that enable bacteria to sense fluctuating environmental conditions, coordinate critical physiological processes including growth regulation, metabolic reprogramming, and virulence modulation. Our research elucidates two pivotal breakthroughs in bacterial environmental signal sensing mechanisms: First, we elucidated the regulatory mechanism of HutC in histidine catabolism through genetic and biochemical analysis. Second, utilizing untargeted metabolomics coupled with EMSA validation, we discovered PCA as a novel signaling molecule that interacts with HutC to modulate histidine catabolism. These findings not only expand our understanding of microbial cross-talk with environmental stimuli but also highlight its significance in both bacterial ecological adaptation and pathogenesis. The identification of PCA as a metabolic ligand opens new avenues for developing anti-infective strategies focused on bacterial signaling networks, while providing a methodological framework for uncovering latent environmental sensors in microbial communities.