Histamine activates HinK to promote the virulence of Pseudomonas aeruginosa

When histamine is present, HinC together with HinD catalyses the conversion of histamine to ImAA, which in turn acts as an inducer, binds to HinK and activates its transcriptional regulatory activity against genes involved in histamine utilization (i.e., hinK, hinDAC-pa0222 operon, and hinFLHG operon) and those associated with the pathogenicity of P. aeruginosa (e.g., pqsABCDE operon and pvdS). These findings suggest that histamine acts as an interkingdom signal and provide insights into the mechanism used by pathogenic bacteria to exploit host regulatory signals to promote virulence.