Global regulation of mediated by the histidine-responsive local transcription factor HutC in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a metabolically versatile environmental pathogen whose virulence relies on coordinated expression of catabolic genes, particularly the histidine utilization (hut) operon. Disruption of the hut operon reduces virulence, but the underlying mechanism remains rudimentary. Here, we genetically characterized the histidine-responsive transcriptional factor HutC in P. aeruginosa PAO1, alongside HutC in the non-pathogenic strain P. fluorescens SBW25. Two important features emerged. First, HutC recognizes two distinct DNA-binding motifs with little sequence similarity; notably, a noncanonical binding site was identified in the hutF promoter of SBW25 but was absent in PAO1. Second, HutC exhibits low-affinity binding to genes beyond histidine catabolism and contributes to the expression of multiple virulence traits. These findings identify HutC as a local regulator linking histidine catabolism with virulence and as a unique prokaryotic model for studying how noncanonical transcriptional factor-DNA interactions achieve binding specificity, a phenomenon so far investigated only in eukaryotes. Overall design: Compare trasncriptomes between wild-type PAO1 with each of three derived mutants with hutC expressed at different levels. Bacteria were gorwn on minimal medium supplemented with histidine (10 mM) as the sole source of carbon and nitrogen.