MvaT binds to the P _exsC promoter to repress the type III secretion system in Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic human pathogen capable of causing a variety of acute and chronic infections. Its type III secretion system (T3SS) plays a critical role in pathogenesis during acute infection. ExsA is a master regulator that activates the expression of all T3SS genes. Transcription of exsA is driven by two distinct promoters, its own promoter P-exsA and its operon promoter P-exsC. Here, in combination with a DNA pull-down assay and mass spectrometric analysis, we found that a histone-like nucleoid-structuring (H-NS) family protein MvaT can bind to the P-exsC promoter. Using EMSA and reporter assays, we further found that MvaT directly binds to the P-exsC promoter to repress the expression of T3SS genes. The repression of MvaT on P-exsC is independent of ExsA, with MvaT binding to the -429 to -380 bp region relative to the transcription start site of the exsC gene. The presented work further reveals the complex regulatory network of the T3SS in P. aeruginosa.