The transcriptional regulator Lrp activates the expression of genes involved in tilivalline enterotoxin biosynthesis in Klebsiella oxytoca

The toxigenic Klebsiella oxytoca strains secret the tilivalline enterotoxin, which causes antibiotic-associated hemorrhagic colitis. The tilivalline is a non-ribosomal peptide synthesized by enzymes encoded in two divergent operons clustered in a pathogenicity island. The transcriptional regulator Lrp (leucine-responsive regulatory protein) controls the expression of several bacterial genes involved in virulence. In this work, we determined the transcriptional expression of aroX and npsA, the first genes of each tilivalline biosynthetic operon in K. oxytoca MIT 09-7231 wild-type and its derivatives Dlrpmutant and complemented strains. The results show that Lrp directly activates the transcription of both aroX and npsAgenes by binding to the intergenic regulatory region in a leucine-dependent manner. Furthermore, the lack of Lrp significantly diminished the cytotoxicity of K. oxytoca on HeLa cells due to tilivalline reduced production. Altogether, our data highlight Lrp as a new regulator by which cytotoxin-producing K. oxytoca strains control the expression of genes involved in the biosynthesis of their main virulence factor.