The RNA Chaperone Hfq Is Required for Virulence of Bordetella pertussis

Bordetella pertussis is a Gram-negative pathogen causing the human respiratory disease called pertussis or whooping cough. Here we examined the role of the RNA chaperone Hfq in B. pertussis virulence. Hfq mediates interactions between small regulatory RNAs and their mRNA targets and thus plays an important role in posttranscriptional regulation of many cellular processes in bacteria, including production of virulence factors. We characterized an hfq deletion mutant (Delta hfq) of B. pertussis 18323 and show that the Delta hfq strain produces decreased amounts of the adenylate cyclase toxin that plays a central role in B. pertussis virulence. Production of pertussis toxin and filamentous hemagglutinin was affected to a lesser extent. In vitro, the ability of the Delta hfq strain to survive within macrophages was significantly reduced compared to that of the wild-type (wt) strain. The virulence of the Delta hfq strain in the mouse respiratory model of infection was attenuated, with its capacity to colonize mouse lungs being strongly reduced and its 50% lethal dose value being increased by one order of magnitude over that of the wt strain. In mixedinfection experiments, the Delta hfq strain was then clearly outcompeted by the wt strain. This requirement for Hfq suggests involvement of small noncoding RNA regulation in B. pertussis virulence.