Transcriptional profiling of <i>Bordetella pertussis</i> reveals requirement of RNA chaperone Hfq for Type III secretion system functionality

<i>Bordetella pertussis</i>, the causative agent of human whooping cough (pertussis) produces a complex array of virulence factors in order to establish efficient infection in the host. The RNA chaperone Hfq and small regulatory RNAs are key players in posttranscriptional regulation in bacteria and have been shown to play an essential role in virulence of a broad spectrum of bacterial pathogens. This study represents the first attempt to characterize the Hfq regulon of the human pathogen <i>B. pertussis</i> under laboratory conditions as well as upon passage in the host and indicates that loss of Hfq has a profound effect on gene expression in <i>B. pertussis</i>. Comparative transcriptional profiling revealed that Hfq is required for expression of several virulence factors in <i>B. pertussis</i> cells including the Type III secretion system (T3SS). In striking contrast to the wt strain, T3SS did not become operational in the <i>hfq</i> mutant passaged either through mice or macrophages thereby proving that Hfq is required for the functionality of the <i>B. pertussis</i> T3SS. Likewise, expression of virulence factors <i>vag8</i> and <i>tcfA</i> encoding autotransporter and tracheal colonization factor, respectively, was strongly reduced in the <i>hfq</i> mutant. Importantly, for the first time we demonstrate that <i>B. pertussis</i> T3SS can be activated upon contact with macrophage cells <i>in vitro</i>.