Bordetella pertussis Can Be Motile and Express Flagellum-Like Structures

Abstract

<i>Bordetella bronchiseptica</i> encodes and expresses a flagellar apparatus. In contrast, <i>Bordetella pertussis</i>, the causative agent of whooping cough, has historically been described as a nonmotile and nonflagellated organism. The previous statements that <i>B. pertussis</i> was a nonmotile organism were consistent with a stop codon located in the flagellar biosynthesis gene, <i>flhA</i>, discovered when the <i>B. pertussis</i> Tohama I genome was sequenced and analyzed by Parkhill et al. in 2003 (J. Parkhill, M. Sebaihia, A. Preston, L. D. Murphy, et al., Nat Genet, 35:32-40, 2003, https://doi.org/10.1038/ng1227). The stop codon has subsequently been found in all annotated genomes. Parkhill et al. also showed, however, that <i>B. pertussis</i> contains all genetic material required for flagellar synthesis and function. We and others have determined by various transcriptomic analyses that these flagellar genes are differentially regulated under a variety of <i>B. pertussis</i> growth conditions. In light of these data, we tested for <i>B. pertussis</i> motility and found that both laboratory-adapted strains and clinical isolates can be motile. Upon isolation of motile <i>B. pertussis</i>, we discovered flagellum-like structures on the surface of the bacteria. <i>B. pertussis</i> motility appears to occur primarily in the Bvg(-) phase, consistent with regulation present in <i>B. bronchiseptica</i> Motility can also be induced by the presence of fetal bovine serum. These observations demonstrate that <i>B. pertussis</i> can express flagellum-like structures, and although it remains to be determined if <i>B. pertussis</i> expresses flagella during infection or if motility and/or flagella play roles during the cycle of infection and transmission, it is clear that these data warrant further investigation.<b>IMPORTANCE</b> This report provides evidence for motility and expression of flagella by <i>B. pertussis</i>, a bacterium that has been reported as nonmotile since it was first isolated and studied. As with <i>B. bronchiseptica</i>, <i>B. pertussis</i> cells can express and assemble a flagellum-like structure on their surface, which in other organisms has been implicated in several important processes that occur <i>in vivo</i> The discovery that <i>B. pertussis</i> is motile raises many questions, including those regarding the mechanisms of regulation for flagellar gene and protein expression and, importantly, the role of flagella during infection. This novel observation provides a foundation for further study of <i>Bordetella</i> flagella and motility in the contexts of infection and transmission.