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Demonstration of Type IV Pilus Expression and a Twitching Phenotype by Haemophilus influenzae

Department of Pediatrics, Center for Microbial Pathogenesis, Columbus Children's Research Institute, The Ohio State University College of Medicine and Public Health, Columbus, Ohio¹

Received 17 August 2004/ Returned for modification 29 September 2004/ Accepted 12 November 2004

Haemophilus influenzae is considered a nonmotile organism that expresses neither flagella nor type IV pili, although H. influenzae strain Rd possesses a cryptic pilus locus. We demonstrate here that the homologous gene cluster pilABCD in an otitis media isolate of nontypeable H. influenzae strain 86-028NP encodes a surface appendage that is highly similar, structurally and functionally, to the well-characterized subgroup of bacterial pili known as type IV pili. This gene cluster includes a gene (pilA) that likely encodes the major subunit of the heretofore uncharacterized H. influenzae-expressed type IV pilus, a gene with homology to a type IV prepilin peptidase (pilD) as well as two additional uncharacterized genes (pilB and pilC). A second gene cluster (comABCDEF) was also identified by homology to other pil or type II secretion system genes. When grown in chemically defined medium at an alkaline pH, strain 86-028NP produces approximately 7-nm-diameter structures that are near polar in location. Importantly, these organisms exhibit twitching motility. A mutation in the pilA gene abolishes both expression of the pilus structure and the twitching phenotype, whereas a mutant lacking ComE, a Pseudomonas PilQ homologue, produced large appendages that appeared to be membrane bound and terminated in a slightly bulbous tip. These latter structures often showed a regular pattern of areas of constriction and expansion. The recognition that H. influenzae possesses a mechanism for twitching motility will likely profoundly influence our understanding of H. influenzae-induced diseases of the respiratory tract and their sequelae.

* Corresponding author. Mailing address: Department of Pediatrics, Columbus Children's Research Institute, Center for Microbial Pathogenesis, The Ohio State University College of Medicine and Public Health, 700 Children's Dr., Columbus, OH 43205-2696. Phone: (614) 722-2915. Fax: (614) 722-2818. E-mail for Lauren O. Bakaletz: BakaletL{at}pediatrics.ohio-state.edu. E-mail for Robert S. Munson, Jr.: MunsonR{at}pediatrics.ohio-state.edu.

Editor: D. L. Burns

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