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Journal of Bacteriology, April 2007, p. 3198-3207, Vol. 189, No. 8
0021-9193/07/$08.00+0     doi:10.1128/JB.01833-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

pilQ Missense Mutations Have Diverse Effects on PilQ Multimer Formation, Piliation, and Pilus Function in Neisseria gonorrhoeae{triangledown}

R. Allen Helm, Michelle M. Barnhart,{dagger} and H. Steven Seifert*

Northwestern University, Feinberg School of Medicine, Department of Microbiology-Immunology, Chicago, Illinois

Received 6 December 2006/ Accepted 29 January 2007

Type IV pili are required for virulence in Neisseria gonorrhoeae, as they are involved in adherence to host epithelium, twitching motility, and DNA transformation. The outer membrane secretin PilQ forms a homododecameric ring through which the pilus is proposed to be secreted. pilQ null mutants are nonpiliated, and thus, all pilus-dependent functions are eliminated. Mutagenesis was performed on the middle one-third of pilQ, and mutants with colony morphologies consistent with the colony morphology of nonpiliated or underpiliated bacteria were selected. Nineteen mutants, each with a single amino acid substitution, were isolated and displayed diverse phenotypes in terms of PilQ multimer stability, pilus expression, transformation efficiency, and host cell adherence. The 19 mutants were grouped into five phenotypic classes based on functionality. Four of the five mutant classes fit the current model of pilus functionality, which proposes that a functional pilus assembly apparatus, not necessarily full-length pili, is required for transformation, while high levels of displayed pili are required for adherence. One class, despite having an underpiliated colony morphology, expressed high levels of pili yet adhered poorly, demonstrating that pilus expression is necessary but not sufficient for adherence and indicating that PilQ may be directly involved in host cell adherence. The collection of phenotypes expressed by these mutants suggests that PilQ has an active role in pilus expression and function.

* Corresponding author. Mailing address: Department of Microbiology-Immunology, Northwestern University's Feinberg School of Medicine, S213, 303 East Chicago Avenue, Chicago, IL 60611. Phone: (312) 503-9788. Fax: (312) 503-1339. E-mail: h-seifert{at}northwestern.edu

{triangledown} Published ahead of print on 2 February 2007.

{dagger} Present address: University of Michigan, Department of Molecular, Cellular, and Developmental Biology, 830 North University, Ann Arbor, MI 48109.

Journal of Bacteriology, April 2007, p. 3198-3207, Vol. 189, No. 8
0021-9193/07/$08.00+0     doi:10.1128/JB.01833-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.





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