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Journal of Bacteriology, January 2001, p. 55-62, Vol. 183, No. 1
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.1.55-62.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Role of the Eikenella corrodens pilA Locus in Pilus Function and Phase Variation

Maria T. Villar, Rona L. Hirschberg,dagger and Michael R. Schaefer*

Division of Molecular Biology and Biochemistry, School of Biological Sciences, University of Missouri---Kansas City, Kansas City, Missouri 64110

Received 20 June 2000/Accepted 12 October 2000

The human pathogen Eikenella corrodens expresses type IV pili and exhibits a phase variation involving the irreversible transition from piliated to nonpiliated variants. On solid medium, piliated variants form small (S-phase), corroding colonies whereas nonpiliated variants form large (L-phase), noncorroding colonies. We are studying pilus structure and function in the clinical isolate E. corrodens VA1. Earlier work defined the pilA locus which includes pilA1, pilA2, pilB, and hagA. Both pilA1 and pilA2 predict a type IV pilin, whereas pilB predicts a putative pilus assembly protein. The role of hagA has not been clearly established. That work also confirmed that pilA1 encodes the major pilus protein in this strain and showed that the phase variation involves a posttranslational event in pilus formation. In this study, the function of the individual genes comprising the pilA locus was examined using a recently developed protocol for targeted interposon mutagenesis of S-phase variant VA1-S1. Different pilA mutants were compared to S-phase and L-phase variants for several distinct aspects of phase variation and type IV pilus biosynthesis and function. S-phase cells were characterized by surface pili, competence for natural transformation, and twitching motility, whereas L-phase cells lacked these features. Inactivation of pilA1 yielded a mutant that was phenotypically indistinguishable from L-phase variants, showing that native biosynthesis of the type IV pilus in strain VA1 is dependent on expression of pilA1 and proper export and assembly of PilA1. Inactivation of pilA2 yielded a mutant that was phenotypically indistinguishable from S-phase variants, indicating that pilA2 is not essential for biosynthesis of functionally normal pili. A mutant inactivated for pilB was deficient for twitching motility, suggesting a role for PilB in this pilus-related phenomenon. Inactivation of hagA, which may encode a tellurite resistance protein, had no effect on pilus structure or function.

* Corresponding author. Mailing address: University of Missouri---Kansas City, School of Biological Sciences, 5100 Rockhill Road, Kansas City, MO 64110. Phone: (816) 235-2573. Fax: (816) 235-5595. E-mail: schaeferm{at}umkc.edu.

dagger Present address: Center for Scientific Review, National Institutes of Health, Bethesda, MD 20892.

Journal of Bacteriology, January 2001, p. 55-62, Vol. 183, No. 1
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.1.55-62.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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Copyright © 2001 by the American Society for Microbiology. All rights reserved.