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Journal of Bacteriology, July 1999, p. 4154-4160, Vol. 181, No. 14
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Eikenella corrodens Phase Variation Involves a Posttranslational Event in Pilus Formation

Maria T. Villar, Jennifer T. Helber, Becky Hood, Michael R. Schaefer,* and Rona L. Hirschbergdagger

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

Received 3 February 1999/Accepted 4 May 1999

The human pathogen Eikenella corrodens synthesizes 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 the molecular basis of this phase variation in the clinical isolate E. corrodens VA1. A genomic fragment encoding the major type IV pilin was cloned from the S-phase variant of strain VA1. Sequence analysis of the fragment revealed four tandemly arranged potential open reading frames (ORFs), designated pilA1, pilA2, pilB, and hagA. Both pilA1 and pilA2 predict a type IV pilin. The protein predicted by pilB shares sequence identity with the Dichelobacter nodosus FimB fimbrial assembly protein. The protein predicted by hagA resembles a hemagglutinin. The region containing these four ORFs was designated the pilA locus. DNA hybridization and sequence analysis showed that the pilA locus of an L-phase variant of strain VA1 was identical to that of the S-phase variant. An abundant pilA1 transcript initiating upstream of pilA1 and terminating at a predicted hairpin structure between pilA1 and pilA2 was detected by several assays, as was a less abundant read-through transcript encompassing pilA1, pilA2, and pilB. Transcription from the pilA locus was nearly indistinguishable between S- and L-phase variants. Electron microscopy and immunochemical analysis showed that S-phase variants synthesize, export, and assemble pilin into pili. In contrast, L-phase variants synthesize pilin but do not export and assemble it into pili. These data suggest that a posttranslational event, possibly involving an alteration in pilin export and assembly, is responsible for phase variation in E. corrodens.

* 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, July 1999, p. 4154-4160, Vol. 181, No. 14
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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