Eikenella corrodens phase variation involves a posttranslational event in pilus formation.
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.
Villar
M T
MT
Division of Molecular Biology and Biochemistry, School of Biological Sciences, University of Missouri-Kansas City, Kansas City, Missouri 64110, USA.
Helber
J T
JT
Hood
B
B
Schaefer
M R
MR
Hirschberg
R L
RL
D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D003001:Cloning, Molecular; D004269:DNA, Bacterial / Q000032:analysis; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D016124:Eikenella corrodens / Q000235:genetics* / Q000254:growth & development* / Q000378:metabolism / Q000648:ultrastructure; D036781:Fimbriae Proteins; D010861:Fimbriae, Bacterial / Q000378:metabolism*; D016905:Gram-Negative Bacterial Infections / Q000382:microbiology; D006801:Humans; D015151:Immunoblotting; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D009693:Nucleic Acid Hybridization; D011499:Protein Processing, Post-Translational; D017422:Sequence Analysis, DNA; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D036781:Fimbriae Proteins