Eikenella corrodens phase variation involves a posttranslational event in pilus formation

Area of Science:

• Microbiology
• Molecular Biology
• Bacterial Pathogenesis

Background:

• Eikenella corrodens, a human pathogen, exhibits phase variation.
• This variation involves a switch between piliated (S-phase, small colonies) and nonpiliated (L-phase, large colonies) variants.
• The molecular mechanisms underlying this phenotypic change remain largely uncharacterized.

Purpose of the Study:

• To investigate the molecular basis of phase variation in Eikenella corrodens.
• To identify genetic elements and regulatory mechanisms controlling type IV pilus synthesis and assembly.

Main Methods:

• Cloning and sequencing of the major type IV pilin gene locus (pilA locus) from S-phase variants.
• DNA hybridization and Northern blot analysis to compare gene locus and transcript abundance between S- and L-phase variants.
• Electron microscopy and immunochemical analysis to assess pilin synthesis, export, and assembly.

Main Results:

• The pilA locus, containing pilA1, pilA2, pilB, and hagA ORFs, was identical in both S- and L-phase variants.
• Transcription of the pilA locus was similar between phases, with abundant and read-through transcripts detected.
• S-phase variants successfully synthesized, exported, and assembled pilin into type IV pili.
• L-phase variants synthesized pilin but failed to export and assemble it into pili.

Conclusions:

• Phase variation in Eikenella corrodens is not due to alterations in the pilA locus sequence or transcription levels.
• The switch is likely regulated at a post-translational level, specifically affecting pilin export and assembly.
• This post-translational control mechanism is crucial for the phenotypic switching observed in E. corrodens.