Integration host factor is required for the DNA inversion that controls phase variation in Escherichia coli

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Type 1 fimbriae expression in Escherichia coli exhibits phase variation, controlled by DNA inversion.
• This inversion process is mediated by specific genes and requires regulatory factors.

Purpose of the Study:

• To investigate the role of integration host factor (IHF) in the phase variation of type 1 fimbriae.
• To elucidate the mechanism by which IHF regulates fimA gene expression.

Main Methods:

• Utilized gene deletion and inactivation (himA, hip/himD) in E. coli strains with fimA-lacZ operon fusions.
• Employed Southern hybridization to analyze genetic rearrangements.
• Restored IHF function using a himA+ plasmid.

Main Results:

• himA or hip/himD mutations significantly reduced phase variation rates from 10(-3) to <10(-5) per cell per generation.
• IHF-deficient mutants failed to undergo the switch-generated genetic rearrangement.
• Complementation with himA+ restored normal phase variation.

Conclusions:

• Integration host factor (IHF) is indispensable for normal type 1 fimbriae phase variation in E. coli.
• IHF mediates the DNA inversion required for regulating fimbrial gene expression and bacterial adhesion.