Enteropathogenic Escherichia coli: identification of a gene cluster coding for bundle-forming pilus morphogenesis

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Enteropathogenic Escherichia coli (EPEC) utilizes virulence factors like bundle-forming pili (BFP) for host cell adhesion.
• Understanding the genetic basis of BFP biosynthesis is crucial for elucidating EPEC pathogenesis.

Purpose of the Study:

• To identify and characterize genes involved in the biosynthesis of bundle-forming pili (BFP) in EPEC.
• To investigate the genetic organization and conservation of the BFP gene cluster.

Main Methods:

• Sequence analysis of the region flanking the bfpA locus on the EPEC strain B171-8 plasmid.
• Deletion experiments to determine the functional role of identified open reading frames in BFP synthesis.
• Homology searches to identify related genes and functions.
• Restriction fragment length polymorphism (RFLP) analysis across multiple EPEC serotypes.

Main Results:

• Identification of a contiguous gene cluster of at least 12 open reading frames, including bfpA, essential for BFP filament synthesis.
• Discovery of genes within the cluster homologous to type IV pilus accessory genes, transformation competence, and protein secretion systems.
• Localization of a potential plasmid replication origin upstream of the BFP gene cluster, encoding replicase and resolvase homologs.
• Demonstration of conserved organization of the BFP gene cluster and its association with the replication origin across diverse EPEC serotypes.

Conclusions:

• The identified gene cluster is necessary and sufficient for the synthesis of morphologically normal BFP.
• The genetic organization of the BFP locus and its replication origin is a conserved feature of the EPEC biotype, suggesting a common evolutionary origin and functional importance.
• These findings provide insights into the molecular mechanisms of BFP production and EPEC virulence.