Detecting selective sweeps in naturally occurring Escherichia coli

Area of Science:

• Microbiology
• Evolutionary Biology
• Genetics

Background:

• Escherichia coli (E. coli) is a globally significant bacterium.
• Understanding genetic variation is crucial for tracking bacterial evolution and adaptation.
• The gapA and pabB genes are important targets for evolutionary studies.

Purpose of the Study:

• To investigate the evolutionary forces shaping genetic diversity in E. coli.
• To analyze nucleotide sequences of gapA and pabB genes in natural isolates.
• To determine if recent evolutionary events have impacted genetic variability.

Main Methods:

• Sequencing of gapA and pabB genes in 12 E. coli isolates.
• Comparative analysis of polymorphism levels within and between E. coli and Salmonella.
• Application of the Hudson-Kreitman-Aguadé (HKA) test for selective neutrality.
• Examination of gene genealogies for topological consistency.

Main Results:

• Evidence suggests a recent evolutionary event has purged variability around gapA and pabB loci in E. coli.
• The Hudson-Kreitman-Aguadé (HKA) test indicated non-neutral evolution.
• Gene genealogies showed topological inconsistencies, supporting a recent selective sweep.
• Reduced genetic variability was observed in the vicinity of the studied genes.

Conclusions:

• Directional selection has likely driven the spread of a beneficial allele in E. coli.
• Genetic hitchhiking has resulted in a loss of variability in surrounding genomic regions.
• These findings provide insight into the recent evolutionary history of E. coli populations.