Weak Epistasis May Drive Adaptation in Recombining Bacteria.

Area of Science:

• Evolutionary biology
• Microbial genetics

Background:

• Recombination impacts epistasis in multi-locus trait evolution.
• High recombination in eukaryotes limits epistasis' role in short-term adaptation.
• Bacterial recombination rates vary, with some species exhibiting panmixia.

Purpose of the Study:

• To investigate if bacterial recombination limits selection on epistatic fitness contributions.
• To quantify homologous recombination in five bacterial pathogens.
• To model bacterial evolution with additive and epistatic effects using estimated recombination rates.

Main Methods:

• Quantification of homologous recombination rates in five bacterial pathogens.
• Development of a multilocus model for bacterial evolution.
• Inclusion of additive and epistatic effects within the evolutionary model.

Main Results:

• Selection on weak epistasis between distant mutations remains efficient in highly recombining bacteria (e.g., Streptococcus pneumoniae, Helicobacter pylori).
• Homologous recombination typically transfers short DNA segments, preserving selection efficiency.
• Strong epistasis accelerates bacterial selection, with dynamics influenced by recombination levels and locus number.

Conclusions:

• Epistasis plays a crucial role in both short- and long-term bacterial adaptive evolution.
• Unlike in eukaryotes, bacterial epistasis is not restricted to strong effects, linked loci, or specific conditions.
• Bacterial recombination dynamics can enhance, rather than limit, the impact of epistasis on evolution.