Evolution of a bistable genetic system in fluctuating and nonfluctuating environments

Area of Science:

• Microbiology
• Evolutionary Biology
• Genetics

Background:

• Epigenetic mechanisms enable bacterial phenotypic switching, crucial for adaptation in dynamic environments.
• Mathematical models suggest epigenetic switches are adaptive, but experimental validation is limited.
• Phenotypic heterogeneity can be an evolutionary advantage in unpredictable conditions.

Purpose of the Study:

• To experimentally investigate the role of the opvAB operon epigenetic switch in Salmonella enterica adaptation.
• To determine if OpvAB bistability provides a survival advantage in fluctuating environments.
• To provide empirical support for theoretical models of epigenetic adaptation.

Main Methods:

• Utilized Salmonella enterica and its opvAB operon, which controls epigenetic switching.
• Conducted bacterial evolution experiments under changing and stable environmental conditions.
• Employed computational simulations to model epigenetic variation and its adaptive value.

Main Results:

• Demonstrated that OpvAB bistability (OpvAB^OFF/phage-sensitive and OpvAB^ON/phage-resistant) is maintained in changing environments but not stable ones.
• Showcased the reversible nature of the OpvAB epigenetic switch.
• Observed that phenotypic heterogeneity conferred by the switch acts as a bet-hedging strategy.

Conclusions:

• Epigenetic variation, exemplified by the opvAB operon, is a key evolutionary strategy for mutation avoidance in fluctuating environments.
• The OpvAB switch in Salmonella preadapts populations to phage encounters through bet-hedging.
• Experimental findings support game theory models on the benefits of phenotypic heterogeneity in unpredictable environments.