Innovation in an E. coli evolution experiment is contingent on maintaining adaptive potential until competition...

Area of Science:

• Evolutionary biology
• Microbial evolution
• Genetics

Background:

• Key innovations allow species to rapidly diversify by overcoming environmental constraints.
• The Lenski long-term evolution experiment tracks Escherichia coli populations over generations.
• Citrate utilization evolved in only one of twelve E. coli populations, despite citrate being an abundant resource.

Purpose of the Study:

• Investigate the genetic and ecological factors hindering the evolution of citrate utilization in Escherichia coli.
• Determine why citrate utilization took so long to evolve in the Lenski experiment.
• Understand the evolutionary trajectory leading to this key innovation.

Main Methods:

• Recapitulated the initial mutation for citrate utilization in E. coli strains from the first 31,500 generations.
• Analyzed fitness benefits and costs associated with early mutations.
• Examined the genetic background's influence on the evolution of citrate utilization.

Main Results:

• An initial mutation conferring a slight fitness benefit was present early on but was initially blocked by competition.
• An anti-potentiated genetic background later made rudimentary citrate utilization deleterious.
• Citrate utilization evolved only after mutations restored the initial mutation's benefit and adaptation slowed.

Conclusions:

• Intense competition and favored mutations can create short-sighted evolutionary paths.
• This can obscure crucial stepping-stone mutations needed for key innovations.
• Understanding these dynamics is vital for predicting evolutionary trajectories.