Limits to the evolution of metabolic dependency in spatially structured microbial communities

Area of Science:

• Microbial Ecology
• Evolutionary Biology
• Systems Biology

Background:

• Evolutionary processes can lead to gene loss in microbial communities, creating metabolic dependencies.
• The Black Queen Hypothesis posits that gene loss offers a fitness advantage by reducing metabolic burden.

Purpose of the Study:

• To investigate the evolution of metabolic dependencies in spatially structured microbial communities at the single-cell level.
• To understand the invasion fitness of auxotrophic mutants in relation to nutrient exchange with wildtype neighbors.

Main Methods:

• Microfluidic single-cell imaging to observe microbial populations.
• Mathematical modeling to analyze mutant dynamics and nutrient dependencies.

Main Results:

• Auxotroph growth is constrained by limited amino acid leakage from wildtype neighbors.
• Local clustering of auxotrophs exacerbates growth limitations by depleting the shared nutrient pool.
• A growth advantage for auxotrophs was observed only with external amino acid supplementation or high wildtype leakage.

Conclusions:

• Metabolic dependencies and nutrient exchange dynamics significantly impact mutant invasion fitness.
• There is a trade-off between reducing metabolic costs via gene loss and maintaining metabolic autonomy.