Asymmetric metabolic adaptations undermine stability in microbial syntrophy

Area of Science:

• Microbial Ecology
• Synthetic Biology
• Evolutionary Biology

Background:

• Syntrophic interactions, reliant on metabolite exchange, are common in microbial communities.
• Establishing stable metabolite exchange between auxotrophic microbes is challenging.
• Engineered auxotrophic Escherichia coli strains were used to study syntrophic dynamics.

Purpose of the Study:

• Investigate the stability and evolutionary dynamics of engineered microbial syntrophic relationships.
• Understand the factors contributing to the collapse of cooperative microbial consortia.
• Explore the role of metabolic plasticity and selfish phenotypes in microbial interactions.

Main Methods:

• Engineering two auxotrophic Escherichia coli strains for mutual amino acid dependence.
• Utilizing invasion-from-rare experiments to assess consortium formation and stability.
• Conducting laboratory evolution experiments over 25 days.
• Performing dynamic metabolic assays to analyze metabolite production and utilization.

Main Results:

• Rapid formation of syntrophic consortia stabilized by frequency-dependent selection, achieving a 2:1 lysine-to-arginine auxotroph ratio.
• Evolutionary instability leading to consortium collapse, with lysine-auxotroph (ΔL) cells dominating.
• Emergence of a 'selfish' ΔL phenotype with reduced arginine production and exploitation of lysine.
• Metabolic plasticity in ΔL cells allowed adaptation to lysine availability, enabling competitive exclusion of arginine-auxotroph (ΔA) cells.

Conclusions:

• Asymmetric metabolic responses and the evolution of selfish phenotypes destabilize microbial syntrophy.
• Balanced metabolic exchange is crucial for the sustainability of synthetic microbial consortia.
• The study provides insights into the evolutionary mechanisms governing microbial cooperation and conflict.