Metabolic byproduct utilization and the evolution of mutually beneficial cooperation in Escherichia coli

Understanding how cooperation evolves in microbial populations,
particularly under environmental stress such as antibiotic exposure,
remains a key topic in evolutionary biology. Here, we investigate
cooperative interactions between antibiotic-resistant and
antibiotic-sensitive strains of Escherichia coli. Under antibiotic stress,
a small number of antibiotic-sensitive strains rapidly evolve into
antibiotic-resistant strains. Resistant E. coli produce indole, which
induces a protective response in sensitive cells, enabling them to survive
in antibiotic stress conditions. In turn, antibiotic-sensitive E. coli
could help reduce toxic accumulation of indole, indirectly benefiting the
resistant strain. Indole is harmful to the growth of the
antibiotic-resistant strain but benefits the antibiotic-sensitive strain
by helping turn-on the multi-drug exporter to neutralize the antibiotic.
This mutual exchange leads to increased fitness for both strains in
cocultures, demonstrating a mechanism by which mutually beneficial
cooperation can evolve in bacterial communities. Our findings provide
insight into how mutualism can emerge under antibiotic pressure through
metabolic byproduct exchange, revealing new dynamics in the evolution of
bacterial cooperation.