Herd immunity underlies homologous recombination in stationary phase bacteria.

Herd immunity in stationary-phase Escherichia coli promotes homologous recombination, increasing gene flow by up to two orders of magnitude compared to spontaneous mutation.

• Why it matters: Understanding how bacteria sustain high rates of homologous recombination is crucial for revealing mechanisms of genetic diversity and evolution in microbial populations, especially under conditions where mutation supply is limited.
• What they did: The study used an E. coli-P1 phage model system to show that herd immunity maintains phage-susceptible bacteria, immune bacteria, and transducing phages, facilitating recombination that depends on recA, recB, and recG, and can be reinitiated by nutrient pulses.
• The result: This work suggests bacterial herd immunity can act as an evolutionary driver by enabling phages to serve as genetic vectors, thereby shaping molecular evolution and maintaining high recombination rates in bacterial populations.