Recombination may enhance adaptation for bacterial populations by alleviating competition among clonal lineages carrying different beneficial mutations (clonal interference), and by freeing beneficial mutations from deleterious genetic backgrounds. This benefit of recombination, known as the Fisher-Muller model, is a leading explanation for the prevalence of sexual reproduction in eukaryotes and has been proposed as an evolutionary benefit of genetic exchange in bacteria.
To test for an evolutionary benefit of recombination in bacteria adapting to new environments, we used experimental evolution and whole-genome sequencing with Acinetobacter baylyi (which exchange genes via natural transformation). Naturally competent and genetically constructed, non-competent populations were experimentally evolved for 800 generations, in novel media conditions. The extent of adaptation was assessed using competitive fitness assays and beneficial mutations were sought by comparing ancestral and evolved genomes.
Results show that both competent and non-competent bacterial populations adapted to similar extents, and no benefits of recombination were found. Subsequent whole genome sequencing revealed only few candidate adaptive mutations, indicating that adaptation may have been mutation limited (for both types of bacteria). If few beneficial mutations were available to evolving populations, this may explain why there was no apparent benefit to recombination, as the benefits of recombination require that multiple mutations be present concurrently within evolving populations. While previous studies have reported enhanced adaptation of recombining populations, the current results indicate that the conditions under which recombination can enhance bacterial evolution are limited.