When Ratcliff and his team mixed two strains of Vibrio cholerae bacteria with different T6SS toxins on petri dishes, one strain or the other always killed off its opponent at any given place. The two strains gradually separated into patches of one strain or the other, just like a thin film of oil and water separates into pure droplets.
This separation, or population structure, should allow cooperators to share their secretions only with other similar cells, which would increase the survival of those cells and mean cooperation would be evolutionarily advantageous.
To probe whether that is true in the real world, the team examined the genomes of 439 species of bacteria, counting both the number of T6SS toxins – a measure of how aggressively they kill bacteria unlike themselves – and the number of secreted gene products, a measure of their level of cooperation. Sure enough, species with more T6SS produce more secreted products.
Lethal competition may make cooperation more likely to evolve in other organisms as well, such as plants that secrete toxins into the surrounding soil. “Localised warfare is a pretty general route to generating structured populations, which itself is a general route to evolving cooperation with relatives,” says Ratcliff.
Vicious microbial warfare helps bacteria evolve cooperation – New Scientist
