Although you might think that cheating is a phenomenon that is only observed in humans and other species with high-level cognitive functioning, a recent study by scientists from the Max Planck Society examined the presence of cooperative partnerships in bacteria that limit the access of nutrients of non-cooperative bacteria. In these microbial communities, different species of bacteria exchange nutrients and feed other bacterial cells in the environment. However, the bacteria that do not contribute to this cooperative nutrient production are spatially excluded when these cross-feeding interactions occur on two-dimensional surfaces.
The reciprocal exchange of nutrients among bacteria saves them the energy that it would cost to produce them individually, which limits their energy production and can have a positive effect on bacterial growth. In contrast, when non-cooperating bacteria consume without providing anything in return, they put this beneficial evolutionary relationship at risk, which is why bacteria evolved a method of spatially excluding them.
"The fact that such a simple principle can effectively stabilize such a complex interaction suggests that similar phenomena may play important roles in natural bacterial communities," Christian Kost, who headed the research, said in a press release.
Kost and his team created synthetically generated amino acid-producing bacterial mutants that released an increasing amount of amino acids into their environment. After placing them on a two-dimensional surface, they monitored the behavior of both cooperative and non-cooperative bacteria.
"The importance of this mechanism is due to the fact that no complicated or newly-evolved condition, such as the recognition of potential cooperation partners, needs to be fulfilled to effectively stabilize this long-term partnership," he said. "Two cooperating bacterial strains and a two-dimensional surface are sufficient for this protective effect to occur."
The next step for the researchers is to examine the extent of this synergistic cooperation - for example, does it occur when more than two bacterial species are involved? In addition, whether this sort of behavior evolves in natural habitats, such as soil, remains to be verified.
