Scientists have found that bacterial quorum sensing controls when and which cells in a given population will release “public goods” into their environment, and does so in a way that is at least partly achieved by specific metabolic advantage “incentives” for the individual cells.

Quorum sensing (the form of intercellular bacterial communication that enables individual cells to recognize and react to the cell population density of their surrounding community) is a key regulator of the production and release of “public goods” - extracellular products that can be used by any community member. The quorum sensing system is also involved in controlling expression of a few “private goods” - intracellular products not available to other cells. In this study published in the October 12, 2012, issue of the journal Science, the opportunistic lung pathogen Pseudomonas aeruginosa was studied under various metabolic conditions that changed the metabolic cost/benefit balance of producing “public goods” and thereby the competitive balance between “cooperator” cells and “cheater” cells; “cheater” cells being quorum sensing mutants that no longer produce “public goods” in response to increasing population density.

The scientists, from the University of Washington School of Medicine (Seattle, WA), found that quorum sensing–controlled expression of certain intracellular “private goods” can put a metabolic constraint on “cheater” cells and prevent a population collapse. When the researchers manipulated the environment so that the cost of cell cooperation was high and so induced destabilization of cooperation, the “cheater” cells were found to overtake the cooperating producer cells until the population collapsed. The scientists were also able to manipulate environmental conditions to restrict the “cheater” population growth and stabilize quorum sensing (population density) dependent cooperation, thereby providing the “public goods” required to maintain the population and prevent collapse of the community.

Metabolic constraint of social “cheating” provides an explanation for “private goods” regulation by a cooperative system and has general implications for population biology, infection control, and stabilization of quorum-sensing circuits in synthetic biology. The findings also provide additional indication of the potential for developing antibiotic-independent approaches to manage infections. In the future, conditions may be manipulated in order to cause cell populations of dangerous pathogens to collapse - "Perhaps, one day, we'll be able to manipulate infections so that bacterial cooperation is destabilized and infections are resolved," said Dr. Peter Greenberg, UW professor of microbiology and principal author of the study. "We've also gained new insights into how cell cooperation can be stably maintained in biology. It is much more straightforward to study sociality in bacteria than in animals. The payoffs may be in understanding what drives cooperation and conflict in general, and in developing strategies for infection control,” added Prof. Greenberg.

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University of Washington School of Medicine