A population of bacteria has a metabolic tactic for keeping its rogue members in check, researchers report (Science, DOI: 10.1126/science.1227289). The discovery could someday be useful for controlling infections or for making industrial fermentations more efficient. Pseudomonas aeruginosa activates certain genes upon reaching a threshold population by using a communication system called quorum sensing. One of those genes prompts secretion of an enzyme that digests an extracellular protein source. Some individual microbes, however, don’t heed the quorum-sensing call and live off the protein digested by nearby bacteria. Ajai A. Dandekar, Sudha Chugani, and E. Peter Greenberg of the University of Washington School of Medicine have now found a way to restrain freeloaders so they don’t sabotage the population. The cheaters, as Greenberg calls them, don’t turn on a gene to produce an intracellular enzyme that metabolizes adenosine. They can thus be held in check by adding a small amount of adenosine to the medium where they grow. Engineering similar pairs of quorum-sensing-controlled genes could be the key to controlling cheaters in microbes used to secrete enzymes or small molecules on industrial scales, Greenberg notes. “We can manipulate the situation so that cheaters never prosper,” he says.