All bacteria frequently live in dense communities called biofilms. They secrete enzymes that break down solid organic carbon- and nitrogen-containing molecules and feast on the components within. But not every individual bacterium will produce enzymes -- some will simply feed on what their neighbors produce. The Princeton researchers found that individual bacteria also will produce a thick coating around themselves to prevent nutrients from drifting over to the undeserving. In the thicker biofilms near the top of this microscope image, productive V. cholerae (yellow) overtook exploitive V. cholerae (red). The darker communities indicate thinner biofilms and a proliferation of bacteria that will live off the work of others.