Background Essay: Talking Bacteria

Bacteria are relatively primitive one-celled organisms called prokaryotes. Prokaryotic cells lack the nucleus and organelles of more sophisticated eukaryotic cells, which are found in plants and animals. Although bacteria cluster to form colonies, each cell can live independently of the others—unlike multi-celled organisms, whose highly specialized cells cannot survive on their own.

Until recently, scientists thought that a bacterial colony conferred no specific survival advantage to its individual members. However, recent research suggests something quite to the contrary. Through a process called quorum sensing, bacterial cells appear to communicate in a way that enables a kind of strategic coordination more commonly ascribed to social animals such as ants and humans. This cell-to-cell communication occurs not through language but through the release of chemical-signaling molecules called autoinducers. When bacteria release autoinducers into an environment and their signal is received by other quorum-sensing bacteria, the group can exhibit a genetically programmed behavior.

Bioluminescence is one such behavior. In the natural world, luminescent bacteria called Vibrio fischeri inhabit Pacific bobtail squid. Because moonlight casts visible shadows on the sand floor, these squid are vulnerable to predators. The squid and the bacteria, in a symbiotic relationship, compensate for this by glowing to match the moonlit water in color and intensity; the quorum-sensing bacteria produce this glow from inside their host. With their host protected, the bacteria are protected as well. While an individual bacterium can do little on its own to produce change around it, a group of coordinated cells can produce behaviors that afford a colony an evolutionary advantage.

New research suggests that quorum sensing occurs among many bacterial species. In fact, it might be the mechanism that enables pathogenic, or disease-causing, species to multiply, concentrate, and overpower a body's immune system, thereby establishing infection in a host. Although antibiotics exist to combat many infections, some bacterial strains have developed a resistance to the treatments through repeated exposure.

In the face of rising resistance to existing drugs, pharmaceutical researchers are looking for ways to use their understanding of quorum sensing to control disease. One approach is to disrupt cell-to-cell communications by blocking the receptors that bacteria use to receive the molecular signals. If researchers can find a way to prevent bacteria from communicating, they may be able to effectively combat diseases caused by antibiotic-resistant bacteria.