Until recently, the ability of bacteria to communicate with one another was considered an anomaly that occurred only among a few marine bacteria. It is now clear that group talk is the norm in the bacterial world, and understanding this process is important for fighting deadly strains of bacteria and for understanding communication between cells in the human body.
Bonnie Bassler has discovered that bacteria communicate with a chemical language. This process, called quorum sensing, allows bacteria to count their numbers, determine when they have reached a critical mass, and then change their behavior in unison to carry out processes that require many cells acting together to be effective.
For example, one process commonly controlled by quorum sensing is virulence. Virulent bacteria do not want to begin secreting toxins too soon, or the host's immune system will quickly eliminate the nascent infection. Instead, Bassler explained, using quorum sensing, the bacteria count themselves and when they reach a sufficiently high number, they all launch their attack simultaneously. This way, the bacteria are more likely to overpower the immune system. Quorum sensing, Bassler says, allows bacteria to act like enormous multicellular organisms. She has shown that this same basic mechanism of communication exists in some of the world's most virulent microbes, including those responsible for cholera and plague.
Working with Vibrio harveyi, a harmless marine bacterium that glows in the dark, Bassler and her colleagues discovered that this bacterium communicates with multiple chemical signaling molecules called autoinducers (AIs). Some of these molecules allow V. harveyi to talk to its own kind, while one molecule—called AI-2—allows the bacterium to talk to other bacterial species in its vicinity. Bassler showed that a gene called luxS is required for production of AI-2, and that hundreds of species of bacteria have this gene and use AI-2 to communicate. This work suggests that bacteria have a universal chemical language, a type of "bacterial Esperanto" that they use to talk between species.
Bassler's research opens up the possibility for new strategies for combating important world health problems. Her team is currently working to find ways to disrupt the LuxS/AI-2 discourse so the bacteria either cannot talk or cannot listen to one another. Such strategies have potential use as new antimicrobial therapies.
Her interest in bacterial communication grew from her curiosity about how information flows among cells in the human body, and she is convinced she will find parallels between the bacterial systems and those in higher organisms. "We have a chance to learn something fundamental in bacteria about chemical communication," Bassler said. "If we can understand the rules or paradigms governing the process in bacteria, what we learn could hold true in higher organisms."
Bassler won a 2002 MacArthur Fellowship, which she said provided tremendous validation for her group's research, recognizing that they are working on a problem that is much larger than a glow-in-the-dark bacterium. She was also chosen as the 2004 Inventor of the Year by the New York Intellectual Property Law Association for her idea that interfering with the AI-2 language could form the basis of a new type of broad-spectrum antibiotic. "The fantasy is to make one pill that works against all kinds of bacteria," she said.