Quorum Sensing: What We Can Learn From Eavesdropping on Bacteria
The sun has long disappeared over the horizon, but a deep glow emits from inside the ocean. The shimmering water takes on an unnerving shade of electric blue. To many mariners over the past centuries, this rare occurrence was proof that the ocean had fantastic creatures hidden in its depths that we had yet to explore and understand. And they weren’t entirely incorrect.
This phenomenon, known as the milky seas, is due to the bioluminescence of the bacteria Vibrio fischeri. In 1970, the scientists Kenneth H. Nealson and John W. Hastings of Harvard University were running tests on these vibrant Vibrio fischeri bacteria when they noticed something rather strange. A lone bacteria, in dilute suspension, would not emit any light. However, when allowed to grow to a certain cell population size, they would all light up, as if someone had flipped the switch on a string of Christmas lights.
It’s as if the simple bacteria are able to coordinate and act in perfect synchronicity with each other! How can this be? Welcome to the world of quorum sensing. Essentially, quorum sensing is the system that bacteria use to communicate with one another and regulate their gene expression based on population density.
To understand why bacteria use quorum sensing, imagine this: A single bacteria invading a host body doesn’t stand a good chance of succeeding because the immune system can easily stop a low-volume attack. So, it’s in that bacteria’s best interest to wait quietly until it knows that there are enough bacteria accompanying it. Then, they can virulently infect the host cell all at once. Sneaky, but effective. How do they do it?
Essentially, like humans, bacteria have their own languages. They communicate using chemical signals known as autoinducers. Autoinducers are secreted by the bacteria, and once the autoinducers are present at a high enough concentration, they can activate the transcription of certain genes, such as luminescence. In fact, according to research done by Stephan Schauder and Bonnie L. Bassler, each bacteria type uses a slightly different autoinducer so that the messages don’t get mixed up. However, they also found that there is a common five-carbon molecule that is produced by every single bacterium. Dr. Bassler dubs it the “bacterial Esperanto” because it is used to communicate among different species of bacterium!
The bacterial Esperanto and common bacterial sensors may be the future of combating viruses, especially as bacteria begin to develop antibiotic immunity. As Andrew Pollack writes in his New York Times article, “Drug Makers Listen in While Bacteria Talk,” researchers are working to design molecules that will clog up bacterial sensors. Like putting on noise-canceling headphones, these molecules would muffle the impact of the signaling molecules, limiting the ability for virulent bacteria to communicate.
Quorum sensing is a fascinating framework that can help explain glowing oceans and nasty colds, as well as having promising implications in fighting infections and antibiotic immunity. The bacteria are talking. All we have to do is listen.
González, Juan E., and Neela D. Keshavan. “Messing With Bacterial Quorum Sensing.” American Society for Microbiology: Microbiology and Molecular Biology Reviews, Dec. 2006.
Miller, Steven D., Steven H. D. Haddock, Christopher D. Elvidge and Thomas F. Lee. “Detection of a Bioluminescent Milky Sea From Space.” Proceedings of the National Academy of Sciences of the United States of America, 4 Oct. 2005.
Pollack, Andrew. “Custom-Made Microbes, at Your Service.” The New York Times, 17 Jan. 2006.
Pollack, Andrew. “Drug Makers Listen In While Bacteria Talk.” The New York Times, 27 Feb. 2001.
Rutherford, Steven T., and Bonnie L. Bassler. “Bacterial Quorum Sensing: Its Role in Virulence and Possibilities for Its Control.” Cold Spring Harbor Perspectives in Medicine, Nov. 2012.
Schauder, Stephan, and Bonnie L. Bassler. “The Languages of Bacteria.” Genes and Development, 2001.