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RED HERRING | Bacteria Talk and Manipulate
Wednesday, October 12, 2005
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Bacteria Talk and Manipulate
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Scientists learn bacteria species communicate, and adjust their conversations to block or
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Entertainment & Media spread human infection.
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September 30, 2005
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Bacteria may be single-cell creatures, but they’re far from dumb: They not only can talk to each other, but some
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species can also manipulate other species’ behavior to block or spread infection in humans.
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That’s the latest discovery from a group of Princeton University molecular biologists whose findings on the
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science of bacterial communication appear in the current issue of the journal Nature. The results could have
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important implications for designing better antibiotics.
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Bacteria talk to each other by secreting chemical signals called pheromones, or autoinducers, into the
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environment, where they can be sensed by other bacteria cells. When this happens, it changes the behavior of
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the cells that pick up the signal by turning on and off combinations of their genes.
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The trick is called quorum sensing. It allows bacteria to coordinate the behavior of whole colonies, giving them
some of the characteristics of multicellular organisms.
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When the chemical signal induces another
bacterium to produce the same chemical, it can
be used to sense the population density.
For example, a species called Pseudomonas
aeruginosa, which can cause devastating
infections in cancer and AIDS patients, can
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increase in number without harming its host.
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-6.97 However, quorum sensing allows the bacteria
Delayed 20 mins. to monitor their population density. When they
hit a threshold great enough to overcome the
immune system, the bacteria cells change to
become aggressive.
“Quorum sensing-controlled processes are often crucial for successful bacterial–host relationships—both
symbiotic and pathogenic,” said the paper.
Manipulating the Signal
Most autoinducers are produced to communicate with bacteria of the same species. However, one autoinducer,
known as AI-2, is produced and detected by many different species. For this reason it is widely believed to
facilitate communication between species.
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RED HERRING | Bacteria Talk and Manipulate
In the study, Karina Xavier, a postdoctoral fellow at Princeton University’s Howard Hughes Medical Institute,
demonstrated this theory by mixing a common gut bacteria called Escherichia coli with a bioluminescent marine
bacteria called Vibrio harveyi, which uses quorum sensing to coordinate bacteria cells to glow when they hit a
threshold density.
Her findings confirmed that both species responded to AI-2 produced by another species.
Another experiment showed that E. coli could take advantage of the common language to confuse the marine
species. It ate up enough AI-2 to dim the glow of the marine species, fooling it into thinking its population
numbers had dropped.
Finally, Dr. Xavier mixed E. coli with the bacterial species that causes cholera and would naturally mix with it in a
human gut.
The cholera-producing species, called Vibrio cholerae, uses quorum sensing to tell when its population has
increased sufficiently to make it worth moving on to infect another human.
When the population reaches this threshold, the chemical signal tells V. cholerae to detach from the intestine
walls and stop producing toxins. Again, E. coli managed to block the V. cholerae signal.
“Consumption of the signal could be a mechanism that allows one kind of bacteria to block another kind of
bacteria from counting how many neighbors they have and, in turn, properly controlling its behavior,” said
Bonnie L. Bassler, a professor of molecular biology at Princeton.
“You can imagine that, in niche one, the bacteria we consider good guys might be using AI-2 and winning. And
unfortunately, in niche two, the bad guys might be using AI-2 and winning,” she added.
And this could add another layer of complexity to antibiotic prescription and design.
The Princeton team is currently trying to develop molecules that interfere with a bacterium’s ability to detect and
produce AI-2.
“A more far-out strategy is to develop therapies that enhance the growth of AI-2 consumers at the expense of
bacteria that rely on AI-2 for counting to turn on virulence,” Professor Bassler told RedHerring.com, adding that
this strategy is still some way off. “We try to manipulate the manipulators!”
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