Now, scientists have learned that bacteria use an analogous integrated communications system to sense, retrieve and process the chemical signals they depend on to find nutrients or flee from danger. The new finding, reported today (Jan. 3) in the journal Nature, may help scientists unravel the secrets of how cells communicate with one another, a development that could, among other things, spur new vaccine strategies or the creation of surfaces that naturally repel pathogenic microbes.
Bacteria - and other types of cells - use receptors on their surface to sense their environment and, like a human nose, pick up chemical cues from a distance, said Laura L. Kiessling, a University of Wisconsin-Madison professor of chemistry and biochemistry and the senior author of the Nature paper.
"The receptors act like a sensory organ and help the cell integrate and respond to many different signals," said Kiessling who conducted the study with UW-Madison graduate student Jason E. Gestwicki.
Scientists have long known that the membrane-spanning receptors on cells are conduits of chemical information. What they did not know, according to Kiessling, is that clusters of receptors on the cell surface act in concert to "amplify and integrate sensory information."
In their Nature paper, Kiessling and Gestwicki use a new type of signal, a synthetic multivalent attractant that can interact with several chemoreceptors, to control bacterial responses. They found that the four major types of surface chemoreceptors - each responsible for sensing particular compounds - work as a system to sense their environment and let the cell know whether to move toward or away from the source of a chemical signal.
"They have to collaborate," said Kiessling. "The whole array of receptors acts to sense a compound."
In the case of the bacterium Escherichia coli, the microbe that is the basis of the Wisconsin study, it responds differently to different chemical cues. Sensing a nutrient, they tend to swim toward the source in hopes of a meal; sensing a potentially damaging chemical they tend to tumble away from the source.
Kiessling noted that cell chemoreceptors are known to be extremely sensitive, able to detect changes in concentration as low as 5 percent.
The discovery of a collaborative mode of information exchange provides critical insight into how cells in general, not just bacterial cells, can be so highly sensitive to their environments, Kiessling said. While the Wisconsin study was conducted with E. coli bacteria, similar communication models have been proposed, but not demonstrated, for the key cells in the human immune system.
"The immune system has to respond very sensitively to foreign invaders," she said, "and if similar signal amplification is in play in humans, it will give us a better understanding of how cell receptors work together" to put the human immune system to work to fight off an infection.
Also, a new understanding of the cell communication infrastructure, Kiessling noted, could lead to general strategies to aid the never-ending battle against pathogenic microbes. For example, it might now be possible to interfere with the signaling processes that make bacteria and other microbes pathogenic, virulent and able to make biofilms.
If one could interfere with biofilm formation, it could recast the problem of antibiotic resistance as biofilms harbor antibiotic-resistant bacteria. For example, cystic fibrosis is caused by a bacterial film in the lung. Short-circuiting the bacterium's tendency to collect in a film by hindering its ability to communicate, could underpin new strategies for treating what is now an intractable disease.
The discovery that synthetic compounds can alter bacterial communication could also lead to the development of germ-resistant surfaces for homes, schools and hospitals.
The Wisconsin study was supported by a grant from the National Institutes of Health, and patents for the discovery have been applied for through the Wisconsin Alumni Research Foundation.
Terry Devitt (608) 262-8282, trdevitt@facstaff.wisc.edu
Journal
Nature