With a tweak to their genetic codes, bacteria have been coaxed to follow a chemical trail of a researcher’s choosing.
Chemotactic bacteria, such as Escherichia coli, recognize and move toward certain chemicals. The chemicals bind to proteins on the microbe’s surface, inducing an internal mechanism to drive the microbe’s flagellum, a tail-like structure.
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Chemists Justin P. Gallivan and Shana Topp of Emory University in Atlanta wanted bacterial cells “to follow things that we want them to follow,” Gallivan says. Rather than engineering one of the bacterial-cell-surface proteins to recognize a new chemical, the researchers focused on one of the internal proteins that controls the E. coli flagellum. The microbe moves forward when this protein, called CheZ, is present, but stays in place if it’s absent.
Gallivan and Topp put the gene for CheZ under the control of a riboswitch—a stretch of RNA that binds to specific molecules—that’s sensitive to the chemical theophylline. Only when this chemical binds to the riboswitch does the production of CheZ proceed.
The researchers painted paths of several chemicals on a cell-culture plate. They then grew on that plate E. coli carrying the theophylline-sensitive riboswitch. The cells moved along only that chemical’s path, Gallivan and Topp report in the May 30 Journal of the American Chemical Society.
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The researchers are now developing riboswitches for particular applications, Gallivan says. For example, some bacteria can degrade pollutants. Engineered to follow a pollutant’s path, the microbes might be used to clean up an environmental waste site, he notes.