August 2005

From the Lab: Biotechnology

Engineered E. coli bacteria signal environmental changes and dividing cells could mend tissue after heart attacks.

By Technology Review

Bacterial Sensors
Engineered E. coli bacteria signal environmental changes

Results: Princeton University and Caltech researchers have genetically engineered E. coli bacteria to give off red or green fluorescent light in response to different concentrations of a cell-signaling molecule secreted by a third type of E. coli. Incubating the three types of E. coli in petri dishes resulted in controllable patterns. In one experiment, the researchers produced concentric circles of different colors, with the signaling cells in the center. Surrounding them were two types of fluorescing cells: one that emitted green light when sensing a high concentration of the signaling molecule, and another that gave off red light at medium concentrations.

Why it Matters: Researchers had previously programmed cells to communicate individually or in small groups. Here the Princeton and Caltech team engineered larger populations of bacteria to work together to form visible patterns that could be used, for example, to signal the presence of a toxic chemical. Because the bacteria produce different signals in response to concentrations of a target chemical, they could flag areas of high concentration as likely sources of wider contamination. In theory, bacteria-based sensors could be more sensitive to a broader range of chemicals than conventional sensors are.

Methods: The researchers, led by Ron Weiss and Frances Arnold, used mathematical models of gene activity to predict the responses of different strains of E. coli to distinct ranges of signaling-molecule concentrations. The researchers then synthesized the strains likely to be most useful by inserting into the E. coli genome desired genes, such as those that code for fluorescent proteins. They then spread a mixture of these strains in petri dishes containing growth media and incubated them overnight. Using a fluorescence microscope, they took pictures of the plates to reveal the different colored patterns.

Next Step: To turn microorganisms into sensors, the researchers must couple their gene networks to receptors that specifically bind to target chemicals. They will also need to design the sensors so that the cells remain alive and stable even outdoors. And they will likely need to devise some kind of control switch to reset or turn off the sensors. -- By Corie Lok

Source: Basu, S., et al. 2005. A synthetic multicellular system for programmed pattern formation. Nature 434:1130-4.