Colonies of luminescent bacteria promise to become biological sensors capable of detecting a variety of parameters such as temperature, pressure or specific chemicals. The microbes, engineered at Britain's chemical and biological defense laboratory, glow when they are exposed to changes in pressure, and researchers there hope to make other bacteria that respond to different environmental factors. The bacteria have several types of protein on their cell walls that are sensitive to changes in the environment. When these proteins detect environmental change, they activate genes within the bacteria that, in turn, modify the bacterium's cell wall and its outer membrane so that it survives the environmental change. Researchers led by Rick Titball, the head of microbiology at the laboratory, chose a protein that responds to pressure. Using genetic engineering techniques, they linked the protein's respective gene to a gene that creates luciferase, a substance similar to what gives fireflies their glow. Now, when the bacteria encounter changes in pressure, they create luciferase and glow. Titball said that the researchers are looking to test the limits of the bacteria's response. He said that once the group finds the limits they can begin to look at applications, because they will have the "underpinning technology." The microbes themselves are robust enough to be good sensors. "There are all sorts of applications outside of the field of detecting toxic chemicals. Youmight use [the technique] to monitor the exposure of foodstuff to extremes of temperature,"he added.