bioreporters are intact, living microbial cells that have been genetically engineered to produce a measurable signal in response to a specific chemical or physical agent in their environment. bioreporters contain two essential genetic elements, a promoter gene and a reporter gene. the promoter gene is turned on (transcribed) when the target agent is present in the cell’s environment. the promoter gene in a normal bacterial cell is linked to other genes that are then likewise transcribed and then translated into proteins that help the cell in either combating or adapting to the agent to which it has been exposed. in the case of a bioreporter, these genes, or portions thereof, have been removed and replaced with a reporter gene. consequently, turning on the promoter gene now causes the reporter gene to be turned on. activation of the reporter gene leads to production of reporter proteins that ultimately generate some type of a detectable signal. therefore, the presence of a signal indicates that the bioreporter has sensed a particular target agent in its environment.