After the discovery of the lux operon, the use of bioluminescent bacteria as a laboratory tool is claimed to have revolutionized the area of environmental microbiology. The applications of bioluminescent bacteria include biosensors for detection of contaminants, measurement of pollutant toxicity  and monitoring of genetically engineered bacteria released into the environment. Biosensors, created by placing a lux gene construct under the control of an inducible promoter, can be used to determine the concentration of specific pollutants. Biosensors are also able to distinguish between pollutants that are bioavailable and those that are inert and unavailable. For example, Pseudomonas fluorescens has been genetically engineered to be capable of degrading salicylate and naphthalene, and is used as a biosensor to assess the bioavailability of salicylate and naphthalene. Biosensors can also be used as an indicator of cellular metabolic activity and to detect the presence of pathogens.