10. Biosensors
By fusing reporter genes to specific catabolic gene promoters, biosensors can be designed to switch on in the presence of a particular pollutant. This approach has been successfully employed with luxbased
(luminescent) systems. For example, Burlage et al. (1990) developed a lux-modified bacterial biosensor to identify the presence of naphthalene, and Selifonova et al. (1993) constructed biolumines cent biosensors to detect bioavailable Hg (II) in the environment. To our knowledge, there have been no published studies on the use of gfp-tagged cells as biosensors of environmental pollutants. Since there are many advantages to using the GFP for environmental studies (Table 2), our laboratory is currently developing a GFP-based biosensor for environmental pollutant detection. Bioluminescentbased biosensors have also been used to measure acute toxicity as they respond to the presence of toxic compounds with a decline in light production, reporting the effect of the toxicant on bacterial metabolic activity. Since the GFP is not dependent on metabolic activity for its fluorescence, it may not be a useful system for toxicity assessment.