Recombinant Bacterial Reporter Systems

Unlike traditional biosensors, based on the unique specificity endowed by the intrinsic characteristics of biological recognition elements, the greatest advantage of whole-cell biosensors is in the global nature of their responses. To assay the potential biological effects of a sample on a live system, one needs a live system as a part of the testing protocol. There are many good reasons to avoid the use of live animals for this purpose, and one of the most promising alternatives is the use of natural or genetically engineered microorganisms that respond to predetermined types of biological effects or classes of chemicals. While some of the specificity characterizing molecule-based biosensors may be lost, it is more than compensated for by the fact that by using live cells we are able to detect, by very simple means, very complex series of reactions that can exist only in an intact, functioning cell. Only a sensor of this type can report on the “well-being” of a system, on the toxicity of a sample, the genotoxicity of a chemical, or the bioavailability of a pollutant. No molecular recognition or chemical analysis can provide this type of information. Genetically engineered whole-cell biosensors are usually constructed from a recognition/sensing element that drives a reporting element within a live host cell. To constitute a biosensor, such cells need to be incorporated into a solid platform and coupled into a signal transduction apparatus that will detect, amplify, and translate the biological signal emitted in response to the target conditions. The potential options for selecting and combining these four building blocks—sensor, reporter, cell, and hardware—are numerous. Some of these combinations are described in this chapter.