The expectations raised in the mid-1980s on the potential of genetic engineering for in situ remediation of environmental pollution have not been entirely fulfilled. Yet, we have learned a good deal about the expression of catabolic pathways by bacteria in their natural habitats, and how environmental conditions dictate the expression of desired catalytic activities. The many different choices between nutrients and responses to stresses form a network of transcriptional switches which, given the redundance and robustness of the regulatory circuits involved, can be neither unraveled through standard genetic analysis nor artificially programmed in a simple manner. Available data suggest that population dynamics and physiological control of catabolic gene expression prevail over any artificial attempt to engineer an optimal performance of the wanted catalytic activities. In this review, several valuable spin-offs of past research into genetically modified organisms with environmental applications are discussed, along with the impact of Systems Biology and Synthetic Biology in the future of environmental biotechnology. [Int Microbiol 2005; 8(3):213-222
