One of the most successful projects of large-scale biore-mediation was undertaken at the beaches of Prince William Sound, Alaska. Enhanced degradation of oil by application of inorganic nutrients (slow-release fertilizers) and inoculation of microorganisms capable of degrading oil convinced government officials that biore-mediation was a viable alternative for at least some hazardous waste problems. Fertilizer applications stimulated the indigenous microorganisms to degrade the oil contaminating the beaches at faster rates.
Molecular biology provides highly useful techniques to modify microorganisms so that they have the desired properties. The process may involve separation of DNA from the cell, its treatment with specific restriction endo-nuclease to cleave the DNA, the rejoining of the DNA fragments with DNA ligase to give a new sequence of nucleotide bases, and the reintroduction of this hybrid molecule into a suitable bacterial cell in which it is replicated and expressed. These genetic modifications provide considerable promise to affect bioremediation of even the most recalcitrant compounds. Genetically engineered microorganisms introduced into natural environments face the same stresses as those affecting the existing organisms.
Some ofthe hazardous chemicals present in a contaminated site are degraded slowly, limiting bioremediation of sites contaminated with these chemicals. For example, microorganisms degrade some PCBs and PAHs very slowly, thus limiting the use of these bacteria in bioreme-diation of the sites contaminated with these chemicals. Genetically engineered microorganisms that can degrade these compounds at a faster rate can be of much value. Isolation of bacteria that are resistant to high concentrations of toxic chemicals and the use of them as hosts in genetic engineering experiments would provide an opportunity for on-site bioremediation even when the sites are highly contaminated.
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