Bioremediation research is a complex undertaking, which requires in-depth understanding of all interacting factors. Most of the information on the biodegradation of toxic chemicals has come from studies using pure cultures grown at high substrate concentrations in laboratory media under controlled conditions. However, in nature microorganisms are exposed to different conditions. They may be exposed to insufficient supply of inorganic nutrients, different temperatures, and pH values that may result in their loss of viability. They may be benefited or harmed by the presence of alternate substrates and by the activities of other microorganisms that are present in the environment. Thus, results obtained by pure culture studies have their limitations and cannot always be extrapolated to nature. It is therefore extremely important to have not only in vitro information on biodegradation but also understanding of environmental stresses microorganisms are exposed to in nature. Hence, to increase the likelihood of a microorganism's bringing about a reaction in nature that it can perform in axenic culture in laboratory media, the identities of abiotic and biotic stresses and the means to overcome them must be established. The information can then be used to construct a genetically engineered microbial strain that is not only capable of degrading toxic chemicals at a faster rate but is also able to withstand environmental stresses when introduced back into the environment.
There are several reasons for the failure of microorganisms to enhance biodegradation when inoculated back into the environment. Even microorganisms that are successful in one environment may not be successful in another environment. These reasons for failure often reflect ecological constraints on the introduced organism. Some of the ecological constraints responsible for the failure of inoculation to enhance biodegradation have been mentioned under biodegradability. Briefly, they are: (1) alternate substrate, (2) presence of toxins in environment, (3) bioavailability of the substrate, (4) temperature, (5) predation, and most importantly (6) competition from ecologically established microbial flora in the environment.
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