Bioremediation is the concept in which biological organisms are used to repair the environment; essentially, when biology meets ecology. This is an advantageous way of eliminating radioactive/toxic waste at radioactive storage sites and facilities. Physicochemical clean-up costs of such sites can amount to as much as 265 billion dollars, making bioremediation a cost effective and environmentally intelligent way of eradicating hazardous toxic waste.
The process of nuclear waste bioremediation utilizes microorganisms such as bacteria to break down or precipitate harmful, radioactive substances. In order for this to occur, the organism being utilized must be able to withstand the potential cellular damage caused by the radioactive waste at the eradication site. Deinococcus radiodurans (D. rad) is the most radiation resistant bacteria known; D. rad is resistant to ionizing radiation, desiccation, ultraviolet radiation, oxidizing agents and electrophilic mutagens. Considering these extremophilic anomalies, D. rad is the perfect candidate for use in bacterial bioremediation efforts. It is already being tested in bioremediation efforts at sites of U.S nuclear weapon production during cold war, where a vast amount of toxic waste still remains.
There are multiple ways of accomplishing bioremediation; the substance being remediated determines the strategy used.
Toxic organic compound degradation is for the detoxification of contaminated solvents produced during nuclear weapons production. These include radioactive organic solvents such as toluene and other aromatic compounds. In recent years, D. rad strains have been produced with solvent-degrading capabilities to accomplish these goals. D. rad expressing the enzyme todC1C2BA, derived from Pseudomonas putida, have been successfully created. These D. rad strains have been used to oxidize toluene, which is then metabolized and eventually forms insoluble polymers. These insoluble polymers precipitate out of and can then be easily removed from the waste solution.
Heavy metal remediation is used in the clean up of radioactive metals such as mercury, chromium and uranium. One way to achieve heavy metal remediation is to insert an enzyme into D. rad, giving D. rad the ability to reduce and diminish the toxicity of a particular metal. (merA), which coverts mercury to a less volatile and dangerous oxidation state, has been expressed in D. rad and used in such applications. PhoN, a nonspecific acid phospatase, has also been expressed in D. rad and has been used to precipitate radioactive uranium at nuclear weapon production sites1.
Recognizing D. rad as the greatest terrestrial organism for resistance to environmental stressors, our NYC iGEM team is looking to identify and add to the knowledge of key stress-resistance genes in D. rad. Ultimately, our goal is to create a bacteria with the capacity to withstand the harsh environment of Mars, enabling terraforming in order to sustain future human colonization.
1. Appukuttan, D., Rao, A.S., Apte, S.K., Engineering of Deinococcus radiodurans R1 for Bioprecipitation of Uranium from Dilute Nuclear Waste, 2006. 72(12): 7873–7878.
2. Brim, H., McFarlan, S.C., Fredrickson, J.K., Minton, K.W., Khai, M., Wackett, L.P., Daly M.J., Engineering Deinococcus radiodurans for metal remediation in radioactive mixed waste environments, 1999. 18: 85-90. ,
3. Daly, M.J., Engineering radiation-resistant bacteria for environmental biotechnology, 200. 11(3): 280-5.