Bioremediation is basically a technique in which micro-organisms are utilized for the management of biological waste. Their metabolism is utilized for the removal of pollutants from the environment. Bioremediation can occur on its own which is natural attenuation or can occur artificially by addition of chemicals spurred on the microbes which is termed as biostimulation. Although not all the heavy contaminants can be removed by usual bioremediation processes. In this way, bioremediation is helping man-kind and society to deal with toxic and hazardous waste which can be otherwise harmful to health and surroundings, if not removed.
Genetic Engineering has now become integrated with bioremediation since many microbes can be artificially designed which can consume the toxic waste and pollutants that are not usually taken in by normal microbes. This is done by first genetically altering the sequences of the desired microbe and enhancing its ability to digest the toxic particles of the pollutant or by genetically engineering a new microbe which has extraordinary ability to take in, consume and digest the pollutants. Thus, micro-organisms are designed specifically for bioremediation. A recent advancement in this section is the genetically modified bacterium Deionococcus radiodurans that is the most radio-resistant organism ever known. Deionococcus radiodurans can consume high amounts of radio-active ionic mercury and toluene from radioactive waste.
Published in nature biotechnology journal in the year 2000, the work of Brim H et al. reveals how this bacterium can be utilised for the given purpose. They claim to have developed a radiation resistant bacterium by genetic-modification for the treatment of mixed radioactive wastes that contains ionic mercury. The high cost of remediating radioactive waste sites from nuclear weapons production has induced the need for the development of bioremediation strategies using Deinococcus radiodurans that as mentioned before is the most radiation resistant organism ever known. As a frequent constituent of these sites is the highly toxic ionic mercury (Hg) (II), they first generated several D. radiodurans strains which were expressing the cloned Hg (II) resistance gene (merA) from Escherichia coli strain BL308. Then four expression vectors were designed for this purpose. The relative advantages of each were compared significantly and the results showed that the strains grew in the presence of both radiation and ionic mercury at concentrations well above those found in radioactive waste sites which would be significantly useful to effectively reduce Hg (II) to the less toxic volatile elemental mercury. Further, they conducted another experiment in which they showed that different gene clusters could be employed in order to engineer D. radiodurans for treatment of mixed radioactive wastes which can be done by developing a strain to detoxify both mercury and toluene. In future studies, these expression systems could be able to provide models to guide D. radiodurans engineering efforts which are expected to be aimed at integrating several remediation functions into a single host.
As recorded of the year of 2000, Seventy million cubic meters of ground and three trillion litres of groundwater had been contaminated by constantly leaking radioactive waste generated in minute quantities in the United States during the Cold War. A cleanup technology or to be clearer bioremediation technique is being developed which is based on the radiation-resistant bacterium Deinococcus radiodurans, which has been successfully engineered to express bioremediation functions.
Although there is more to the radio-resistant quality of the bacterium D. radiodurans, the question arises why D. radiodurans is so resistant to ionizing radiations. In a later study, experiments were conducted in order to expose the hiding factors. In the experiment, exponential-phase cultures of Deinococcus radiodurans were exposed to a 5000-Gray dose of gamma radiation that led to individual cells suffering massive DNA damage. Despite this insult to their genetic integrity, those cells had survived without any notable loss of viability or evidence of mutation and then repairing the damage by as-not-so-well-understood mechanisms.
The genome of the bacterium is notable too. It has been found that the bacterium Deinococcus radiodurans shows remarkable resistance to a quite specific range of damage caused by ionizing radiation and other processes like desiccation, UV radiation, oxidizing agents, and electrophilic mutagens. The bacterium is best known for its extreme resistance to ionizing radiation. Also it happens to come into notice that not only can it grow continuously in the presence of chronic radiation (6 kilorads/h), but also it can thrive into acute exposures to gamma radiation exceeding 1,500 kilorads without either dying or undergoing induced mutation. Although it is known that these multiple resistance phenotypes arise from efficient DNA repair processes, the exact mechanisms underlying these extraordinary repair capabilities remain not well understood.
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