The new bacteria can withstand high concentrations of mercury

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[SANTIAGO] Using genetically modified (GM) bacteria may be a cheaper and easier way to clean up waterways contaminated with one of the most toxic heavy metals, mercury, according to a study.

Mercury emissions are rising globally, largely from coal-fired power stations, waste incinerators, and the mining of gold and silver in developing countries — where millions are affected directly through mining or contaminated food. Exposure to the most toxic form, methyl mercury, found in seafood, can result in permanent brain damage. The UN is working on setting up a legally binding instrument on mercury emissions.

Biological clean-up methods, such as bacterial leaching, are commonly used for less toxic metals such as copper, but they do not work for mercury because there are no naturally occurring bacteria that accumulate mercury.

Now, researchers from the Inter American University of Puerto Rico, United States, have developed two GM bacteria containing genes that withstand very high concentrations of mercury. Their work was published online in BMC Biotechnology this month (12 August).

"Our bacteria are not only very resistant to mercury but also accumulate mercury to high concentrations within the bacterial cell. Unlike other transgenic bacteria, ours do not release mercury into the environment," lead researcher Oscar Ruiz told SciDev.Net.

The more efficient of the two — which carries a mouse gene for a protein called metallothionein — survived in a liquid solution containing 24 times more mercury than the amount that would kill non-resistant bacteria. In five days these bacteria mopped up 80 per cent of the mercury in the solution.

The protein is a natural 'heavy-metal scavenger', helping the bacterial cells accumulate mercury and protect themselves from its effects. The bacteria form clumps that can be easily removed from the solution.

The accumulated metal can then be recovered and recycled for industrial application, said the researchers.

According to Ruiz, their method would be cheaper and easier to use than existing processes, which rely on removing and transporting large bodies of polluted water to chemical treatment facilities, which is environmentally disruptive because the water might not be returned to the site.

"The approach we envision consists of pumping the water in situ into columns containing the engineered bacteria. The clean water can then be returned to the site," he said, adding that they are looking for investors to develop a commercial product.

José Guerrero, an expert on the use of biological clean up in mining and a professor at the César Vallejo University, Peru, told SciDev.Net that the research is novel and interesting but added that the procedure needs to be assessed on site.

"Mercury-polluted bodies of water, for which the process is intended, are very scattered so they may require the construction of reservoirs of contaminated water in order to treat it," he said, adding that this may make the process expensive and difficult to implement.

Another issue is the approval required for the release of genetically engineered bacteria into the environment, as most countries — except those in the European Union and the United States — only have regulations for introducing GM plants.

Link to full paper in BMC Biotechnology