Engineered bacteria to mop up mercury
By María Elena Hurtado
SciDev.net
Genetically modified bacteria may be a cheap and easy way to clean up waterways contaminated with one of the most toxic heavy metals, mercury.
Mercury polluted water
Mercury polluted water near a gold mine in southern France. Credit: AFP/Jean-Pierre Muller
SANTIAGO: Genetically modified bacteria may be a cheap and easy way to clean up waterways contaminated with one of the most toxic heavy metals, mercury.
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, which is found in seafood, can result in permanent brain damage.
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 have developed two genetically modified (GM) bacteria containing genes that withstand very high concentrations of mercury.
“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,” said lead researcher Oscar Ruiz from the Inter American University of Puerto Rico in the U.S.
A ‘heavy-metal scavenger’
The more efficient of the two bacteria – 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% 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, who published their findings in the current issue of Biotechnology.
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.
Introducing GM bacteria
José Guerrero, an expert on the use of biological clean-up in mining from the César Vallejo University in Peru, said 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 U.S. – only have regulations for introducing GM plants.