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researchers at University of Delhi's South Campus have developed a new technique that uses microbes to detect toxic metals and metallic compounds in industrial effluents.
The process uses a dead bacterium's ability to give off signature colour when certain metals or their compounds come into contact with it. The team of scientists, led by Sheela Srivastava, used dead colonies of bacterium Pseudomonas stutzeri rs34 and effluents containing compounds of copper, cobalt, manganese and zinc. They found with an effluent containing copper, the dead bacterial biomass became green and with cobalt it acquired a pink hue. Significantly, the detection is possible even when more than one metal is present in the effluent. "Using such unicellular organisms as the first detection kits can have certain advantages," Srivastava told Down To Earth.
The common, chemical-based methods to detect toxic metals are costly, require exhaustive lab analysis, and in the long run, may also prove environmentally damaging, said the scientists in their report published in Current Science (Vol 89, No 7, October 10, 2005). In comparison, the new process is not only cheap, but also quick and easy to perform, they said. But this method does not work for some highly toxic metals, such as chromium and arsenic, that do not give off any colour.
Explaining the mechanism, Srivastava said the bacterial cell wall has several negatively-charged sites, which bind to a variety of metals. In fact, they function better in a dead state, as the cells allow the metal to freely enter and bind to more sites inside the cell, too. For instance, in the case of copper, although the dead cells took up less metal in comparison to live cells, the colour of the biomass was more intense in the former case. Besides, dead bacteria is both easy to manipulate as well as safe to handle.
According to the scientists, the technique works even when the concentration of metals in the solution is as low as 2 parts per million.