Engineered bacteria scavenge heavy metals and then hold them for recycling

By Roger Segelken

Biotechnologists at Cornell have engineered a strain of bacteria with two environment-saving abilities: to soak up heavy-metal pollutants, such as mercury, and then to sequester them for recycling.

Now the researchers are ready to begin field trials of a system that should reduce water and soil contamination to the parts-per-trillion level.

This bioremediation process kills the bacteria, and that's a good thing, chemist David B. Wilson and graduate students Shaolin Chen and Zhiqui Hao reported at the American Chemical Society meeting. Wilson is professor of biochemistry, molecular and cell biology as well as director of the Institute for Comparative and Environmental Toxicology.

Focusing first on mercury, one of the most toxic heavy metals in the environment, the researchers engineered Escherichia coli (E. coli) bacteria both with genes from another bacterium -- to seek and transport mercury through E. coli cell membranes -- as well as genes from yeast -- to accumulate mercury inside each E. coli cell. The same strategy, they believe, can be used to re-engineer E. coli specifically to scavenge metals such as cadmium, zinc, nickel or manganese.

To date, the process has been tested successfully in laboratory-scale bioreactors with hollow-fiber filters holding billions of bacterial cells while water-borne mercury is pumped through the bioreactor. Scaling up the process, Wilson envisions bioremediation using mobile bioreactors working at sites with water or soil contamination or with factory-based bioreactors to treat effluent from industrial processes.

The bacterial process would not be a cost-effective primary treatment for high concentrations of mercury or other pollutants, Wilson said, "but in dilute solutions we can get every last bit of mercury." That is important, he added, "because mercury, even in low concentrations, is turning out to be more toxic than we thought."

His laboratory is close to developing bioengineered bacteria to scavenge cadmium and next will work on a similar system for cleaning up nickel contamination.