The cell surfaces of many microbes latch onto heavy metals, but this metal 'sequestering' is too feeble to significantly reduce metal pollution in soil. Although the toxic metal remains in the soil, once bound to the modified bacteria it is less likely to be taken up by plants and animals. The problems of heavy metal pollution are well known in Spain. In April 1998, about five million cubic metres of polluted water spilled from a mine residue pool near Seville, ruining crops and leaving surrounding farmland useless. Although the floodwater was successfully diverted away from a nearby national park, the ecological effects are expected to linger for years, as the zinc, lead and other metals left in local groundwater work their way through the food chain.
Microorganisms offer a cheap way to clean up pollution.
Bugs that convert toxic substances, including oils and solvents, to harmless gas are becoming increasingly popular, not least because they are robust, easy to manage and don't stop working to read the newspaper. But 'treating' metal pollution does not necessarily mean removing it from soil, de Lorenzo's team shows. They can make cadmium in soil less harmful by attaching it to the bacteria Ralstonia eutropha , a strain naturally resistant to heavy metal pollution. These genetically modified bacteria escape many of the strict conditions governing other GM experiments. The researchers also give the soil bacteria part of another gene that encourages the cadmium-luring proteins to sit on the bacterial outer membrane, so that they are fully accesible to the pollutant.