if two types of bacteria that cannot naturally live together are forced to do so, they can rapidly clean up sites contaminated with toxic metals. Geoffrey Gadd and colleagues at the uk's Dundee University claim to have designed a system that allows two types of soil bacteria to work in tandem to remove metals efficiently.

The system consists of a reactor split into two compartments. One compartment holds bacteria that depend on air. It oxidises sulphur and dissolves heavy metals ores.

The other compartment contains bacteria that can only survive in the absence of oxygen, thereby reducing sulphur and metal content. Contaminated soil is pumped continuously through both compartments, allowing each type of bacteria to independently clean the earth, according to the researchers.