The French have always had a penchant for fungi, but one day you may be more likely to find a cep cleaning up after a nuclear accident than being served in a souffle.
Edible mushrooms might not be an obvious choice, but French scientists believe a wild mushroom might soak up radioactive caesium-137 ions as easily as it can olive oil.
Caesium-137 was released in vast quantities by the explosion at the Chernobyl nuclear power station 16 years ago and could be a major contaminant from a terrorist "dirty bomb" (a conventional bomb carrying radioactive material).
Removing metal and radioactive contaminants from exposed land is a crucial task. Aside from the threat to the environment and the health of those living nearby, toxic metal ions can be carried into the food chain by vegetation.
One clean-up solution, known as bioremediation, involves planting species that might absorb the metals from the soil and then disposing of them safely. However, no plants thrive on soil contaminated by the alkali metal caesium. So, why not a fungus?
Anne-Marie Albrecht-Gary and her colleagues at the Louis Pasteur University and the University of Strasbourg think they have found the solution in the unlikely form of the tasty bay boletus, Xerocomus badius.
"Fungi often exhibit a remarkable ability to accumulate a large variety of elements, from the heaviest of the transition metals such as lead, to the alkali metals, including radioisotopes like caesium-137," says Albrecht-Gary in a recent issue of Chemical Communications.
But, she adds, little is known about how these fungi take up such metal ions. She and her colleagues have studied the chemistry of the two pigments that give the inside of the bay boletus cap its bright yellow colour - norbadione A and badione A.
These chemicals can act like molecular crab claws, grabbing hold of metal ions in a pincer movement known as chelation. The yellow colour of the pigments provided the team with the means to test how well each latches on to metals, such as caesium.
They exploited the pigments' strong absorption of ultraviolet wavelengths to record a spectrum of the free pigment molecules. Their spectra in the presence of caesium ions are markedly different. UV spectroscopy coupled with chemical analysis revealed that norbadione A, in particular, can bind to radioactive caesium strongly. It can actually bind two caesium ions, whereas its weaker sibling badione A only has the strength to grip one at a time.
Albrecht-Gary and her colleagues believe that norbadione gets its strength from an allosteric effect. When one caesium ion enters the claw, the molecule's chemistry changes slightly so that a second gripping position opens up to accept another caesium, working like a double claw. Badione A, on the other hand has only one possible grip.
The researchers believe that norbadione A makes the bay boletus so good at sequestering radioactive caesium ions from the soil in which it grows that it should be used to remove this hazardous metal from contaminated land.
The team has dashed hopes for its use in removing toxic metals, such as radioactive caesium-137 cadmium and nickel, from the body. Its grip on alkali metals, such as the essential minerals sodium and potassium, is too strong.
Of, course one problem remains: what to do with the radioactive fungi…one can hardly cook them in an omelet.
