Fungus catches radioactive fallout

Edible mushrooms can mop up radioactive pollution because one of their pigments captures elements such as caesium, say chemists in France1. Radioactive caesium is a large component of waste from nuclear power stations.

The insight could lead to new ways of cleaning up contaminated soils to prevent pollutants getting into the food chain. Toxic and radioactive substances might stick to a kind of fly-paper covered in molecules like the pigments, for instance.

The research even raises hope that mushroom-inspired molecules might transport the radioactive isotope caesium-137 around the body and home in on specific tissues in radiotherapy.

Fungi such as the bay boletus accumulate caesium-137, along with other toxic metals such as lead and mercury. Caesium-137 has no known natural sources. It was part of the fallout from the Chernobyl accident in 1986.

Anne-Marie Albrecht-Gary of the Université Louis Pasteur in Strasbourg, France, and colleagues find that the binding of caesium to the mushroom pigment norbadione A is sensitive to the acidity of the fungus's environment. Caesium binds most strongly when norbadione A sheds two of its seven hydrogen atoms.

And norbadione A's caesium affinity seems to be self-perpetuating. Once a norbadione A molecule has grasped one caesium ion, its changed shape makes it accept another more readily.

A similar 'allosteric effect' occurs in the protein haemoglobin, which carries oxygen in the blood. If a haemoglobin molecule binds to one oxygen molecule, it becomes increasingly able to bind a second, then a third, and then a fourth. This makes haemoglobin very efficient at accumulating oxygen.

The French researchers also find that sodium and potassium interfere with norbadione A's ability to capture caesium. This information could be useful in manipulating the mushrooms' affinity for radioactive elements. But it presents an obstacle to using molecules such as norbadione A to deliver radiotherapy, because there is plenty of sodium and potassium in the bloodstream.

Please Register or Log in to view the hidden image!

Please Register or Log in to view the hidden image!

Please Register or Log in to view the hidden image!

References
Garaudée, S. et al. Allosteric effects in norbadione A. A clue for the accumulation process of 137Cs in mushrooms?. Chemical Communications, 2002, 944 - 945, (2002).


© Nature News Service / Macmillan Magazines Ltd 2002