Radiation-Seeking Fungus

Saturday, July 26th, 2008

In Chernobyl, wildlife is thriving. In fact, in the old reactor, a new radiation-seeking fungus is thriving:

In 1999, a robot sent to map the inside of the reactor returned with samples of a particularly black fungi, indicating an abundance of the biological pigment melanin, which also colours your skin.

Though melanin is typically associated with ‘protective’ properties – absorbing and safely transforming different electromagnetic wavelengths, such as DNA-damaging ultraviolet light – the researchers had an inkling that a more extraordinary phenomenon was allowing the fungi to prosper; something still involving the combination of melanin and radiation, but beyond the bounds of radioactive protection.

After all, even without melanin, many fungi are intrinsically radiation-resistant.

Their hunch was bolstered by findings of melanised fungi, happily congregating in the cooling pools of functional nuclear reactors, and by studies of dark, ‘radiation-seeking’ fungi, purposefully growing towards radioactive particles in soil, particularly around Chernobyl.

The team looked to the example of photosynthesis as a model, said Casadevall. If plants can use the green pigment, chlorophyll, to absorb energy from the Sun and produce a usable form of chemical energy, they reasoned, fungi might be able to use their melanin pigment and radiation energy in a similar way. They even devised the snazzy moniker, ‘radiosynthesis’, for the process.

To test their idea, the group analysed three different types of fungi, including Cladosporium sphaerospermum, the species abundant in and around Chernobyl. Using ionising radiation from the radioactive isotope, caesium-137, they exposed the fungi to radiation doses similar to those inside the damaged reactor, and about 500 times greater than the Earth’s normal background level.

Melanin-containing fungi exposed to the radiation – even when nutrient-starved on purpose – grew significantly larger and up to 2.5 times faster than fungi without melanin and those not exposed to radiation.

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