Fungi that live off radiation at Chernobyl

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Fungi that live off radiation at Chernobyl

Hindu - Chennai,India*

http://www.hindu.com/seta/2007/09/20/stories/2007092050021700.htm

It was shown how ionising radiation encourages growth of melanised

fungi

Like chlorophyll, melanin uses a part of the electromagnetic

spectrum to benefit the fungi

The phenomenon may be useful to astronauts, who may harvest the

fungi as a food source

Occasionally, the lowliest of the lowly beings get global attention

by being at the most unexpected places.

This was what happened to some microorganisms including Cladosporium

sphaerospermum (CS). This tongue-twisting name belongs to a type of

humble fungus.

Five years ago, Dr. Arturo Casadevall, Albert Einstein College of

Medicine, New York, U.S., read in the web that a robot sent into the

still highly radioactive damaged reactor at the Chernobyl nuclear

power station, returned with samples of black fungi, which were

growing on the reactor's walls. (PhysOrg.com, May 23, 2007).

Habits revealed

It appeared that these fungi were feeding on radiation. They can no

longer keep their radiation feasting habits away from the prying

eyes of researchers.

These fungi contain melanin, a high molecular weight pigment, the

same colouring agent in our skin.

Until now, the biological role of melanin has been a mystery

(PHYSICS.ORG, 2007). In a 13-page paper in the Public Library of

Science Journal (PLoS ONE, May 23, 2007) Dr Casadevall and other

researchers explained the physico-chemical tests and in vivo

experiments with three genetically diverse fungi and four measures

of cell growth; they demonstrated lucidly how ionising radiation

brings about changes in melanin and encourages the growth of

melanised fungi.

An elegant and simple hypothesis may explain the behaviour of

melanised fungi.

" Just as the pigment chlorophyll converts sunlight into chemical

energy that allows green plants to live and grow, our research

suggests that melanin uses a different part of the electromagnetic

spectrum to benefit the fungi containing it " , Dr Ekaterina

Dadachova, one of the co-authors of the paper, explained.

Providing energy

Dr Casadevall admitted that it is pure speculation but not outside

the realm of possibility that melanin could be providing energy to

skin cells. They grew some melanised fungi and others without the

pigment and exposed them to gamma radiation.

The dark fungi grew better when irradiated (The New Zealand Herald

May 27, 2007).

Certain types of fungi grew significantly faster when scientists

exposed them to ionising radiation levels nearly 500 times more than

the background; they gained more dry weight biomass.

People despise fungi because they assume that the main job of fungi

is to decompose matter into other chemicals!

The melanin-containing microorganisms are often the dominating

species in certain extreme environments (PLoS ONE 2007) such as the

abandoned contaminated regions at Unit 4, the stricken reactor at

Chernobyl.

Living happily

They live happily in soil contaminated with radionuclides, at high

altitudes and in hostile Arctic and Antarctic regions!

There are indications that melanins are ancient pigments that have

probably been selected as they enhance the survival of melanised

fungi in diverse environments and, perhaps incidentally in many

hosts (PLoS ONE, 2007).

Casadevall and his co-workers believe that despite the high

prevalence of melanotic microorganisms in radioactive environments,

it is unlikely that they synthesise melanin for the purposes of

protection (shielding) from ionising radiation.

They noted that in the high altitude regions inhabited by melanotic

fungi, the background radiation levels are about 500-1,000 times

higher than at sea level.

Since most fungi, whether melanised or not, can withstand 17,000

times more energy, the authors consider that there is apparently no

need for melanin to remain as a radio-protective agent.

But biological pigments play a major role in photosynthesis; they

convert light energy to chemical energy.

Properties changed

Since melanin can absorb visible and UV light of all wavelengths,

the authors suggested that exposure to ionising radiation would

change the properties of melanin and affect the growth of melanized

microorganisms.

They could convincingly demonstrate their expectations. The

capability of fungi to live off radiation and make biomass may be

useful to astronauts, who may be able to harvest the fungi as a food

source.

The fungi can produce food by using enhanced levels of ionising

radiation present in outer space.

Nature's capriciousness

Nature is very capricious in revealing its resourcefulness. Lowly

beings such as fungi can teach enterprising humanity a lesson or two

in harnessing energy while surviving in unendurable environments.

K.S. PARTHASARATHY

Former Secretary, AERB

ksparth@...