SCI-TECH & AGRI

Fungi that live off radiation at Chernobyl



It was shown how ionising radiation encourages growth of melanised fungi

Like chlorophyll, melanin uses a part of the electromagnetic spectrum to benefit the fungiThe 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@yahoo.co.uk

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