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Fungi Gobble Radiation to Grow, Study Says

By Scott Norris
for National Geographic News
May 22, 2007
 
Some fungi eat radiation to fuel their growth, a new study suggests.

Three species of fungi containing the black pigment melanin—a substance also present in human skin—grew larger and faster when exposed to high levels of radiation, even when deprived of nutrients.

A similar response was not seen in fungi lacking the pigment, as well as in fungi that did not receive the radiation exposure.

Researchers at Albert Einstein College of Medicine at New York's Yeshiva University were inspired by previous observations of enhanced fungus growth inside the Chernobyl Nuclear Power Plant, after a reactor at the Ukrainian facility exploded in 1986.

(See photo gallery: "Chernobyl, 20 Years After the Disaster".)

The team performed a series of experiments to test whether the fungi could be harvesting radiation to fuel their growth, much like plants do when they capture solar energy through photosynthesis.

In addition to faster fungal growth, the researchers noted changes in the electrical structure of the melanin exposed to radiation.

Lead researcher Ekaterina Dadachova said these observations suggest that the pigment may play a role in the fungi similar to that of chlorophyll in plants, which traps energy from sunlight and converts it to "food energy" needed to sustain life.

"We have associated the faster growth caused by radiation with melanin—a phenomenon suggesting that the pigment is somehow involved in harvesting high-energy ionizing radiation" and promoting growth, study co-author Arturo Casadevall of Yeshiva University said.

Duke University fungi expert Rytas Vilgalys, who was not involved in the study, said the new paper is "most interesting, truly original, and highly provocative."

The study by Dadachova's team was published today in the online journal PLoS One.

High-Energy Diet

The energy used by most living things is ultimately derived from sunlight, which is converted into simple sugars by plants and passed up the food chain.

Besides plants and photosynthetic bacteria, only a few organisms can fuel their own growth with energy obtained from nonbiological sources.

Last year, for example, scientists discovered bacteria living deep underground in a gold mine that harvest the energy of natural radioactivity.

If fungi containing melanin can do the same thing, the number of "self-feeding" organisms may be far greater than previously believed, the authors said.

"This observation raises the possibility that terrestrial life has another group of organisms capable of making their own food," study co-author Casadevall said.

"Given that fungi are such a large part of the biota, even a small energy-synthesizing capacity could have large effect on Earth's energy cycles," he added.

(See related: "Army of Tiny Fungi Keep Forests Healthy, Study Suggests" [November 21, 2005].)

Lead study author Dadachova also speculated the new source of biological energy could be useful to humans.

Space travelers, for example, could someday harvest foods raised on ionizing radiation, which is prevalent in outer space. Several edible mushrooms contain melanin.

In addition, "the genes from those fungi responsible for melanin production could be put into food-producing plants," she said.

Pigment Power

Melanin is widespread in nature and has long been known to provide protection from ultraviolet radiation, which in high exposures can cause skin cancer.

The pigment is present in most fungi and also accounts for skin color in humans.

"Melanin is pretty amazing stuff," said Duke's Vilgalys. "It's not surprising that many fungi have figured out how to use it for protection and possibly as a means to harvest [energy]."

John Dighton is a fungi specialist at Rutgers University in Camden, New Jersey, who has worked with a team of Ukrainian scientists studying fungi at Chernobyl.

He said the findings "confirm some of the thoughts we have been having for a few years."

"Fungi that have been previously exposed to ionizing radiation have a propensity to direct their growth towards sources [of the radiation]," Dighton said.

"We have suspected that cell-wall pigments, such as melanin, may be involved."

For now, lead author Dadachova said, the actual mechanism by which melanin captures and transforms high-energy radiation remains a mystery—though that's to be expected.

"For photosynthesis, it took decades for the mechanism to be understood."

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