Could astronauts survive long space missions by eating mushrooms energized with cosmic rays? That's one possible implication of a new study suggesting that some fungi can use ionizing radiation as an energy source. More immediately, however, the research might help explain how some species of fungi survive in extreme environments.
Beginning in the early 1990s, microbiologist Nelli Zhdanova of the Institute of Microbiology and Virology in Kiev, Ukraine, and her colleagues published a series of reports on the dramatic growth of fungi on the walls of the damaged Chernobyl nuclear reactor and in the soil surrounding it. The group identified a startling number of fungal species there, around 200. Most contained the radiation-absorbing pigment melanin, which gives many fungi their dark color. (Melanin is also the primary pigment in human skin and hair, and helps protect skin against damage from ultraviolet light.) Melanin-containing fungi have also been found growing at high altitudes and in the Arctic and Antarctic regions where nutrients are scarce and ultraviolet light exposure is very strong.
The Chernobyl results by Zhdanova's group inspired a separate team at Albert Einstein College of Medicine in New York City to investigate further. Led by microbiologists Ekaterina Dadachova and Arturo Casadevall, the scientists first asked whether melanin takes part in metabolic reactions. They extracted melanin from Cryptococcocus neoformans, a yeast-like human pathogen that the team artificially induced to produce the pigment, and exposed it to ionizing radiation. The radiation energized electrons within the melanin and also increased 4-fold the pigment's ability to carry out a key metabolic oxidation reaction, the team reports in the 23 May issue of Public Library of Science ONE. When colonies of C. neoformans cells were directly exposed to radiation 500 times greater than normal background levels, they grew up to three times as fast. The team achieved similar results with two other species of fungi that naturally contain melanin, including one that was found at Chernobyl and another that infects human skin.
The team concluded that melanin-containing fungi may be able to use radiation as an energy source, especially under certain extreme conditions where nutrients are scarce but radiation levels are high. Since many edible mushrooms contain melanin, Dadachova says, space travelers might be able to survive by growing them in the ubiquitous cosmic rays found in outer space, as well as by consuming other plants which have been genetically engineered to contain melanin.
Tamas Torok, a microbiologist at the Lawrence Berkeley National Laboratory in Berkeley, California, says that the new work is "incredibly important" not only because it helps explain why fungi so easily colonized the Chernobyl reactor but also because it could alter our understanding of the role fungi play in bringing additional sources of energy into the earth's biosphere. But John Dighton, an ecologist at Rutgers University's Pinelands Field Station in New Lisbon, New Jersey, cautions that it is premature to conclude that the radiation is being used for metabolism, rather than some other biological function such as cell signaling. Dighton adds that the team's suggestion that melanized mushrooms could feed astronauts "is probably a little fanciful" because the mushrooms "would still need [other] nutritional sources."