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May 23, 2007
Zapped By Radiation, Fungi Flourish
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."
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