May 23 (Bloomberg) -- Cockroaches may not be the sole survivors of a nuclear explosion after all. Some fungi benefit from high dosages of radiation and grow more readily as a result, researchers say.

Fungi that produce a pigment akin to the melanin that colors human skin grew ``significantly faster'' when exposed to radiation approximately 500 times higher than that in normal environments, researchers wrote in a paper published on line by the Public Library of Science's PLoS ONE.

Fungi -- a class of organisms that includes mushrooms and yeasts used to make beer and bread -- break down organic material. Previously, scientists hadn't realized that fungi can make their own food. This research indicates that other energy sources besides sunlight can be used for life.

``Melanotic organisms, like these fungi, are so primitive that they probably were around long before there were plants,'' said Arturo Casadevall, the chairman of the department of microbiology and immunology at the Albert Einstein College of Medicine at Yeshiva University. ``It's possible this is a very ancient pigment system that's been around a very long time.''

Most food comes from plants that convert sunlight into food using chlorophyll, Casadevall said in a telephone interview yesterday from the Bronx, New York, where the school is located. Other sources of sustenance have been discovered in the past, Casadevall said.

``We've discovered some other minor sources of energy like bugs that eat minerals, and bacteria that live on hydrothermal vents under the ocean, so far down the sun doesn't shine,'' he said. ``And now we've discovered another molecule that allows you to capture energy.''

Inspired by Chernobyl

The study was inspired by fungi growing on the radioactive reactor at Chernobyl, the Ukrainian power station that was the site of the worst nuclear accident 21 years ago.

``It's often said that the only survivors of a nuclear explosion would be cockroaches, whereas it's more likely that it would be fungi,'' said Steve Harris, an associate professor of plant pathology at the University of Nebraska in Lincoln. He wasn't involved in the study.

The range of places where fungi can live is ``remarkably diverse,'' Harris said in an e-mail yesterday. It could have been the case that the fungus happened to be especially hardy.

``To find that melanized fungi actually exploit the radiation to promote growth is unexpected,'' he said.

Casadevall urged caution in interpreting the results. That the fungi were ``eating'' the radiation didn't mean they were cleaning the radiation out of the sites, he said.

``What we know for sure is that radiation is associated with faster growth,'' he said. ``We are going to need to do a huge amount of research.''

To contact the reporter on this story: Elizabeth Lopatto in New York at elopatto@bloomberg.net

Last Updated: May 22, 2007 23:43 EDT