What is Radiotrophic Fungus?

All living things need energy in order to grow and thrive. This energy, which originates from the sun, is harnessed by plants and stored in the form of sugars. Members of the animal kingdom like us then eat the energy-rich molecules in plant matter and we grow and thrive as a result. Members of kingdom Fungi do things a little differently, especially one in particular.

While fungi typically absorb their nutrition from other living organisms, one fungus has a way of surviving that seems to be straight out of a sci-fi movie. It is called 'radiotrophic fungus', and it appears to gain energy from a highly unusual source: ionizing radiation.

A symbol of radiation from nuclear meltdown

You may hear the word 'radiation' and think danger. Although we are bombarded on a daily basis by normal levels of the sun's radiation, there are much worse types. Ionizing radiation is the kind to avoid, found at nuclear waste sites which are fortunately not frequented by people. At high levels, this radiation causes cancer and possibly death. So how can an organism possibly use this form of energy to live? In this lesson, learn more about the way in which the tough and adaptable radiotrophic fungus uses radiation.

Radiotrophic Fungus at Chernobyl

When the nuclear reactor at Chernobyl melted down in 1986, extremely dangerous levels of ionizing radiation were emitted. Every living thing in the vicinity either fled or succumbed to the devastation. So scientists were intrigued when they returned to the site and found life in the form of black fungus covering the walls of the reactor. And it wasn't just a sparse few, but entire colonies had taken up residence and were happily thriving. It was clear that these fungi were not only spared damage from the radiation, but were somehow using it to their advantage.

The question became, what made this fungus special and able to survive this high level of radiation and use it to grow? Let's take a closer look at fungi as we explore this strange phenomenon.

First of all, fungi are heterotrophic. This means that they cannot make their own food through photosynthesis like plants do. Second, fungi are decomposers, attaching themselves to other living organisms and absorb their nutrients. You have undoubtedly found mushrooms eating their way through damp fallen logs deep in the forest. It was clear that the radiotrophic fungi were not absorbing nutrition this way as they were growing on the cement walls.

Example of a fungus growing on a log

As scientists further investigated, they found that the radiotrophic fungi had a common feature. They were all dark in color, indicating large concentrations of the pigment melanin. Melanin (Greek for ''black'') is also found in our skin, with higher concentrations producing darker skin colors. If you enjoy a luxuriously dark tan in the summer, you have plenty of melanin. Melanin acts as a natural sunblock, absorbing the sun's ultraviolet rays and protecting the skin cells. So was the melanin somehow responsible for the utilization of radiation in these fungi?

To better understand, a team of scientists led by microbiologist Arturo Casadevall performed a set of experiments in which they exposed black fungus as well as albino varieties to high levels of radiation. Sure enough, those black fungi which were exposed to the highest levels of radiation grew the most. So a theory quickly developed, stating that the melanin had some function in harnessing the energy from this otherwise deadly radiation.