The reactor's new residents
Five years after the 1986 Chernobyl nuclear disaster, scientists observed black fungi growing on the walls of the destroyed Reactor 4. In an environment with radiation levels 500 times higher than normal, these fungi were thriving. Researchers observed the fungal growths, or hyphae, actively growing towards the sources of highest radioactivity, a phenomenon named radiotropism. This discovery revealed a new class of extremophiles: radiotrophic fungi, organisms that appear to use deadly ionizing radiation as an energy source.
At least three species of these melanin-rich fungi have been identified inside the Chernobyl Exclusion Zone: Cladosporium sphaerospermum, Wangiella dermatitidis, and Cryptococcus neoformans. Studies at the Albert Einstein College of Medicine showed that these fungi grew faster when exposed to gamma radiation levels 500 times greater than background radiation. The reason for this ability is melanin, the same pigment that colors human skin. In these fungi, melanin absorbs ionizing radiation and converts it into a usable form of chemical energy. This process, termed radiosynthesis, is like how plants use chlorophyll to perform photosynthesis with sunlight. While the precise biochemical pathways are still under investigation, experiments show that radiation alters the electronic properties of the melanin, enabling this energy conversion.