Melanin, Radiation, and Energy Transduction in Fungi

Abstract

Melanin pigments are found in many diverse fungal species, where they serve a variety of functions that promote fitness and cell survival. Melanotic fungi inhabit some of the most extreme habitats on earth such as the damaged nuclear reactor at Chernobyl and the highlands of Antarctica, both of which are high-radiation environments. Melanotic fungi migrate toward radioactive sources, which appear to enhance their growth. This phenomenon, combined with the known capacities of melanin to absorb a broad spectrum of electromagnetic radiation and transduce this radiation into other forms of energy, raises the possibility that melanin also functions in harvesting such energy for biological usage. The ability of melanotic fungi to harness electromagnetic radiation for physiological processes has enormous implications for biological energy flows in the biosphere and for exobiology, since it provides new mechanisms for survival in extraterrestrial conditions. Whereas some features of the way melanin-related energy transduction works can be discerned by linking various observations and circumstantial data, the mechanistic details remain to be discovered.

FIGURE 1

Melanized Cryptococcus neoformans and melanin “ghosts.” (A) Melanized C. neoformans cell in India Ink suspension to illustrate the cellular location of melanin. The cell wall appears dark because of the presence of melanin. Note that melanin is external to the body of the cell. (B) Melanin ghosts prepared from melanized cryptococcal cells by strong acid digestion (38), which removes cellular components except for the cell wall-associated melanin. (C) Scanning electron microscopy of a melanin ghost showing its granulated surface structure, porosity, and thickness.