Ionizing radiation: how fungi cope, adapt, and exploit with the help of melanin

Abstract

Life on Earth has always existed in the flux of ionizing radiation. However, fungi seem to interact with the ionizing radiation differently from other inhabitants of the Earth. Recent data show that melanized fungal species like those from Chernobyl's reactor respond to ionizing radiation with enhanced growth. Fungi colonize space stations and adapt morphologically to extreme conditions. Radiation exposure causes upregulation of many key genes, and an inducible microhomology-mediated recombination pathway could be a potential mechanism of adaptive evolution in eukaryotes. The discovery of melanized organisms in high radiation environments, the space stations, Antarctic mountains, and in the reactor cooling water combined with phenomenon of 'radiotropism' raises the tantalizing possibility that melanins have functions analogous to other energy harvesting pigments such as chlorophylls.

Fig. 1

Mean return angle (±SE) of fungi when exposed to a collimated beam of gamma radiation from a ¹⁰⁹Cd source for 24 h (fungal isolates and sources in sequence are Penicillium roseopurpureum 147 Red Forest, P. lanosum reactor room, Paecilomyces liliacinus 101 unpolluted soil, P. lilacinus 1941 Red Forest, Penicillium hirsutum 3 hot particles, Cladosporium sphaerospermum 60 reactor room, C. cladosporioides unpolluted soil, C. sphaerospermum 3176 unpolluted soil, C. cladosporioides 10 reactor room). Adjacent histogram bars bearing the same letter are not significantly different at P=0.05 (reproduced with permission from ref. 17).

Fig. 2

Graphic representation of functional categories highly induced or reduced by X- and gamma-rays. The selected categories are presented as number of genes in each category in a time-course manner. (A) X-rays and (B) gamma-rays (reproduced with permission from ref. 30).