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

Abstract

SUMMARY OF RECENT ADVANCESLife on Earth has always existed in the flux of ionizing radiation. However, fungi seem to interact with the ionizing radiation differently from other Earth's inhabitants. 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 microhomologymediated 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.

ANaganishiain high places: functioning populations or dormant cells from the atmosphere?

“…Whether or not these organisms are active in the air column is unknown, but there is the potential for global dispersal of members of Naganishia species via wind and cloud formations in the troposphere. Members of the N. albida clade have also been found in the International Space Station where high levels of ionising radiation are a persistent stressor (Dadachova and Casadevall 2008). …”

Compton Scattering by Internal Shields Based on Melanin-Containing Mushrooms Provides Protection of Gastrointestinal Tract from Ionizing Radiation

“…1 Many fungi, such as human pathogen Aspergillos niger, are black due to melanin presence, but the pigment is widespread among the edible fungi (mushrooms) as well. There are two major classes of melaninmelanins that do not contain sulfur in their structure are called eumelanins, while melanins which incorporate divalent Departments of 1 Radiology, 4 Physiology and Biophysics, 5 Medicine, 6 Pathology, sulfur are called pheomelanins 2 ( Fig. 1A, B).…”

“…Dramatic examples of such radiation protection are provided by the reports that melanized microorganisms are colonizing the highly radioactive environment inside the damaged nuclear reactor in Chernobyl, cooling pools in nuclear reactors, and space stations. 2 The mechanism of melanin interaction with ionizing radiation has remained largely unexplored, which prompted us to investigate this subject several years ago. Initially, we demonstrated that microbial melanin could function in transducing the energy of c radiation in fungal cells 3 and that the efficacy of the radioprotection of melanized cells by melanin was dependent on its chemical composition and spatial arrangement.…”

An Extended Dose–Response Model for Microbial Responses to Ionizing Radiation

“…There are examples of microbial species, such as Deinococcus radiodurans and Cryptococcus neoformans, that are adapted to highly radioactive environments (Cox and Battista, 2005;Zivanovic et al, 2009) and of melanin synthesizing fungi that have a greater ability to tolerate radioactivity than those that do not (Dadachova and Casadevall, 2008). Selection experiments have found that irradiation of Escherichia coli cells (up to 50 rounds) led to highly radio-resistant populations, and their genomic sequences unveiled nine genes prone to mutations (Harris et al, 2009;Byrne et al, 2014).…”