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A Self-Replicating Radiation-Shield for Human Deep-Space Exploration: Radiotrophic Fungi can Attenuate Ionizing Radiation aboard the International Space Station

By Graham K. Shunk, Xavier R. Gomez, Nils J. H. Averesch

Posted 17 Jul 2020
bioRxiv DOI: 10.1101/2020.07.16.205534

The greatest hazard for humans on deep-space exploration missions is radiation. To protect astronauts venturing out beyond Earth's protective magnetosphere and sustain a permanent presence across the solar system, advanced passive radiation protection is highly sought after. Due to the complex nature of space radiation, there is likely no one-size-fits-all solution to this problem, which is further aggravated by up-mass restrictions. In search of innovative radiation-shields, biotechnology appeals with suitability for in-situ resource utilization (ISRU), self-regeneration, and adaptability. Certain fungi thrive in high-radiation environments on Earth, such as the contamination radius of the Chernobyl Nuclear Power Plant. Analogous to photosynthesis, these organisms appear to perform radiosynthesis, utilizing the pigment melanin to harvest gamma-radiation and generate chemical energy. It is hypothesized that the dissipation of radiation by these organisms translates to a radiation shield. Here, growth of Cladosporium sphaerospermum and its capability to attenuate ionizing radiation, was studied aboard the International Space Station (ISS) over a period of 30 days, as an analog to habitation on the surface of Mars. At full maturity, radiation beneath a {approx} 1.7 mm thick lawn of the dematiaceous radiotrophic fungus (180{degrees} protection radius) was 2.17{+/-}0.25% lower as compared to the negative control. Based on an estimated growth advantage in space of ~ 20%, the reduction of radiation was attributed to the fungus' radiotropism and melanin-content. This was supported by calculations based on Lambert's law, where the melanin content of the biomass could be approximated to 8.6{+/-}0.9% [w/w]. The analysis of the experimental data was further complemented by an attenuation analysis subject to a Martian radiation environment scenario that put the shielding capacity of melanized (bio)materials into perspective. Compatible with ISRU, bio-based melanin-containing composites are promising as a means for radiation shielding while reducing overall up-mass, as is compulsory for future Mars-missions.

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