• Sara Laura Wilson

Thesis: Increased Biopolymer Pigment Production in Bacteria and Fungi Exposed to Ionizing Radiation

Updated: Jun 8

Mediated Matter Group at MIT Media Lab

Position: Undergraduate Researcher (UROP)

June 2019 — May 2020

Senior thesis accepted by Department of Materials Science and Engineering in fulfillment of the requirements for the degree of B.S. in Materials Science and Engineering at MIT

A major concern for manned space missions is ionizing radiation, which is known to pose both acute and chronic risks to many organisms. It is critical to expand strategies for radiation protection, including utilizing new materials and fabrication methods designed to support and augment health and wellbeing. The Mediated Matter Group in the Media Lab is researching the application of pigments for biocompatible radioprotection. These pigments’ properties—including both UV and ionizing radiation absorption—lend themselves to interesting potential applications in biomedicine and biotechnology. Some bacteria and fungi respond to ionizing radiation with enhanced growth and pigment production, and they have been found in a variety of extreme and high radiation environments. This thesis is an exploration of the potential of pigments, like melanins and carotenoids, to protect from and react to ionizing radiation in the context of space.

We defined parameters and physical setup to expose biological samples to experimental analogues of radiation profiles in low earth to deep space. After this exposure, we assess changes in growth, morphology, and material characteristics as compared to non-irradiated control samples.

Radiation exposure map with Co-60 sealed source from MIT Nuclear Reactor. Credit: Ed Lamere.

(a) A. niger, (b) B. subtilis, (c) N. crassa, (d) R. etli, (e) X. dendrorhous. In each image, the upper two petri dishes are controls; the bottom two petri dishes are experimental (seven-day irradiation from Co-60 source). Photos by Sara L. Wilson.

This study confirms that the fungi A. niger and N. crassa can be identified as Ionizing Radiation Resistant Microorganisms (IRRMs). These cultures thrived in on-Earth radiation studies, in which a Co-60 sealed source transmitted gamma radiation to the fungi. This study also supports that both melanins and carotenoids can be effective ionizing radiation shields, as A. niger produces melanin and N. crassa produces carotenoids. However, species with melanins were more prolific post-irradiation than those with carotenoids.

(a) Particulate composite with pigment clusters (brown) interspersed within the HDPE shield (yellow). (b) Laminated composite with alternating layers of HDPE and pigment. Graphic by Sara L. Wilson.

Extracted melanins and carotenoids could be implemented in high-density polyethylyene (HDPE), the most common radiation shield for space applications, to enhance the radiation shielding while addressing the detriments of HDPE, such as weight and rigidity. Multiple composite configurations should be considered to optimize binding between the extracted pigment and HDPE. HDPE is known to shield against neutron radiation, the most penetrative form of particulate radiation. The findings of this study conclude that biological pigments, particularly melanin, shields bacteria and fungi from gamma radiation, high-energy electromagnetic radiation. The combination of HDPE and melanin in a composite shield would protect against both forms of radiation. Additionally, melanin would protect against the secondary gamma radiation formed by high-energy ions. If applied to or woven into textiles, these pigments could also augment radiation shielding in fabrics.

Direct supervisor: Sunanda Sharma

PI: Neri Oxman

©2019 by Sara Laura Wilson.