Lead Investigator: Kathryn Higley (Oregon State University)

Additional Investigators: Irene Marry, Steve Kustka, Jillian Newmyer (Oregon State University)

Project Objectives:

The goals of this project are to:

• Evaluate the potential for biocrust restoration or expansion;
• Assess biocrust capacity as a sustainable and affordable means for mitigating environmental contamination through stabilization/sequestration;
• Assess its potential to promote ecosystem resilience following drought, fire, or other disruptive events;
• Examine Cladosporium sphaerospermum (CS)’s mechanism of metabolism in high radiation fields;
• Construct mRNA libraries for strains of CS; and,
• Investigate CS’s potential as a bioremediation agent under radiation stress.

Significance/Impact:
EM manages many large swaths of land that contain very low concentrations of radionuclides at and beneath the soil surface. They also have constructed and operated low-level waste sites LLW at several facilities, including Idaho National Laboratory, Los Alamos National Laboratory, Oak Ridge Reservation, Savannah River Site, Hanford Site, and Nevada National Security Site (National Academies, 2017), which contain a range of radionuclides and activity concentrations. The design of covers for the waste sites is intended to manage water infiltration, minimize intrusion, and limit mobilization of the waste. Recent studies have shown that vegetative barriers may be superior in this water management effort (Benson, 2023). However, these sites are subject to disturbance from drought, fire, extreme rainfall, and other ecological disruptions, which can damage or remove surface vegetation. Restoration of surface vegetation as quickly as possible is necessary to ensure the integrity of the site. This research project is intended to assess the potential for biocrusts (Figure 1), melanin-pigmented fungi, or a combination of the two, to help stabilize vulnerable sites, enhance their resilience in the face of extreme events, and limit the mobilization of radionuclides in soils from beneath the surface (Haselwandter, 2020).

Biological soil crusts (“biocrusts”) (Figure 1) are intricate communities of cyanobacteria, lichens, mosses, fungi, and microorganisms that inhabit the uppermost layer of soil predominantly in arid and semi-arid ecosystems, but also in areas where plant-growth factors are less favorable (Sorochkina, et al. 2023). Their intricate networks of microorganisms stabilize soil through physical and biological processes which can prevent erosion through increased soil surface roughness and reduced velocity of overland water flow (Figure 2). Biocrusts can persist in dry soils due to their capacity to undergo dormancy during drought and tolerate complete desiccation. Biocrusts colonize the landscape before vascular plants after disturbance events (García-Carmona, 2023), facilitate seed germination (Haverilla, 2019), improve soil moisture and water-holding capacity, and overall increase soil fertility (Havrilla et al., 2019; Yadav, 2023). There is immense potential for utilizing biocrusts’ synergistic characteristics for restorative and sustainable means to mitigate and promote ecosystem resilience, therefore, requiring less human intervention. Restoration, expansion, or even introduction of biocrusts within contaminated sites may reduce human or environmental exposure by supporting native plant growth and enhancement of the density and robustness of ground cover.  There is also evidence to suggest that biocrusts may contribute to immobilization of contaminants within the soil matrix (Haselwandter, 2023).

Fungi are not only a prominent component of biocrusts (Elliott et al., 2024) but have been observed to thrive within highly radiologically contaminated environments. Cladosporium sphaerospermum (CS), a ubiquitous, melanin-rich and hyphae-producing fungi (Zalar et al., 2007), displays positive radiotrophism – an unusual behavior resulting in increased rates of sporulation and directional growth of hyphal biomass towards high-dose rate radiation sources (Tugay et al., 2006; Zhadanova et al., 2004). This behavior is allegedly sourced from a hypothetical metabolic pathway termed “radiosynthesis” that allows melanin-pigmented fungi to utilize ionizing radiation for cellular energy rather than carbon substrate (Dadachova et al., 2007). Subsequently, carbon substrate use can be optimized for cellular repair and biomass production (Geyer et al., 2016). The melanin pigment is also responsible for robust resistance against common EM site environmental stressors, including pH extremes, high concentrations of hazardous heavy metals and organic compounds, radionuclides, and nutrient scarcity (USGAO, 2023; Eisenman and Casadevall, 2012). One experiment studying the effectiveness of CS as a bioremediator suggested that fungi can utilize toluene, a common industrial chemical used in gaseous diffusion plants, as its sole source of carbon substrate through enzymatic digestion (Weber et al., 1995). This suggests the fungi have the potential for assimilating, degrading, or immobilizing persistent forms of environmental waste (Purkis et al., 2022; Manirethan et al., 2018; Mayans et al., 2011; Harms et al., 2011). Despite the potential for fungi exhibiting positive radiotrophism as effective bioremediators, major gaps in scientific literature require additional investigation.

References: (* indicates CRESP publication)

*Benson, C. H., Albright, W. H., Waugh, W. J., Apiwantragoon, P., Tigar, A. D., & Holbrook, D. L. (2023). Field Hydrology of Armored Earthen Final Covers with and without Vegetation.

Dadachova, E., Bryan, R. A., Huang, X., Moadel, T., Schweitzer, A. D., Aisen, P., Nosanchuk, J. D., & Casadevall, A. (2007). Ionizing Radiation Changes the Electronic Properties of Melanin and Enhances the Growth of Melanized Fungi. PLoS ONE, 2(5), e457. https://doi.org/10.1371/journal.pone.0000457

Doherty, K. D., Antoninka, A. J., Bowker, M. A., Ayuso, S. V., & Johnson, N. C. (2015). A Novel Approach to Cultivate Biocrusts for Restoration and Experimentation. Ecological Restoration, 33(1), 13–16. http://www.jstor.org/stable/43441702

Eisenman, H. C., & Casadevall, A. (2012). Synthesis and assembly of fungal melanin. Applied Microbiology and Biotechnology, 93(3), 931–940. https://doi.org/10.1007/s00253-011-3777-2

Elliott, D. R., Thomas, A. D., Hoon, S. R., & Sen, R. (2024). Spatial organization of fungi in soil biocrusts of the Kalahari is related to bacterial community structure and may indicate ecological functions of fungi in drylands. Frontiers in microbiology, 15, 1173637. https://doi.org/10.3389/fmicb.2024.1173637

García-Carmona, M., García-Orenes, F., Arcenegui, V., & Mataix-Solera, J. (2023). The Recovery of Mediterranean Soils After Post-Fire Management: The Role of Biocrusts and Soil Microbial Communities. Spanish Journal of Soil Science, 13, 11388. https://doi.org/10.3389/sjss.2023.11388

Geyer, K. M., Kyker-Snowman, E., Grandy, A. S., & Frey, S. D. (2016). Microbial carbon use efficiency: Accounting for population, community, and ecosystem-scale controls over the fate of metabolized organic matter. Biogeochemistry, 127(2), 173–188. https://doi.org/10.1007/s10533-016-0191-y

*Hargraves, J. T. (2023). Advancements in Phytoremediation, Dosimetry, and Environmental Radiological Protection: Integrating Endemic Plants, Anatomically Accurate Phantoms, and Real-world Data for Improved Assessments. PhD dissertation, Oregon State University.

Harms, H., Schlosser, D., & Wick, L. Y. (2011). Untapped potential: Exploiting fungi in bioremediation of hazardous chemicals. Nature Reviews Microbiology, 9(3), Article 3. https://doi.org/10.1038/nrmicro2519

Haselwandter, K., & Berreck, M. (2020). Accumulation of radionuclides in fungi. Metal ions in fungi, 259-278.

Havrilla CA, Chaudhary VB, Ferrenberg S, et al. Towards a predictive framework for biocrust mediation of plant performance: A meta-analysis. J Ecol. 2019; 107: 2789–2807. https://doi.org/10.1111/1365-2745.13269

Manirethan, V., Raval, K., Rajan, R., Thaira, H., & Balakrishnan, R. M. (2018). Kinetic and thermodynamic studies on the adsorption of heavy metals from aqueous solution by melanin nanopigment obtained from marine source: Pseudomonas stutzeri. Journal of Environmental Management, 214, 315–324. https://doi.org/10.1016/j.jenvman.2018.02.084

Mayans, B., Camacho-Arévalo, R., García-Delgado, C., Alcántara, C., Nägele, N., Antón-Herrero, R., Escolástico, C., & Eymar, E. (2021). Mycoremediation of Soils Polluted with Trichloroethylene: First Evidence of Pleurotus Genus Effectiveness. Applied Sciences, 11(4), Article 4. https://doi.org/10.3390/app11041354

National Academies of Sciences, Engineering, and Medicine; Division on Earth and Life Studies; Nuclear and Radiation Studies Board; Planning Committee on Low-Level Radioactive Waste Management and Disposition. (2017). Low-Level Radioactive Waste Management and Disposition: A Workshop [Report]. Washington, DC: National Academies Press.

Purkis, J. M., Bardos, R. P., Graham, J., & Cundy, A. B. (2022). Developing field-scale, gentle remediation options for nuclear sites contaminated with 137Cs and 90Sr: The role of Nature-Based Solutions. Journal of Environmental Management, 308, 114620. https://doi.org/10.1016/j.jenvman.2022.114620

Sorochkina, K., Nevins, C. J., Inglett, P. W., & Strauss, S. L. (2023). Biological Soil Crusts in Agroecosystems: SL506/SS719, 9/2023. EDIS, 2023(5). https://doi.org/10.32473/edis-SS719-2023

Tugay, T., Zhdanova, N. N., Zheltonozhsky, V., Sadovnikov, L., & Dighton, J. (2006). The influence of ionizing radiation on spore germination and emergent hyphal growth response reactions of microfungi. Mycologia, 98(4), 521–527. https://doi.org/10.3852/mycologia.98.4.521

US Government Accountability Office. (2023). Hanford Cleanup: DOE Should Validate Its Analysis of High-Level Waste Treatment Alternatives (Congressional Committee GAO-23-106093; p. 43). https://www.gao.gov/assets/gao-23-106093.pdf

Weber, F. J., Hage, K. C., & de Bont, J. A. (1995). Growth of the fungus Cladosporium sphaerospermum with toluene as the sole carbon and energy source. Applied and Environmental Microbiology, 61(10), 3562–3566.

Yadav, P., Singh, R. P., Hashem, A., Abd Allah, E. F., Santoyo, G., Kumar, A., & Gupta, R. K. (2023). Enhancing Biocrust Development and Plant Growth through Inoculation of Desiccation-Tolerant Cyanobacteria in Different Textured Soils. Microorganisms, 11(10), 2507. https://doi.org/10.3390/microorganisms11102507

Zalar, P., de Hoog, G. S., Schroers, H.-J., Crous, P. W., Groenewald, J. Z., & Gunde-Cimerman, N. (2007). Phylogeny and ecology of the ubiquitous saprobe Cladosporium  sphaerospermum, with descriptions of seven new species from hypersaline  environments. Studies in Mycology, 58, 157–183. https://doi.org/10.3114/sim.2007.58.06

Zhdanova, N. N., Tugay, T., Dighton, J., Zheltonozhsky, V., & Mcdermott, P. (2004). Ionizing radiation attracts soil fungi. Mycological Research, 108(9), 1089–1096. https://doi.org/10.1017/S0953756204000966