Ionizing Radiation Changes the Electronic Properties of Melanin and Enhances the Growth of Melanized Fungi (original) (raw)
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Environmental microbiology, 2017
Melanin is a ubiquitous pigment with unique physicochemical properties. The resistance of melanized fungi to cosmic and terrestrial ionizing radiation suggests that melanin also plays a pivotal role in radioprotection. In this study, we compared the effects of densely-ionizing deuterons and sparsely-ionizing X-rays on two microscopic fungi capable of melanogenesis. We utilized the fast-growing pathogenic basiodiomycete forming an induced DOPA-melanin, Cryptococcus neoformans (CN); and the slow-growing environmental rock-inhabiting ascomycete synthesizing a constitutive DHN-melanin, Cryomyces antarcticus (CA); melanized and non-melanized counterparts were compared. CA was more resistant to deuterons than CN, and similar resistance was observed for X-rays. Melanin afforded protection against high-dose (1.5 kGy) deuterons for both CN and CA (p-values < 10(-4) ). For X-rays (0.3 kGy), melanin protected CA (p-values < 10(-4) ) and probably CN. Deuterons increased XTT activity in me...
Pigment Cell & Melanoma Research, 2007
Melanized microorganisms are often found in environments with very high background radiation levels such as in nuclear reactor cooling pools and the destroyed reactor in Chernobyl. These findings and the laboratory observations of the resistance of melanized fungi to ionizing radiation suggest a role for this pigment in radioprotection. We hypothesized that the radioprotective properties of melanin in microorganisms result from a combination of physical shielding and quenching of cytotoxic free radicals. We have investigated the radioprotective properties of melanin by subjecting the human pathogenic fungi Cryptococcus neoformans and Histoplasma capsulatum in their melanized and non-melanized forms to sublethal and lethal doses of radiation of up to 8 kGy. The contribution of chemical composition, free radical presence, spatial arrangement, and Compton scattering to the radioprotective properties of melanin was investigated by high-performance liquid chromatography, electron spin resonance, transmission electron microscopy, and autoradiographic techniques. Melanin protected fungi against ionizing radiation and its radioprotective properties were a function of its chemical composition, free radical quenching, and spherical spatial arrangement.
Pigment Cell Melanoma Research, 2007
Melanized microorganisms are often found in environments with very high background radiation levels such as in nuclear reactor cooling pools and the destroyed reactor in Chernobyl. These findings and the laboratory observations of the resistance of melanized fungi to ionizing radiation suggest a role for this pigment in radioprotection. We hypothesized that the radioprotective properties of melanin in microorganisms result from a combination of physical shielding and quenching of cytotoxic free radicals. We have investigated the radioprotective properties of melanin by subjecting the human pathogenic fungi Cryptococcus neoformans and Histoplasma capsulatum in their melanized and non-melanized forms to sublethal and lethal doses of radiation of up to 8 kGy. The contribution of chemical composition, free radical presence, spatial arrangement, and Compton scattering to the radioprotective properties of melanin was investigated by high-performance liquid chromatography, electron spin resonance, transmission electron microscopy, and autoradiographic techniques. Melanin protected fungi against ionizing radiation and its radioprotective properties were a function of its chemical composition, free radical quenching, and spherical spatial arrangement.
Microbial melanin physiology under stress conditions and gamma radiation protection studies
Radiation Physics and Chemistry, 2019
Any life-threatening alteration in environmental circumstances from the optimal imposes stress on an organism. Microorganisms possess various strategies, including pigment production, to resist stress conditions in their surrounding environments. In the present study, yeast form of fungus Aureobasidium pullulans either melanized or albino was exposed to different stresses, such as salinity and antifungals (fluconazole, itraconazole, and terbinafine) as well as gamma irradiation. Results revealed that at 800 µg/ml or less of antifungal terbinafine, a positive impact was achieved on the viability of A. pullulans yeast cells, in the cultivation medium wasn't supplemented with melanin precursor (L-3,4 dihydroxyphenylalanine; L-DOPA). This enhancement in the growth yield was accompanied by increases in both internal and external melanin yields by eight and six folds, respectively. In addition, melanin is synthesized during terbinafine stress in a pathway independent from L-DOPA, but based on the excess of acetyl-CoA to tolerate squalene accumulation by feedback inhibition. Moreover, the melanized yeast cells show greater viable stability against gamma irradiation as well as pigment productivity than albino cells. The main objective of this study is to create new composites to use them as shielding materials. Theses composites based on fungal melanin's chelating activity with nanoparticles of bismuth, lead, and silver. The mass attenuation coefficient of Melanin-Bismuth composite is nearly double the mass attenuation of lead at energy = 0.662 MeV; a higher increase in mass attenuation is observed with higher gamma intensities; 1.17 and 1.33 MeV. Coupling synthesis of composites containing natural microbial products with nanotechnology is a promising field to manufacture new radiation shielding materials.
Journal of Environmental Radioactivity, 2019
Ectomycorrhizal (EM) fungi form symbioses with dominant tree families in boreal, temperate and tropical ecosystems and are important drivers of ecosystem function. EM fungal hyphae extend over a large area making them susceptible to enhanced radiation levels from naturally occurring or anthropogenically originating radioisotopes in the rhizosphere. In this study, the in-vitro effects of ionizing radiation on the growth and biomass of EM fungi Suillus luteus, S. bovinus and Rhizopogon luteolus were investigated. EM fungal cultures were exposed to gamma radiation from a 137 Cs source for 137 h in darkness at 21°C at dose rates of 404, 108.5 and 54.9 mGy h −1 resulting in total absorbed doses of 55.21, 14.82 and 7.50 Gy respectively. Cultures grown in the dark at 21°C but not exposed to the 137 Cs source served as the control. Our results show that EM fungi vary in their sensitivity to ionizing radiation. EM fungi used in this study produced melanin and reactive oxygen species scavenging enzymes such as catalase and superoxide dismutase as a response to ionizing radiation.
A biomimetic approach to shielding from ionizing radiation: The case of melanized fungi
PLOS ONE, 2020
Melanized fungi have been shown to thrive in environments with high radionuclide concentrations, which led to the association of the pigment melanin with the protection against ionizing radiation. Several hypotheses regarding the function of melanin have been proposed. Yet, the exact mechanism behind the protective property of melanin is unclear and poorly explored. A better understanding of the mechanisms that are involved in increasing the tolerance of the organisms to ionizing radiation could lead to technology transfer to humanrelated applications. Effective protection from radiation is essential for human space flight in general and human missions beyond Low Earth Orbit specifically. In this paper, we follow a biomimetic approach: we test two of current hypotheses and discuss how they could be applied to radiation shield designs. First we focus on the interaction of melanin with high energy electrons, which has been suspected to reduce the kinetic energy of the electrons through a cascade of collisions, thus providing physical shielding. Second, we investigate if the spatial arrangement of melanin, organized as a thin film or a collection of hollow microspheres, affects its shielding properties. To this end, we measured experimentally and by numerical simulations the attenuation of β-radiation as pass through solutions and suspensions of melanin and contrasted the values to the ones of cellulose, a substance with similar elemental composition. Further, we investigate the spatial arrangement hypothesis using Monte Carlo simulations. In agreement with the simulations, our experiments indicated that melanin does not provide improved shielding in comparison to cellulose from β-radiation. However, our simulations suggest a substantial effect of the spatial arrangement on the shielding performance of melanin, a pathway that could be transferred to the design of composite radiation shields.
Mathematical Modeling Predicts Enhanced Growth of X-Ray Irradiated Pigmented Fungi
PLoS ONE, 2014
Ionizing radiation is known for its cytotoxic and mutagenic properties. However, recent evidence suggests that chronic sublethal irradiation stimulates the growth of melanin-pigmented (melanized) fungi, supporting the hypothesis that interactions between melanin and ionizing photons generate energy useful for fungal growth, and/or regulate growthpromoting genes. There are no quantitative models of how fungal proliferation is affected by ionizing photon energy, dose rate, and presence versus absence of melanin on the same genetic background. Here we present such a model, which we test using experimental data on melanin-modulated radiation-induced proliferation enhancement in the fungus Cryptococcus neoformans, exposed to two different peak energies (150 and 320 kVp) over a wide range of X-ray dose rates. Our analysis demonstrates that radiation-induced proliferation enhancement in C. neoformans behaves as a binary ''on/off'' phenomenon, which is triggered by dose rates ,0.002 mGy/h, and stays in the ''on'' position. A competing dose rate-dependent growth inhibition becomes apparent at dose rates .5000 mGy/h. Proliferation enhancement of irradiated cells compared with unirradiated controls occurs at both X-ray peak energies, but its magnitude is modulated by X-ray peak energy and cell melanization. At dose rates ,5000 mGy/h, both melanized and non-melanized cells exposed to 150 kVp Xrays, and non-melanized cells exposed to 320 kVp X-rays, all exhibit the same proliferation enhancement: on average, chronic irradiation stimulates each founder cell to produce 100 (95% CI: 83, 116) extra descendants over 48 hours. Interactions between melanin and 320 kVp X-rays result in a significant (2-tailed p-value = 4.8610 25 ) additional increase in the number of radiation-induced descendants per founder cell: by 55 (95% CI: 29, 81). These results show that both melanindependent and melanin-independent mechanisms are involved in radiation-induced fungal growth enhancement, and implicate direct and/or indirect interactions of melanin with high energy ionizing photons as an important pro-proliferative factor.
Environmental microbiology reports, 2018
The aim of this study was to analyse how protracted exposure to X-rays delivered at low dose rates of 0.0032-0.052 kGy h affects the survival and metabolic activity of two microfungi capable of melanogenesis: fast-growing Cryptococcus neoformans (CN) and slow-growing Cryomyces antarcticus (CA). Melanized CN and CA cells survived the protracted exposure better than non-melanized ones, which was consistent with previous reports on the radioprotective role of melanin in these fungi after high dose rate exposures. The survival data were described by the linear quadratic dose response model. The XTT metabolic profiles were practically identical for melanized CN and CA with activity dose-dependent increasing: no changes in the activity of the non-melanized CN and CA were recorded by this assay. In contrast, the MTT assay, which measures the intracellular energy-related processes, recorded an increase in activity of non-melanized CN and CA cells, but not in their melanized counterparts. Th...