Relationships between radiation, wildfire and the soil microbial communities in the Chornobyl Exclusion Zone

There is considerable uncertainty regarding radiation's effects on biodiversity in natural complex ecosystems typically subjected to multiple environmental disturbances and stresses. In this study we characterised the relationships between soil microbial communities and estimated total absorbed dose rates to bacteria, grassy vegetation and trees in the Red Forest region of the Chornobyl Exclusion Zone. Samples were taken from sites of contrasting ecological histories and along burn and no burn areas following a wildfire. Estimated total absorbed dose rates to bacteria reached levels one order of magnitude higher than those known to affect bacteria in laboratory studies. Sites with harsher ecological conditions, notably acidic pH and low soil moisture, tended to have higher radiation contamination levels. No relationship between the effects of fire and radiation were observed. Microbial groups that correlated with high radiation sites were mostly classified to taxa associated with high environmental stress habitats or stress resistance traits. Distance-based linear models and co-occurrence analysis revealed that the effects of radiation on the soil microbiome were minimal. Hence, the association between high radiation sites and specific microbial groups is more likely a result of the harsher ecological conditions in these sites, rather than due to radiation itself. In this study, we provide a starting point for understanding the relationship between soil microbial communities and estimated total absorbed radiation dose rates to different components of an ecosystem highly contaminated with radiation. Our results suggest that soil microbiomes adapted to natural soil conditions are more likely to be resistant to ionising radiation than expected from laboratory studies, which demonstrates the importance of assessing the impact of ionising radiation on soil microbial communities under field conditions.

Deciphering Indigenous Bacterial Diversity of Co-Polluted Sites to Unravel Its Bioremediation Potential: A Metagenomic Approach

Polluted drains across the globe are affected due to reckless disposal of untreated industrial effluents resulting in significant water pollution affecting microbial community structure/dynamics. To elucidate this, polluted samples were collected from Budha Nala (BN) drain, Tung Dhab (TD) drain, and wastewater treatment plant (WWTP) receiving an inflow of organic pollutants as well as heavy metals due to anthropogenic activities. The sample of unpolluted pristine soil (PS) was used as control, as there is no history of usage of organic chemicals at this site. The bacterial diversity of these samples was sequenced using the Illumina MiSeq platform by amplifying the V3/V4 region of 16S rRNA. The majority of operational taxonomic unit (OTUs) at polluted sites belonged to phyla Proteobacteria specifically Gammaproteobacteria class, followed by Actinobacteria, Bacteriodetes, Chloroflexi, Firmicutes, Planctomycetes, WS6, and TM7, whereas unpolluted site revealed the prevalence of Proteobacteria followed by Actinobacteria, Planctomycetes, Firmicutes, Acidobacteria, Chloroflexi, Bacteroidetes, Verrucomicrobia, and Nitrospirae. The data sets decode unclassified species of the phyla Proteobacteria, Bacteriodetes, Chloroflexi, Firmicutes, and WS6, along with some unclassified bacterial species. The study provided a comparative study of changed microbial community structure, their possible functions across diverse geographical locations, and identifying specific bacterial genera as pollution bio-indicators of aged polluted drains.

Response of Microbial Communities to Naturally Occurring Radioactive Material-Contaminated Sediments: A Microcosm-Based Study

There is a growing need to understand the potential ecological impacts of contaminants in offshore oil and gas infrastructure, especially if that infrastructure is to be left in situ as a decommissioning option. Naturally occurring radioactive material (NORM) is one type of contaminant found in solid deposits on internal surfaces of infrastructure that poses potential ecological harm if released into the marine environment. Microbes are important components of marine sediment ecosystems because they provide ecosystem services, yet the impacts of NORM contamination to these communities are not well understood. The present study aimed to investigate the response of benthic microbial communities to NORM-contaminated scale, collected from an offshore oil and gas system, via controlled laboratory microcosm studies. Changes to microbial communities in natural sediment and sediments spiked with NORM at radium-226 activity concentrations ranging from 9.5 to 59.8 Bq/kg (in partial equilibria with progeny) over 7 and 28 days were investigated using high-throughput sequencing of environmental DNA extracted from experimental sediments. There were no significant differences in microbial community composition between control and scale-spiked sediments over 7 and 28 days. However, we observed a greater presence of Firmicutes in the scale-mixed treatment and Chloroflexi in the scale-surface treatments after 28 days. This could suggest selection for species with contaminant tolerance or potential resilience to radiation and metal toxicity. Further research is needed to explore microbial tolerance mechanisms and their potential as indicators of effects of radionuclide-contaminated sediments. The present study demonstrated that microcosm studies can provide valuable insights about the potential impacts of contamination from oil and gas infrastructure to sediment microbial communities. Environ Toxicol Chem 2024;43:1648-1661. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Microbiome analysis of the restricted bacteria in radioactive element-containing water at the Fukushima Daiichi Nuclear Power Station

A major incident occurred at the Fukushima Daiichi Nuclear Power Station following the tsunami triggered by the Tohoku-Pacific Ocean Earthquake in March 2011, whereby seawater entered the torus room in the basement of the reactor building. Here, we identify and analyze the bacterial communities in the torus room water and several environmental samples. Samples of the torus room water (1 × 109 Bq137Cs/L) were collected by the Tokyo Electric Power Company Holdings from two sampling points between 30 cm and 1 m from the bottom of the room (TW1) and the bottom layer (TW2). A structural analysis of the bacterial communities based on 16S rRNA amplicon sequencing revealed that the predominant bacterial genera in TW1 and TW2 were similar. TW1 primarily contained the genus Limnobacter, a thiosulfate-oxidizing bacterium. γ-Irradiation tests on Limnobacter thiooxidans, the most closely related phylogenetically found in TW1, indicated that its radiation resistance was similar to ordinary bacteria. TW2 predominantly contained the genus Brevirhabdus, a manganese-oxidizing bacterium. Although bacterial diversity in the torus room water was lower than seawater near Fukushima, ~70% of identified genera were associated with metal corrosion. Latent environment allocation-an analytical technique that estimates habitat distributions and co-detection analyses-revealed that the microbial communities in the torus room water originated from a distinct blend of natural marine microbial and artificial bacterial communities typical of biofilms, sludge, and wastewater. Understanding the specific bacteria linked to metal corrosion in damaged plants is important for advancing decommissioning efforts.

IMPORTANCE

In the context of nuclear power station decommissioning, the proliferation of microorganisms within the reactor and piping systems constitutes a formidable challenge. Therefore, the identification of microbial communities in such environments is of paramount importance. In the aftermath of the Fukushima Daiichi Nuclear Power Station accident, microbial community analysis was conducted on environmental samples collected mainly outside the site. However, analyses using samples from on-site areas, including adjacent soil and seawater, were not performed. This study represents the first comprehensive analysis of microbial communities, utilizing meta 16S amplicon sequencing, with a focus on environmental samples collected from the radioactive element-containing water in the torus room, including the surrounding environments. Some of the identified microbial genera are shared with those previously identified in spent nuclear fuel pools in countries such as France and Brazil. Moreover, our discussion in this paper elucidates the correlation of many of these bacteria with metal corrosion.

Taxonomic Diversity and Functional Traits of Soil Bacterial Communities under Radioactive Contamination: A Review

Studies investigating the taxonomic diversity and structure of soil bacteria in areas with enhanced radioactive backgrounds have been ongoing for three decades. An analysis of data published from 1996 to 2024 reveals changes in the taxonomic structure of radioactively contaminated soils compared to the reference, showing that these changes are not exclusively dependent on contamination rates or pollutant compositions. High levels of radioactive exposure from external irradiation and a high radionuclide content lead to a decrease in the alpha diversity of soil bacterial communities, both in laboratory settings and environmental conditions. The effects of low or moderate exposure are not consistently pronounced or unidirectional. Functional differences among taxonomic groups that dominate in contaminated soil indicate a variety of adaptation strategies. Bacteria identified as multiple-stress tolerant; exhibiting tolerance to metals and antibiotics; producing antioxidant enzymes, low-molecular antioxidants, and radioprotectors; participating in redox reactions; and possessing thermophilic characteristics play a significant role. Changes in the taxonomic and functional structure, resulting from increased soil radionuclide content, are influenced by the combined effects of ionizing radiation, the chemical toxicity of radionuclides and co-contaminants, as well as the physical and chemical properties of the soil and the initial bacterial community composition. Currently, the quantification of the differential contributions of these factors based on the existing published studies presents a challenge.

Assessing the chronic effect of the bioavailable fractions of radionuclides and heavy metals on stream microbial communities: A case study at the Rophin mining site

This study aimed to assess the potential impact of long-term chronic exposure (69 years) to naturally-occurring radionuclides (RNs) and heavy metals on microbial communities in sediment from a stream flowing through a watershed impacted by an ancient mining site (Rophin, France). Four sediment samples were collected along a radioactivity gradient (for 238U368 to 1710 Bq.Kg-1) characterized for the presence of the bioavailable fractions of radionuclides (226Ra, 210Po), and trace metal elements (Th, U, As, Pb, Cu, Zn, Fe). Results revealed that the available fraction of contaminants was significant although it varied considerably from one element to another (0 % for As and Th, 5-59 % for U). Nonetheless, microbial communities appeared significantly affected by such chronic exposure to (radio)toxicities. Several microbial functions carried by bacteria and related with carbon and nitrogen cycling have been impaired. The high values of fungal diversity and richness observed with increasing downstream contamination (H' = 4.4 and Chao1 = 863) suggest that the community had likely shifted toward a more adapted/tolerant one as evidenced, for example, by the presence of the species Thelephora sp. and Tomentella sp. The bacterial composition was also affected by the contaminants with enrichment in Myxococcales, Acidovorax or Nostocales at the most contaminated points. Changes in microbial composition and functional structure were directly related to radionuclide and heavy metal contaminations, but also to organic matter which also significantly affected, directly or indirectly, bacterial and fungal compositions. Although it was not possible to distinguish the specific effects of RNs from heavy metals on microbial communities, it is essential to continue studies considering the available fraction of elements, which is the only one able to interact with microorganisms.

Root-associated microbial community and diversity in napiergrass across radiocesium-contaminated lands after the Fukushima-Daiichi nuclear disaster in Japan

The microbiome derived from soil associated with plant roots help in plant growth and stress resistance. It exhibits potential benefits for soil remediation and restoration of radioactive-cesium (137Cs)-contaminated soils. However, there is still limited information about the community and diversity of root-associated microbiome in 137Cs-contaminated soil after the Fukushima-Daiichi Nuclear Power Plant (FDNPP) disaster. To address this, a comparative analysis of communities and diversity of root-associated microbiomes was conducted in two field types after the FDNPP disaster. In 2013, we investigated the community and diversity of indigenous root-associated microbiome of napiergrass (Pennisetum purpureum) grown in both grassland and paddy fields of 137Cs-contaminated land-use type within a 30-km radius around the FDNPP. Results showed that the root-associated bacterial communities in napiergrass belonged to 32 phyla, 75 classes, 174 orders, 284 families, and 521 genera, whereas the root-associated fungal communities belonged to 5 phyla, 11 classes, 31 orders, 59 families, and 64 genera. The most frequently observed phylum in both grassland and paddy field was Proteobacteria (47.4% and 55.9%, respectively), followed by Actinobacteriota (23.8% and 27.9%, respectively) and Bacteroidota (10.1% and 11.3%, respectively). The dominant fungal phylum observed in both grassland and paddy field was Basidiomycota (75.9% and 94.2%, respectively), followed by Ascomycota (24.0% and 5.8%, respectively). Land-use type significantly affected the bacterial and fungal communities that colonize the roots of napiergrass. Several 137Cs-tolerant bacterial and fungal taxa were also identified, which may be potentially applied for the phytoremediation of 137Cs-contaminated areas around FDNPP. These findings contribute to a better understanding of the distribution of microbial communities in 137Cs-contaminated lands and their long-term ecosystem benefits for phytoremediation efforts.

Plant-microorganism-soil interaction under long-term low-dose ionizing radiation

As the environmental nuclear radiation pollution caused by nuclear-contaminated water discharge and other factors intensifies, more plant-microorganism-soil systems will be under long-term low-dose ionizing radiation (LLR). However, the regulatory mechanisms of the plant-microorganism-soil system under LLR are still unclear. In this study, we study a system that has been stably exposed to low-dose ionizing radiation for 10 years and investigate the response of the plant-microorganism-soil system to LLR based on the decay of the absorbed dose rate with distance. The results show that LLR affects the carbon and nitrogen migration process between plant-microorganism-soil through the "symbiotic microbial effect." The increase in the intensity of ionizing radiation led to a significant increase in the relative abundance of symbiotic fungi, such as Ectomycorrhizal fungi and Rhizobiales, which is accompanied by a significant increase in soil lignin peroxidase (LiP) activity, the C/N ratio, and C%. Meanwhile, enhanced radiation intensity causes adaptive changes in the plant functional traits. This study demonstrates that the "symbiotic microbial effect" of plant-microorganism-soil systems is an important process in terrestrial ecosystems in response to LLR.

Prokaryotic communities inhabiting a high-radon subterranean ecosystem (Castañar Cave, Spain): Environmental and substrate-driven controls

Castañar Cave (Caceres, Spain) is a unique show cave known for its high natural radiation levels. This study presents a comprehensive analysis of its prokaryotic diversity, specifically focusing on investigating the influence of environmental conditions and substrate characteristics on the prokaryotic community structure in the cave sediments. Additionally, the research aims to evaluate the potential impact of human activities on the cave ecosystem. The identification of distinct bioclimatic zones within the cave was made possible through a combination of environmental and microbial monitoring (ATP assays). The results reveal sediment texture as a significant factor, notably affecting the structure, diversity, and phylogenetic variability of the microbial community, including both Bacteria and Archaea. The proportion of clay minerals in sediments plays a crucial role in regulating moisture levels and nutrient availability. These substrate properties collectively exert a significant selective pressure on the structure of prokaryotic communities within cave sediments. The molecular approach shows that heterotrophic bacteria, including those with chitinolytic enzymes, primarily inhabit the cave. Furthermore, chemoautotrophic nitrifiers such as the archaea Nitrososphaeria and the genus Nitrospira, as well as methanotrophic bacteria from the phyla Methylomirabilota, Pseudomonadota, and Verrucomicrobiota, are also present. Remarkably, despite being a show cave, the cave microbiota displays minimal impacts from human activities and the surface ecosystem. Prokaryotic populations exhibit stability in the innermost areas, while the tourist trail area experiences slightly higher biomass increases due to visitor traffic. This suggests that conservation efforts have successfully limited the entry of external nutrients into the innermost cave areas. Additionally, the results suggest that integrating biomarkers like ATP into environmental monitoring can significantly enhance the methods used to study the negative impacts of tourism on cave ecosystems.

Impact of ionizing radiation on the environmental microbiomes of Chornobyl wetlands

Radioactive contamination has the potential to cause damage to DNA and other biomolecules. Anthropogenic sources of radioactive contamination include accidents in nuclear power plants, such as the one in Chornobyl in 1986 which caused long-term radioactive pollution. Studies on animals within radioactive zones have provided us with a greater understanding of how wildlife can persevere despite chronic radiation exposure. However, we still know very little about the effects of radiation on the microbial communities in the environment. We examined the impact of ionizing radiation and other environmental factors on the diversity and composition of environmental microbiomes in the wetlands of Chornobyl. We combined detailed field sampling along a gradient of radiation together with 16 S rRNA high-throughput metabarcoding. While radiation did not affect the alpha diversity of the microbiomes in sediment, soil, or water, it had a significant effect on the beta diversity in all environment types, indicating that the microbial composition was affected by ionizing radiation. Specifically, we detected several microbial taxa that were more abundant in areas with high radiation levels within the Chornobyl Exclusion Zone, including bacteria and archaea known to be radioresistant. Our results reveal the existence of rich and diverse microbiomes in Chornobyl wetlands, with multiple taxonomic groups that are able to thrive despite the radioactive contamination. These results, together with additional field and laboratory-based approaches examining how microbes cope with ionizing radiation will help to forecast the functionality and re-naturalization dynamics of radiocontaminated environments.

The interplay between Cs and K in Pseudanabaena catenata; from microbial bloom control strategies to bioremediation options for radioactive waters

Pseudanabaena dominates cyanobacterial blooms in the First-Generation Magnox Storage Pond (FGMSP) at a UK nuclear site. The fission product Cs is a radiologically significant radionuclide in the pond, and understanding the interactions between Cs and Pseudanabaena spp. is therefore important for determining facility management strategies, as well as improving understanding of microbiological responses to this non-essential chemical analogue of K. This study evaluated the fate of Cs following interactions with Pseudanabaena catenata, a laboratory strain most closely related to that dominating FGMSP blooms. Experiments showed that Cs (1 mM) exposure did not affect the growth of P. catenata, while a high concentration of K (5 mM) caused a significant reduction in cell yield. Scanning transmission X-ray microscopy elemental mapping identified Cs accumulation to discrete cytoplasmic locations within P. catenata cells, indicating a potential bioremediation option for Cs. Proteins related to stress responses and nutrient limitation (K, P) were stimulated by Cs treatment. Furthermore, selected K⁺ transport proteins were mis-regulated by Cs dosing, which indicates the importance of the K⁺ transport system for Cs accumulation. These findings enhance understanding of Cs fate and biological responses within Pseudanabaena blooms, and indicate that K exposure might provide a microbial bloom control strategy.

Effect of Radium-223 on the Gut Microbiota of Prostate Cancer Patients: A Pilot Case Series Study

Radium-223 (Ra-223) is a targeted nuclear medicine therapy for castration-resistant prostate cancer with bone metastases. Its major route of elimination is the intestine. There is overwhelming evidence that the gut microbiota is altered by ionizing radiation (IR) from radiotherapy treatments. Nevertheless, it is known that extrapolation of outcomes from radiotherapy to nuclear medicine is not straightforward. The purpose of this study was to prospectively determine the effect of Ra-223 on selected important bacteria from the gut microbiota. Stool samples from three prostate cancer patients and two healthy individuals were obtained, processed, and analysed. We specifically measured the relative change of the abundance of important bacteria, determined by the 2^−ΔΔC method. We found that Ra-223 influenced the gut microbiota composition. The most relevant changes were increases of Proteobacteria and Atopobacter; and decreases of Bacteroidetes, Prevotella, Lactobacillus, Bifidobacterium, Clostridium coccoides, and Bacteroides fragilis. Additionally, our experiment confirms that the composition of gut microbiota from prostate cancer patients is altered. No significant correlation was found between each subject’s gut microbiome profile and their clinical indices. Despite its limited sample, the results of this pilot study suggest that ionizing radiation from Ra-223 alters the gut microbiota composition and that the gut microbiota of prostate cancer patients has an increase of the bacteria with known prejudicial effects and a decrease of the ones with favorable effects.

Ionizing Radiation from Radiopharmaceuticals and the Human Gut Microbiota: An Ex Vivo Approach

This study aimed to determine the effect of three widely used radiopharmaceuticals with intestinal excretion on selected relevant bacteria that are part of the human gut microbiota, using an ex vivo approach. Fecal samples obtained from healthy volunteers were analyzed. Each sample was divided into four smaller aliquots. One served as the non-irradiated control. The other three were homogenized with three radiopharmaceutical solutions ([¹³¹I]NaI, [^99mTc]NaTcO₄, and [²²³Ra]RaCl₂). Relative quantification of each taxa was determined by the 2^−ΔΔC method, using the ribosomal gene 16S as an internal control (primers 534/385). Twelve fecal samples were analysed: three controls and nine irradiated. Our experiment showed fold changes in all analyzed taxa with all radiopharmaceuticals, but results were more significant with I-131, ranging from 1.87–83.58; whereas no relevant differences were found with Tc-99m and Ra-223, ranging from 0.98–1.58 and 0.83–1.97, respectively. This study corroborates limited existing research on how ionizing radiation changes the gut microbiota composition, providing novel data regarding the ex vivo effect of radiopharmaceuticals. Our findings justify the need for future larger scale projects.

Characterization of Microbial Communities and Naturally Occurring Radionuclides in Soilless Growth Media Amended with Different Concentrations of Biochar

Biochar, derived from the pyrolysis of plant materials has the potential to enhance plant growth in soilless media. Howevetar, little is known about the impact of biochar amendments to soilless growth media, microbial community composition, and fate of chemical constituents in the media. In this study, different concentrations of biochar were added to soilless media and microbial composition, and chemical constituents were analyzed using metagenomics and gamma spectroscopy techniques, respectively. Across treatments, carboxyl-C, phenolic-C, and aromatic-C were the main carbon sources that influenced microbial community composition. Flavobacterium (39.7%), was the predominantly bacteria genus, followed by Acidibacter (12.2%), Terrimonas (10.1%), Cytophaga (7.5%), Ferruginibacter (6.0%), Lacunisphaera (5.9%), Cellvibrio (5.8%), Opitutus (4.8%), Mucilaginibacter (4.0%) and Bryobacter (4.0%). Negative relationships were found between Cytophaga and 226Ra (r = −0.84, p = 0.0047), 40K (r = −0.82, p = 0.0069) and 137Cs (r = −0.93, p = 0.0002). Similarly, Mucilaginibacter was negatively correlated with 226Ra (r = −0.83, p = 0.0054) and 137Cs (r = −0.87, p = 0.0021). Overall, the data suggest that high % biochar amended samples have high radioactivity concentration levels. Some microorganisms have less presence in high radioactivity concentration levels.

A new era of radiation resistance bacteria in bioremediation and production of bioactive compounds with therapeutic potential and other aspects: An in-perspective review

Microorganisms that survive in extreme environmental conditions are known as 'extremophiles'. Recently, extremophiles draw an impression in biotechnology/pharmaceutical researches/industries because of their novel molecules, known as 'extremolytes'. The intriguing phenomenon of microbial radiation resistance probably arose independently throughout their evolution of selective pressures (e.g. UV, X-ray, Gamma radiation etc.). Radiation produces multiple types of damage/oxidation to nucleic acids, proteins and other crucial cellular components. Most of the literature on microbial radiation resistance is based on acute γ-irradiation experiments performed in the laboratory, typically involving pure cultures isolation and their application on bioremediation/therapeutic field. There is much less information other than bioremediation and therapeutic application of such promising microbes we called as 'new era'. Here we discus origin and diversity of radiation resistance bacteria as well as selective mechanisms by which microorganisms can sustain in radiation rich environment. Potential uses of these radiations resistant microbes in the field of bioremediation, bioactive compounds and therapeutic industry. Last but not the least, which is the new aspect of radiation resistance microbes. Our review suggest that resistance to chronic radiation is not limited to rare specialized strains from extreme environments, but can occur among common microbial taxa, perhaps due to overlap molecular mechanisms of resistance to radiation and other stressors. These stress tolerance potential make them potential for radionuclides remediation, their extremolytes can be useful as anti-oxidant and anti-proliferative agents. In current scenario they can be useful in various fields from natural dye synthesis to nanoparticles production and anti-cancer treatment.

Comparable response of wild rodent gut microbiome to anthropogenic habitat contamination

Species identity is thought to dominate over environment in shaping wild rodent gut microbiota, but it remains unknown whether the responses of host gut microbiota to shared anthropogenic habitat impacts are species-specific or if the general gut microbiota response is similar across host species. Here, we compare the influence of exposure to radionuclide contamination on the gut microbiota of four wild mouse species: Apodemus flavicollis, A. sylvaticus, A. speciosus and A. argenteus. Building on the evidence that radiation impacts bank vole (Myodes glareolus) gut microbiota, we hypothesized that radiation exposure has a general impact on rodent gut microbiota. Because we sampled (n = 288) two species pairs of Apodemus mice that occur in sympatry in habitats affected by the Chernobyl and Fukushima nuclear accidents, these comparisons provide an opportunity for a general assessment of the effects of exposure to environmental contamination (radionuclides) on gut microbiota across host phylogeny and geographical areas. In general agreement with our hypothesis, analyses of bacterial 16S rRNA gene sequences revealed that radiation exposure alters the gut microbiota composition and structure in three of the four species of Apodemus mice. The notable lack of an association between the gut microbiota and soil radionuclide contamination in one mouse species from Fukushima (A. argenteus) probably reflects host "radiation escape" through its unique tree-dwelling lifestyle. The finding that host ecology can modulate effects of radiation exposure offers an interesting counterpoint for future analyses into effects of radiation or any other toxic exposure on host and its associated microbiota. Our data show that exposure to radionuclide contamination is linked to comparable gut microbiota responses across multiple species of rodents.

Microbial interaction with and tolerance of radionuclides: underlying mechanisms and biotechnological applications

Radionuclides (RNs) generated by nuclear and civil industries are released in natural ecosystems and may have a hazardous impact on human health and the environment. RN-polluted environments harbour different microbial species that become highly tolerant of these elements through mechanisms including biosorption, biotransformation, biomineralization and intracellular accumulation. Such microbial-RN interaction processes hold biotechnological potential for the design of bioremediation strategies to deal with several contamination problems. This paper, with its multidisciplinary approach, provides a state-of-the-art review of most research endeavours aimed to elucidate how microbes deal with radionuclides and how they tolerate ionizing radiations. In addition, the most recent findings related to new biotechnological applications of microbes in the bioremediation of radionuclides and in the long-term disposal of nuclear wastes are described and discussed.

Direct comparison of bacterial communities in soils contaminated with different levels of radioactive cesium from the first Fukushima nuclear power plant accident

The Great East Japan Earthquake caused a serious accident at the first Fukushima nuclear power plant (NPP), which in turn released a large amount of radionuclides. Little attention has been paid to in-situ soil microorganisms exposed to radioactive contamination by the actual NPP accident. We herein investigated bacterial communities in the radioactive cesium (Cs)-contaminated and non-contaminated soils by high-throughput sequencing. The uppermost and ectorhizosphere soil samples were collected from the base of mugwort grown in the same soil type with the same soil-use history in order to compare the bacterial communities at geographically separated areas. The concentrations of radioactive Cs in the soils ranged from 10 to 563,000 Bq ¹³⁷Cs/kg dry soil, with the highest concentration being detected at 1 km from the NPP. Alpha-diversity indices, i.e., Chao1, Shannon and Simpson reciprocal, of the sequence data showed the lower bacterial diversity in the most highly Cs-contaminated soil. Principal coordinate analysis with principle components 1 and 3 based on unweighted UniFrac distances indicated the significant difference in bacterial communities of the most contaminated area from those of the other areas. Operational taxonomic unit-based assay revealed higher abundance of the radio-resistant Geodermatophilus bullaregiensis relative in the most contaminated soil. Thus, it was strongly suggested that the radioactive accident facilitated the growth and/or survival of radio-resistant bacteria in the Cs-contaminated soils. The results of this study show that information on the soil type, vegetation and soil-use history enhances the direct comparison of geographically distant soil bacterial communities exposed to different levels of radioactive contamination.