Response of soil microbial communities to natural radionuclides along specific-activity gradients

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.

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.

Microbial consortium and impact of industrial mining on the Natural High Background Radiation Area (NHBRA), India - Characteristic role of primordial radionuclides in influencing the community structure and extremophiles pattern

The present investigation is the first of its kind which aims to study the characteristics of microbial consortium inhabiting one of the natural high background radiation areas of the world, Chavara Coast in Kerala, India. The composition of the microbial community and their structural changes were evaluated under the natural circumstances with exorbitant presence of radionuclides in the sediments and after the radionuclide's recession due to mining effects. For this purpose, the concentration of radionuclides, heavy metals, net radioactivity estimation via gross alpha and beta emitters and other physiochemical characteristics were assessed in the sediments throughout the estuarine stretch. According to the results, the radionuclides had a significant effect in shaping the community structure and composition, as confirmed by the bacterial heterogeneity achieved between the samples. The results indicate that high radioactivity in the background environment reduced the abundance and growth of normal microbial fauna and favoured only the growth of certain extremophiles belonging to families of Piscirickettsiacea, Rhodobacteriacea and Thermodesulfovibrionaceae, which were able to tolerate and adapt towards the ionizing radiation present in the environment. In contrast, communities from Comamondacea, Sphingomonadacea, Moraxellacea and Erythrobacteracea were present in the sediments collected from industrial outlet, reinforcing the potent role of radionuclides in governing the community pattern of microbes present in the natural environment. The study confirms the presence of these novel and unidentified bacterial communities and further opens the possibility of utilizing their usefulness in future prospects.

Bioremediation of uranium (Ⅵ) using a native strain Halomonas campaniensis ZFSY-04 isolated from uranium mining and milling effluent: Potential and mechanism

A significant surge in the exploitation of uranium resources has resulted in considerable amounts of radioactive effluents. Thus, efficient and eco-friendly uranium removal strategies need to be explored to ensure ecological safety and resource recovery. In this study, we investigated the resistance of Halomonas campaniensis strain ZFSY-04, isolated from an evaporation pool at a uranium mine site, and its potential mechanism of uranium (Ⅵ) removal. The results showed that the strain exhibited unique uranium tolerance and its growth was not significantly inhibited under a uranium concentration of 700 mg/L. It had a maximum loading capacity of 865.40 mg/g (dry weight), achieved following incubation under uranium concentration of 100 mg/L, pH 6.0, and temperature 30 °C, for 2 h, indicating that the removal of uranium by the strain was efficient and rapid. Combined with kinetic, isothermal, thermodynamic, and microspectral analyses, the mechanism of uranium loading by strain ZFSY-04 was metabolism-dependent and diverse, including, physical and chemical adsorption on the cell surface, extracellular biomineralisation, intracellular bioaccumulation, and biomineralisation. Our results highlight the unique properties of indigenous strains, including high resistance, high efficiency, rapid uranium removal, and various uranium removal strategies, which make it suitable as a new tool for in situ bioremediation and uranium-contaminated environmental resource recovery.

Remedial effect and operating status of a decommissioned uranium mill tailings (UMT) repository: A micro-ecological perspective based on bacterial community

From a radioecological perspective, increasing attention has been paid to the long-term stabilisation of decommissioned uranium mill tailings (UMT) repositories. However, little is known about the evaluation of decommissioning and remedial effects of UMT repositories from a microecological perspective based on bacterial communities. Here, we analysed the distribution and structure of soil community assemblies along different vertical soil profiles in a decommissioned UMT repository and explored the impact of soil properties, including physicochemical parameters, metal(loid)s, and radionuclides, on the bacterial assemblage. We found that the α diversity of the bacterial community was unaffected by variations in different soil profiles and taxa were classified at the phylum level with small significant differences. In contrast, the bacterial community structure in and around the UMT repository showed significant differences; however, this difference was significantly affected by soil metal(loid)s and physicochemical properties rather than soil radionuclides. In addition, seven bacterial genera with significant differences between the inner and surrounding regions of the repository could be used as potential indicators to further investigate the remedial effects on soil environmental quality. These findings provide novel insights into the construction of an assessment system and in situ biomonitoring of UMT repositories from a microecological perspective based on bacterial communities.

New insights into the effects of chlorpyrifos on soil microbes: Carbon and nitrogen cycle related microbes in wheat/maize rotation agricultural field

Chlorpyrifos, a broad-spectrum organophosphorus insecticide, has been widely detected worldwide and is a potential neurotoxin and endocrine disruptor. Besides, chlorpyrifos has been proven that have a negative effect on soil microbes. In the present study, chlorpyrifos formulation (LORSBAN®, 45% emulsifiable concentrate) was applied in an agricultural field at the recommended dose (R dose, 270.0 and 337.5 g a.i. ha^-1 for wheat and maize respectively) and double recommended (DR) dose. Chlorpyrifos residue level and effect on soil microbes related to soil carbon and nitrogen cycle function were analyzed. Results showed that the half-lives of chlorpyrifos in wheat and maize field soil were 7.23-8.23 and 1.45-1.77 d, respectively. Application of chlorpyrifos at even DR dose did not result in unacceptable residual chlorpyrifos, where the final residual chlorpyrifos in wheat/maize (leaf, stem, and grain) was meet the requirement of the maximum residual limit (0.5 mg kg^-1 for wheat and 0.05 mg kg^-1 for maize) in China. Chlorpyrifos enhanced the activity of β-glucosidase by increasing the relative abundance of Sphingosinicella and promoted the carbon cycle in wheat field. The changes of cbbLR and cbbLG gene abundance also confirmed that chlorpyrifos could affect the import and export of soil carbon pool. The effect of chlorpyrifos on soil N cycle was determined by changes in the abundance of the bacterial genus Gemmatimonas, which is associated with denitrification. Further analysis of N-cycle functional genes and urease activity showed that chlorpyrifos inhibited nitrogen fixation in wheat field, but promoted nitrogen fixation in maize field. In general, bacterial abundance, urease, and AOA-amoA gene could be early warning markers of chlorpyrifos contamination. The results demonstrated the negative effects of chlorpyrifos on soil microbes especially on soil C and N cycle in actual agricultural field. It provides new insights about chlorpyrifos environmental pollution and its effect on soil ecosystems.