Bioremediation Of Radionuclides Research Articles

Radiotolerant endophytic bacteria and analysis of the effects of 137Cesium on the metabolome of Pantoea sp.

Some bacteria have developed mechanisms to withstand the stress caused by ionizing radiation. The ability of these radioresistant microorganisms to survive high levels of radiation is primarily attributed to their DNA repair mechanisms and the production of protective metabolites. To determine the effect of irradiation on bacterial growth, we propose to compare the metabolites produced by the irradiated isolates to those of the control (non-irradiated isolates) using mass spectrometry, molecular networking, and chemometric analysis. We identified the secondary metabolites produced by these bacteria and observed variations in growth following irradiation. Notably, after 48h of exposure to radiation, Pantoea sp. bacterial cells exhibited a significant 6-log increase compared to non-irradiated cells. Non-irradiated cells produce exclusively Pyridindolol, 1-hydroxy-4-methylcarbostyril, N-alkyl, and N-2-alkoxyethyl diethanolamine, while 5'-methylthioadenosine was detected only in irradiated cells. These findings suggest that the metabolic profile of Pantoea sp. remained relatively stable. The results obtained from this study have the potential to facilitate the development of innovative strategies for harnessing the capabilities of endophytic bacteria in radiological protection and bioremediation of radionuclides.

Marine halophilic archaeal isolate Halococcus sp. with emphasis on bioremediation of radionuclides through extracellular biomolecules

AbstractBACKGROUNDMarine archaea have gained special attention for their unique ability to survive in extreme salt concentrations. Some archaeal isolates have been found to thrive in the presence of radioactive contaminants. In this study, Halococcus sp. ENMS8 has been isolated from marine sediment sample with special emphasis on bioremediation of radionuclide cesium.RESULTSHalococcus sp. ENMS8 has the ability to remove 76.46% of cesium ions noted at a concentration of 100 mmol L−1 followed by 60.5%, 52.16% and 42.9% of cesium ion adsorption at concentrations of 150, 200 and 250 mmol L−1 Cs+, respectively. The minimal level of 4.43% of cesium adsorption was noted at 500 mmol L−1 concentration in the presence of 106 archaeal cells per milliliter. Similarly, adsorption of cesium (500 mmol L−1) at various concentrations of archaeal extracellular polymeric substances (EPS) has been shown to be 76.4% of Cs+ adsorption at 1 g L−1. The composition of extracted EPS from ENMS8 in the presence of CsCl and control has been estimated. Cesium adsorption was further confirmed with Fourier transform infrared spectroscopy, and scanning electron microscopy was used to obtain high‐resolution images of the surface topology of Halococcus sp. ENMS8 EPS in the presence of cesium. The crystallographic structure and properties of cesium were studied by energy‐dispersive X‐ray spectroscopy.CONCLUSIONThe present study concluded that Halococcus sp. ENMS8 can immobilize cesium through EPS in an eco‐friendly approach. © 2023 Society of Chemical Industry (SCI).

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.

Microbially mediated kinetic sulfur isotope fractionation: reactive transport modeling benchmark

Microbially mediated sulfate reduction is a ubiquitous process in many subsurface systems. Isotopic fractionation is characteristic of this anaerobic process, since sulfate-reducing bacteria (SRB) favor the reduction of the lighter sulfate isotopologue (S32O42−) over the heavier isotopologue (S34O42−). Detection of isotopic shifts has been utilized as a proxy for the onset of sulfate reduction in subsurface systems such as oil reservoirs and aquifers undergoing heavy metal and radionuclide bioremediation. Reactive transport modeling (RTM) of kinetic sulfur isotope fractionation has been applied to field and laboratory studies. We developed a benchmark problem set for the simulation of kinetic sulfur isotope fractionation during microbially mediated sulfate reduction. The benchmark problem set is comprised of three problem levels and is based on a large-scale laboratory column experimental study of organic carbon amended sulfate reduction in soils from a uranium-contaminated aquifer. Pertinent processes impacting sulfur isotopic composition such as microbial sulfate reduction and iron-sulfide reactions are included in the problem set. This benchmark also explores the different mathematical formulations in the representation of kinetic sulfur isotope fractionation as employed in the different RTMs. Participating RTM codes are the following: CrunchTope, TOUGHREACT, PHREEQC, and PHT3D. Across all problem levels, simulation results from all RTMs demonstrate reasonable agreement.

Bioremediation of Sr2+ ion radionuclide by using marine Streptomyces sp. CuOff24 extracellular polymeric substances

AbstractBACKGROUNDMicrobial biosorption is recognized as a resourceful process for the remediation of pollution from contaminated environs. To investigate radionuclide bioremediation, carbohydrate contained extracellular polymeric substance (EPS) and strontium ion (Sr+) tolerant marine actinobacterium has been isolated and identified as Streptomyces sp. CuOff24 through 16S rDNA sequencing.RESULTSEPS was extracted, characterized and the biosorption of the long half‐life radionuclide of Sr2+ was also performed. EPS could remove 82% of Sr2+ from the experimental solution of 100 mg L−1 of strontium chloride (SrCl2). Furthermore, EPS composition also obtained with the presence of Sr2+ radionuclide and major contents of carbohydrate (68.6%) followed by protein (12.3%), nucleic acid (10.4%) and unidentified compounds 8.7%) were quantified. The spectroscopy study also confirmed the presence of carbohydrate functional groups presence in the EPS surface were probably to be involved in Sr2+ adsorption.CONCLUSIONOverall results conclude that, marine actinobacterial EPS could be used for the large‐scale remediation of radionuclides contaminated environment. © 2019 Society of Chemical Industry

Extremophilic Microfactories: Applications in Metal and Radionuclide Bioremediation.

Metals and radionuclides (M&Rs) are a worldwide concern claiming for resilient, efficient, and sustainable clean-up measures aligned with environmental protection goals and global change constraints. The unique defense mechanisms of extremophilic bacteria and archaea have been proving usefulness towards M&Rs bioremediation. Hence, extremophiles can be viewed as microfactories capable of providing specific and controlled services (i.e., genetic/metabolic mechanisms) and/or products (e.g., biomolecules) for that purpose. However, the natural physiological plasticity of such extremophilic microfactories can be further explored to nourish different hallmarks of M&R bioremediation, which are scantly approached in the literature and were never integrated. Therefore, this review not only briefly describes major valuable extremophilic pathways for M&R bioremediation, as it highlights the advances, challenges and gaps from the interplay of ‘omics’ and biological engineering to improve extremophilic microfactories performance for M&R clean-up. Microfactories’ potentialities are also envisaged to close the M&R bioremediation processes and shift the classical idea of never ‘getting rid’ of M&Rs into making them ‘the belle of the ball’ through bio-recycling and bio-recovering techniques.

Quantitative Modeling of Microbial Population Responses to Chronic Irradiation Combined with Other Stressors.

Microbial population responses to combined effects of chronic irradiation and other stressors (chemical contaminants, other sub-optimal conditions) are important for ecosystem functioning and bioremediation in radionuclide-contaminated areas. Quantitative mathematical modeling can improve our understanding of these phenomena. To identify general patterns of microbial responses to multiple stressors in radioactive environments, we analyzed three data sets on: (1) bacteria isolated from soil contaminated by nuclear waste at the Hanford site (USA); (2) fungi isolated from the Chernobyl nuclear-power plant (Ukraine) buildings after the accident; (3) yeast subjected to continuous γ-irradiation in the laboratory, where radiation dose rate and cell removal rate were independently varied. We applied generalized linear mixed-effects models to describe the first two data sets, whereas the third data set was amenable to mechanistic modeling using differential equations. Machine learning and information-theoretic approaches were used to select the best-supported formalism(s) among biologically-plausible alternatives. Our analysis suggests the following: (1) Both radionuclides and co-occurring chemical contaminants (e.g. NO2) are important for explaining microbial responses to radioactive contamination. (2) Radionuclides may produce non-monotonic dose responses: stimulation of microbial growth at low concentrations vs. inhibition at higher ones. (3) The extinction-defining critical radiation dose rate is dramatically lowered by additional stressors. (4) Reproduction suppression by radiation can be more important for determining the critical dose rate, than radiation-induced cell mortality. In conclusion, the modeling approaches used here on three diverse data sets provide insight into explaining and predicting multi-stressor effects on microbial communities: (1) the most severe effects (e.g. extinction) on microbial populations may occur when unfavorable environmental conditions (e.g. fluctuations of temperature and/or nutrient levels) coincide with radioactive contamination; (2) an organism’s radioresistance and bioremediation efficiency in rich laboratory media may be insufficient to carry out radionuclide bioremediation in the field—robustness against multiple stressors is needed.

Isolation and characterization of a radiation-resistant bacterium from Taklamakan Desert showing potent ability to accumulate Lead (II) and considerable potential for bioremediation of radioactive wastes.

Radioactive wastes always contain radioactive substances and a lot of Pb compound and other heavy metals, which severely contaminate soils and groundwater. Thus, search for radiation-resistant microorganisms that are capable of sequestering Pb contaminants from the contaminated sites is urgently needed. However, very few such microorganisms have been found so far. In the present study, we discovered a novel Gram-negative bacterium from the arid Taklamakan desert, which can strongly resist both radiation and Pb(2+). Phylogenetic and phenotypic analysis indicated that this bacterial strain is closely affiliated with Microvirga aerilata, and was thus referred to as Microvirga aerilata LM (=CCTCC AB 208311). We found that M. aerilata LM can effectively accumulate Pb and form intracellular precipitations. It also keeps similar ability to remove Pb(2+) under radioactive stress. Our data suggest that M. aerilata LM may offer an effective and eco-friendly in situ approach to remove soluble Pb contaminants from radioactive wastes.

Electron flow in acidic subsurface sediments co-contaminated with nitrate and uranium

The combination of low pH and high concentrations of nitrate and radionuclides in the subsurface is representative of many sites within the U.S. nuclear weapons complex managed by the Department of Energy (DOE), including the DOE’s Environmental Remediation Sciences Program Field Research Center (ORFRC), in Oak Ridge, Tennessee. In order to provide a further understanding of the coupled microbiological and geochemical processes limiting radionuclide bioremediation, we determined the rates and pathways of terminal-electron accepting processes (TEAPs) in microcosm experiments using close to in situ conditions with ORFRC subsurface materials. At the in situ pH range of 4–5, carbon substrate utilization and TEAP rates were diminished, such that nitrate was not depleted and metal reduction was prevented. Upon biostimulation by pH neutralization and carbon substrate addition, TEAPs were stimulated to rates that rival those measured in organic-rich surficial sediments of aquatic environments, and extremely high nitrate concentrations (0.4–0.5 M) were not found to be toxic to microbial metabolism. Metal reduction under neutral pH conditions started once nitrate was depleted to low levels in response to biostimulation. Acidity controlled not only the rates but also the pathways of microbial activity. Denitrification predominated in sediments originating from neutral pH zones, while dissimilatory nitrate reduction to ammonium occurred in neutralized acidic microcosms amended with glucose. Electron donors were determined to stimulate microbial metabolism leading to metal reduction in the following order: glucose > ethanol > lactate > hydrogen. In microcosms of neutralized acidic sediments, 80–90% of C equivalents were recovered as fermentation products, mainly as acetate. Due to the stress imposed by low pH on microbial metabolism, our results indicate that the TEAPs of acidic subsurface sediment are inherently different from those of neutral pH environments and neutralization will be necessary to achieve sufficient metabolic rates for radionuclide remediation.

Actinide and metal toxicity to prospective bioremediation bacteria

Bacteria may be beneficial for alleviating actinide contaminant migration through processes such as bioaccumulation or metal reduction. However, sites with radioactive contamination often contain multiple additional contaminants, including metals and organic chelators. Bacteria-based bioremediation requires that the microorganism functions in the presence of the target contaminant, as well as other contaminants. Here, we evaluate the toxicity of actinides, metals and chelators to two different bacteria proposed for use in radionuclide bioremediation, Deinococcus radiodurans and Pseudomonas putida, and the toxicity of Pu(VI) to Shewanella putrefaciens. Growth of D. radiodurans was inhibited at metal concentrations ranging from 1.8 microM Cd(II) to 32 mM Fe(III). Growth of P. putida was inhibited at metal concentrations ranging from 50 microM Ni(II) to 240 mM Fe(III). Actinides inhibited growth at mM concentrations: chelated Pu(IV), U(VI) and Np(V) inhibit D. radiodurans growth at 5.2, 2.5 and 2.1 mM respectively. Chelated U(VI) inhibits P. putida growth at 1.7 mM, while 3.6 mM chelated Pu(IV) inhibits growth only slightly. Pu(VI) inhibits S. putrefaciens growth at 6 mM. These results indicate that actinide toxicity is primarily chemical (not radiological), and that radiation resistance does not ensure radionuclide tolerance. This study also shows that Pu is less toxic than U and that actinides are less toxic than other types of metals, which suggests that actinide toxicity will not impede bioremediation using naturally occurring bacteria.