Not merely noxious? Time-dependent hormesis and differential toxic effects systematically induced by rare earth elements in Escherichia coli

Enrichment of Terbium(III) under synergistic effect of biosorption and biomineralization by Bacillus sp. DW015 and Sporosarcina pasteurii

Biosorption and biomineralization are commonly used for the immobilization of metal ions. Biosorption is commonly used as a green method to enrich rare earth ions from wastewater. However, little attention has been paid to the facilitating role of biomineralization in the enrichment of rare earth ions. In this study, a strain of Bacillus sp. DW015, isolated from ion adsorption type rare earth ores and a urease-producing strain Sporosarcina pasteurii were used to enrich rare earth elements (REEs) from an aqueous solution. The results indicate that biomineralization accelerates the enrichment of Terbium(III) compared to biosorption alone. Kinetic analysis suggests that the main mode of action of DW015 was biosorption, following pseudo-second-order kinetics (R2 = 0.998). The biomineralization of DW015 did not significantly contribute to the enrichment of Tb(III), whereas excessive biomineralization of S. pasteurii led to a decrease in the enrichment of Tb(III). A synergistic system of biosorption and biomineralization was established by combining the two bacteria, with the optimal mixed bacteria (S. pasteurii:DW015) ratio being 1:19. This study provides fundamental support for the synergistic effect of biosorption and biomineralization and offers a new reference for future microbial-based enrichment methods.

IMPORTANCE

A weak microbially induced calcium carbonate precipitation (MICP) promotes the enrichment of Tb(III) by bacteria, while a strong MICP leads to the release of Tb(III). However, existing explanations cannot elucidate these mechanisms. In this study, the morphology of the bioprecipitation and the degree of Tb(III) enrichment were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The data revealed that MICP could drive stable attachment of Tb(III) onto the cell surface, forming a Tb-CaCO3 mixed solid phase. Excessive rapid rate of calcite generation could disrupt the Tb(III) adsorption equilibrium, leading to the release of Tb(III). Therefore, in order for Tb(III) to be stably embedded in calcite, it is necessary to have a sufficient number of adsorption sites on the bacteria and to regulate the rate of MICP. This study provides theoretical support for the process design of MICP for the enrichment of rare earth ions.

Drivers of rare earth elements (REEs) and radionuclides in changing subarctic (Nunavik, Canada) surface waters near a mining project

The emergence of mining projects for rare earth elements (REEs) in response to rising global demand and geopolitical factors introduces environmental concerns, such as the suspected release of anthropogenic REEs to aquatic systems and the coexistence of radionuclides (U, Th). Northern regions confront heightened challenges from limited research and accelerated climate change. Drivers of REEs in surface waters (including George and Koroc rivers, their tributaries, and thermokarst lakes) were studied (2017-2023) in subarctic Canada within a climate transition zone, near a prospective REE mine. Dissolved REEs (<0.45 μm) correlated positively with Al, Fe, Th, U, Cl- and DOC. A novel relationship with water temperature demonstrated an approximate 10-fold decrease in REE concentrations over the environmental gradient (2-20 ℃), suggesting complex implications for REE speciation under climate pressures. Optical analyses further predicted REEs were mobilized by humic-rich, terrestrial DOC, with correlations presenting a possible co-transport with Al, Fe and Th. Relationships for redox-sensitive Ce anomalies (Ce/Ce* = 0.18-1.2) with multi-valent trace metals (Al, Fe, Ti) and DOC were suggestive of a preferential adsorption of Ce by inorganic colloids in low-DOC systems. Findings emphasized the potential for changes in REE geochemistry with ongoing northern surface warming and vegetation shifts.

Survival, growth and digestive functions after exposure to nanodiamonds - Transgenerational effects beyond contact time in house cricket strains

The long-term exposure effects of nanodiamonds (NDs), spanning an organism's entire lifespan and continuing for subsequent generation, remain understudied. Most research has focused on evaluating their biological impacts on cell lines and selected organisms, typically over short exposure durations lasting hours or days. The study aimed to assess growth, mortality, and digestive functions in wild (H) and long-lived (D) strains of Acheta domesticus (Insecta: Orthoptera) after two-generational exposure to NDs in concentrations of 0.2 or 2 mg kg-1 of food, followed by their elimination in the third generation. NDs induced subtle stimulating effect that depended on the strain and generation. In the first generation, more such responses occurred in the H than in the D strain. In the first generation of H strain insects, contact with NDs increased survival, stimulated the growth of young larvae, and the activity of most digestive enzymes in mature adults. The same doses and exposure time did not cause similar effects in the D strain. In the first generation of D strain insects, survival and growth were unaffected by NDs, whereas, in the second generation, significant stimulation of those parameters was visible. Selection towards longevity appears to support higher resistance of the insects to exposure to additional stressor, at least in the first generation. The cessation of ND exposure in the third generation caused potentially harmful changes, which included, e.g., decreased survival probability in H strain insects, slowed growth of both strains, as well as changes in heterochromatin density and distribution in nuclei of the gut cells in both strains. Such a reaction may suggest the involvement of epigenetic inheritance mechanisms, which may become inadequate after the stress factor is removed.

Hormesis and Low Toxic Effects of Three Lanthanides in Microfungi Isolated from Rare Earth Mining Waste in Northwestern Russia

The low-dose toxicity of chloride and nitrate salts of three lanthanides (La, Ce and Nd) was tested on six microfungal species. Five of them (Geomyces vinaceus, Aspergillus niveoglaucus, Pseudogymnoascus pannorum, Penicillium simplicissimum and Umbelopsis isabellina) were isolated from the loparite ore tailings on the Kola Peninsula, northwestern Russia. Sydowia polyspora was a control strain. In the case of nitrate salts, the toxicity of REEs to four of six microorganisms was significantly (p < 0.5) lower compared to chloride salts. In this case, nitrates can play the role of exogenous nutrients, compensating for the toxic effect of REEs. Interestingly, U. isabellina only showed an opposite response, indicating the highest toxicity of nitrate (IC5 = 9-20 mg/L) REEs' salts compared to chlorides (IC5 = 80-195 mg/L) at low concentration levels. In addition, treatment with lanthanides showed a "hormesis effect" on fungal growth with stimulation at low doses and inhibition at high doses. However, U. isabellina and S. polyspora demonstrated the absence of hormetic response under the treatment of REEs' nitrate salt. Taking into account the specific hormetic responses and high tolerance of P. simplicissimum and U. isabellina to lanthanides, our findings may be useful in the assessment of the potential application of the selected fungi to bioremediation and REE bioleaching.

Genetic Modification of Acidithiobacillus ferrooxidans for Rare-Earth Element Recovery under Acidic Conditions

As global demands for rare-earth elements (REEs) continue to grow, the biological recovery of REEs has been explored as a promising strategy, driven by potential economic and environmental benefits. It is known that calcium-binding domains, including helix-loop-helix EF hands and repeats-in-toxin (RTX) domains, can bind lanthanide ions due to their similar ionic radii and coordination preference to calcium. Recently, the lanmodulin protein from Methylorubrum extorquens was reported, which has evolved a high affinity for lanthanide ions over calcium. Acidithiobacillus ferrooxidans is a chemolithoautotrophic acidophile, which has been explored for use in bioleaching for metal recovery. In this report, A. ferrooxidans was engineered for the recombinant intracellular expression of lanmodulin. In addition, an RTX domain from the adenylate cyclase protein of Bordetella pertussis, which has previously been shown to bind Tb3+, was expressed periplasmically via fusion with the endogenous rusticyanin protein. The binding of lanthanides (Tb3+, Pr3+, Nd3+, and La3+) was improved by up to 4-fold for cells expressing lanmodulin and 13-fold for cells expressing the RTX domains in both pure and mixed metal solutions. Interestingly, the presence of lanthanides in the growth media enhanced protein expression, likely by influencing protein stability. Both engineered cell lines exhibited higher recoveries and selectivities for four tested lanthanides (Tb3+, Pr3+, Nd3+, and La3+) over non-REEs (Fe2+ and Co2+) in a synthetic magnet leachate, demonstrating the potential of these new strains for future REE reclamation and recycling applications.

Metallophore Activity toward the Rare Earth Elements by Bacteria Isolated from Acid Mine Drainage Due to Coal Mining

The field of microbe-metal interactions has been gaining significant attention. While the direct impact of metal oxyanions on bacteria has been investigated, significantly less attention has been placed on the ability of certain microbes to 'collect' such metal ions via secreted proteins. Many bacteria possess low-weight molecules called siderophores, which collect Fe from the environment to be brought back to the cell. However, some appear to have additional roles, including binding other metals, termed 'metallophores'. Microbes can remove/sequester these from their surroundings, but the breadth of those that can be removed is still unknown. Using the Chromeazurol S assay, we identified eight isolates, most belonging to the genus Pseudomonas, possessing siderophore activity, mainly from sites impacted by coal mine drainage, also possessing a metallophore activity toward the rare earth elements that does not appear to be related to ionic radii or previously reported EC50 concentrations for E. coli. We found the strength of metallophore activity towards these elements was as follows: Pr > Sc > Eu > Tm > Tb > Er > Yb > Ce > Lu > Sm > Ho > La > Nd > Dy > Gd > Y. This is the first study to investigate such activity and indicates bacteria may provide a means of removal/recovery of these critical elements.

Effective assessment of lanthanide ion delivery into live cells by paramagnetic NMR spectroscopy

We report an effective assessment of lanthanide ion (Ln3+) delivery into live cells by paramagnetic NMR spectroscopy. Free Ln3+ ions are toxic to live cells resulting in a gradual leakage of target proteins to the extracellular media. The citrate-Ln3+ complex is an efficient and mild reagent over the free Ln3+ form for live cell delivery.

Rare earth element bioaccumulation and cerium anomalies in biota from the Eastern Canadian subarctic (Nunavik)

Recent increases in the demand for rare earth elements (REE) have contributed to various countries' interest in exploration of their REE deposits, including within Canada. Current limited knowledge of REE distribution in undisturbed subarctic environments and their bioaccumulation within northern species is addressed through a collaborative community-based environmental monitoring program in Nunavik (Quebec, Canada). This study provides background REE values (lanthanides + yttrium) and investigates REE anomalies (i.e., deviations from standard pattern) across terrestrial, freshwater, and marine ecosystems in an area where a REE mining project is in development. Results are characteristic of a biodilution of REE, with the highest mean total REE concentrations (ΣREE) reported in sediments (10² nmol/g) and low trophic level organisms (i.e., biofilm, macroalgae, macroinvertebrates, common mussels, and reindeer lichens; 10¹-10² nmol/g), and the lowest mean concentrations in higher-level consumers (i.e., goose, ptarmigan, char, whitefish, cod, sculpin and seal; 10^-2 - 10¹ nmol/g). The animal tissues are of importance to northern villages and analyses demonstrate a species-specific bioaccumulation of REE, with mean concentrations up to 40 times greater in liver compared to muscle, with bones and kidneys presenting intermediate concentrations and the lowest in blubber. Further, a tissue-specific fractionation was presented, with significant light REE (LREE) enrichment compared to heavy REE (HREE) in consumer livers (LREE/HREE ≅ 10¹) and the most pronounced negative cerium (Ce) anomalies (<0.80) in liver and bones of fish species. These fractionation patterns, along with novel negative relationships presented between fish size (length, mass) and Ce anomalies suggest metabolic, ecological, and/or environmental influences on REE bioaccumulation and distribution within biota. Background concentration data will be useful in the establishment of REE guidelines; and the trends discussed support the use of Ce anomalies as biomarkers for REE processing in animal species, which requires further investigation to better understand their controlling factors.

Evaluation of Rare Earth Element-Associated Hormetic Effects in Candidate Fertilizers and Livestock Feed Additives

Rare earth elements (REEs) are recognized as emerging contaminants with implications in human and environmental health. Apart from their adverse effects, REEs have been reported as having positive effects when amended to fertilizers and livestock feed additives, thus suggesting a hormetic trend, implying a concentration-related shift from stimulation to inhibition and toxicity, with analogous trends that have been assessed for a number of xenobiotics. In view of optimizing the success of REE mixtures in stimulating crop yield and/or livestock growth or egg production, one should foresee the comparative concentration-related effects of individual REEs (e.g., Ce and La) vs. their mixtures, which may display distinct trends. The results might prompt further explorations on the use of REE mixtures vs. single REEs aimed at optimizing the preparation of fertilizers and feed additives, in view of the potential recognition of their use in agronomy and zootechny.

Hormetic Effects of Cerium, Lanthanum and Their Combination at Sub-micromolar Concentrations in Sea Urchin Sperm

Rare earth elements (REEs) cerium (Ce) and lanthanum (La) and their combination were tested across a concentration range, from toxic (10^-4 to 10^-5 M) to lower concentrations (10^-6 to 10^-8 M) for their effects on sea urchin (Sphaerechinus granularis) sperm. A significantly decreased fertilization rate (FR) was found for sperm exposed to 10^-5 M Ce, La and their combination, opposed to a significant increase of FR following 10^-7 and 10^-8 M REE sperm exposure. The offspring of REE-exposed sperm showed significantly increased developmental defects following sperm exposure to 10^-5 M REEs vs. untreated controls, while exposure to 10^-7 and 10^-8 M REEs resulted in significantly decreased rates of developmental defects. Both of observed effects-on sperm fertilization success and on offspring quality-were closely exerted by Ce or La or their combination.

Locked up Inside the Vessels: Rare Earth Elements Are Transferred and Stored in the Conductive Tissues of the Accumulating Fern Dryopteris erythrosora

Rare earth elements (REEs) are strategic metals strongly involved in low-carbon energy conversion. However, these emerging contaminants are increasingly disseminated into ecosystems, raising concern regarding their toxicity. REE-accumulating plants are crucial subjects to better understand REE transfer to the trophic chain but are also promising phytoremediation tools. In this analysis, we deciphered REE accumulation sites in the REE-accumulating fern Dryopteris erythrosora by synchrotron X-ray μfluorescence (μXRF). This technique allows a high-resolution and in situ analysis of fresh samples or frozen-hydrated cross sections of different organs of the plant. In the sporophyte, REEs were translocated from the roots to the fronds by the xylem sap and were stored within the xylem conductive system. The comparison of REE distribution and accumulation levels in the healthy and necrotic parts of the frond shed light on the differential mobility between light and heavy REEs. Furthermore, the comparison emphasized that necrotized areas were not the main REE-accumulating sites. Finally, the absence of cell-to-cell mobility of REEs in the gametophyte suggested the absence of REE-compatible transporters in photosynthetic tissues. These results provide valuable knowledge on the physiology of REE-accumulating ferns to understand the REE cycle in biological systems and the expansion of phytotechnologies for REE-enriched or REE-contaminated soils.

From geochemistry to ecotoxicology of rare earth elements in aquatic environments: Diversity and uses of normalization reference materials and anomaly calculation methods

The geochemistry of rare earth elements (REEs) has been studied for a long time and has allowed us to highlight enrichments or depletions of REEs in aquatic ecosystems and to estimate anthropogenic inputs through normalization of data to different reference materials. This review of current literature on REE normalization highlighted the large number of different reference materials (a total of 12), as well as different anomaly calculation methods. This statement showed a real need for method harmonization to simplify the comparison between studies, which is currently very difficult. Normalization to Post-Archean Australian Shale (PAAS) emerged as being the most used (33 % of reported studies) regardless of the location and the nature of the studied samples and seem to be of higher quality. The interest of other reference materials was nevertheless underlined, as they could better represent the geographical situation or the nature of samples. Two main anomaly calculation methods have been highlighted: the linear interpolation/extrapolation and the geometric extrapolation using logarithmic modeling. However, due to variations in the estimation of neighbors' values, these two methods produce many different equations for the anomaly calculation of a single element. Current normalization practices based on shales and chondrites are suitable for abiotic samples but are questionable for biota. Indeed, normalization is increasingly used in studies addressing ecotoxicological issues which focus on biota and often aim to estimate the anthropogenic origin of bioaccumulated REEs. Due to the interspecific variability, as well as the complexity of mechanisms occurring in organisms when exposed to contaminants, new reference materials need to be established to consider the bioaccumulation/metabolization processes and the anthropogenic inputs of REEs based on the results of biotic samples.

Scandium-microorganism interactions in new biotechnologies

Scandium (Sc) plays a special role in high-tech industries because of its wide application in green, space, and defense technologies. However, Sc mining and purification are problematic due to political, technological, and environmental difficulties. The deficit of this element limits global technological development. One sustainable solution to this problem is to use microorganisms to extract Sc from ore and waste, as well as to concentrate and separate it from other elements. Sc also demonstrates attractive metabolic effects on microbes that is of great interest in white biotechnology. Sc increases the production of proteins and secondary metabolites and activates poorly expressed genes. This review offers a comprehensive analysis of current knowledge on the application of Sc-microorganism interactions in promising biotechnologies, its perspectives, and future challenges.

Combined omics approaches reveal distinct responses between light and heavy rare earth elements in Saccharomyces cerevisiae

The rapid development of green energy sources and new medical technologies contributes to the increased exploitation of rare earth elements (REEs). They can be subdivided into light (LREEs) and heavy (HREEs) REEs. Mining, industrial processing, and end-use practices of REEs has led to elevated environmental concentrations and raises concerns about their toxicity to organisms and their impact on ecosystems. REE toxicity has been reported, but its precise underlying molecular effects have not been well described. Here, transcriptomic and proteomic approaches were combined to decipher the molecular responses of the model organism Saccharomyces cerevisiae to La (LREE) and Yb (HREE). Differences were observed between the early and late responses to La and Yb. Several crucial pathways were modulated in response to both REEs, such as oxidative-reduction processes, DNA replication, and carbohydrate metabolism. REE-specific responses involving the cell wall and pheromone signalling pathways were identified, and these responses have not been reported for other metals. REE exposure also modified the expression and abundance of several ion transport systems, with strong discrepancies between La and Yb. These findings are valuable for prioritizing key genes and proteins involved in La and Yb detoxification mechanisms that deserve further characterization to better understand REE environmental and human health toxicity.

A novel biotechnology based on periphytic biofilms with N-acyl-homoserine-lactones stimulation and lanthanum loading for phosphorus recovery

This study presents an approach for developing periphytic biofilm with N-acyl-homoserine-lactones (AHLs) stimulation and lanthanum (La, a rare earth element) loading, to achieve highly efficient and stable phosphorus (P) recovery from wastewater. AHLs stimulated biofilm growth and formation, also improved stable P entrapment by enhancing extracellular polymeric substance (EPS) production and optimizing P-entrapment bacterial communities. Periphytic biofilms loading La is based on ligand exchanges, and La loading achieved initial rapid P entrapment by surface adsorption. The combination of AHLs stimulation and La loading achieved 99.0% P entrapment. Interestingly, the enhanced EPS production stimulated by AHLs protected biofilms against La. Moreover, a method for P and La separately recovery from biofilms was developed, achieving 89-96% of P and 88-93% of La recovery. This study offers a promising biotechnology to reuse La from La-rich wastewater and recover P by biofilm doped with La, which results in a win-win situation for resource sustainability.

Spatial distribution of multielements including lanthanides in sediments of Iron Gate I Reservoir in the Danube River

Recent studies show that lanthanides (Ln) are becoming emerging pollutants due to their wide application in new technologies, but their environmental fate, transport, and possible accumulation are still relatively unknown. This study aims to determine major and trace elements including Ln in the Danube River sediment which either belong or close to the Iron Gate Reservoir. The Iron Gate Reservoir is characterized by accumulation of sediments as an effect of building hydropower dam Iron Gate I. The surface sediments were collected on the Danube River-1141 to 864 km and three tributaries along this waterway. Two samples of deep sediments were used for comparison. The results indicate the significant upward enrichment of Zn, Sb, Cr, Nd, and Dy in sediments belongs to the Iron Gate Reservoir. The sample 4-Smed is labelled as a hot spot of contamination with Zn, Cr, As, Sb, Nd, and Dy. Also, a trend of increasing concentration in the time period from 1995 to 2016 was found for elements Zn, Cr, and Ni in sediment samples in the Iron Gate Reservoir. Chemometric analysis shows the grouping of sample sites into clusters characterized by the following properties: (i) increased concentration of all measured elements (samples within the Iron Gate Reservoir); (ii) increased Cu concentration (11-Pek); and (iii) lower concentrations of the measured elements (deep sediments). The data presented hereby contribute to the monitoring of pollution of the River Danube sediments and give the first view of Ln profile in the studied sediments.

Impacts of anthropogenic gadolinium on the activity of the ammonia oxidizing bacterium Nitrosomonas europaea

Widespread use of gadolinium-based contrast agents in medical imaging has resulted in increased Gd inputs to municipal wastewater treatment plants. Others have reported that typical wastewater treatment does not attenuate Gd, resulting in discharges to natural waters. However, whether elevated Gd impacts the performance of biological treatment has not been investigated. We examined whether gadolinium chloride or Gd chelated with diethylenetriaminepentaacetic acid (DTPA) affected the activity of the model nitrifying bacterium Nitrosomonas europaea. At nominal GdCl₃ additions ranging from 1 to 500 μM, no impact was observed compared to the control. Most (>98%) of the added Gd precipitated, and extracellular GdPO₄ nanoparticles were observed. When chelated with DTPA, Gd remained soluble, but no statistically significant impact on ammonia oxidation was observed until the highest concentrations tested. At 300 and 500 μM Gd-DTPA, a temporary reduction of nitrite production relative to the control (effect size 1.3 mg l^-1 and 1.5 mg l^-1, respectively, at 24 h) was seen. By itself, DTPA was highly inhibitory. Modeling suggested that DTPA likely chelated other metals, but adjusting the concentrations of the most abundant metals in the medium, calcium and magnesium, indicated that lowering their free ion activities was probably not the cause of inhibition. Complexation of other essential metals was more likely. Our studies indicate that while the low bioavailability of Gd may limit its ecosystem impacts, the role of synthetic ligands used with Gd and other rare earth elements should be considered as the production, use and disposal of these elements increases.