Low Concentrations of Silver Nanoparticles and Silver Ions Perturb the Antioxidant Defense System and Nitrogen Metabolism in N2-Fixing Cyanobacteria

Molecular disruptions in microalgae caused by Acidithiobacillus ferrooxidans: Photosynthesis, oxidative stress, and energy metabolism in acid mine drainage

Microalgae are recognized for their potential in the bioremediation of acid mine drainage (AMD), despite the challenges posed by AMD's low pH, high heavy metal content, and oligotrophic conditions. However, the impact of AMD chemoautotrophic microorganisms on microalgal growth and remediation efforts within AMD has been largely overlooked. This study aims to elucidate the effects the chemoautotrophic microorganism, Acidithiobacillus ferrooxidans, on the growth activity and metabolism of acid-tolerant microalgae, and to explore the molecular mechanisms of microalgal response. Our findings reveal that the presence of A. ferrooxidans inhibits the growth and alkaline production of Parachlorella sp. MP1, resulting in a 90.86 % reduction in biomass. Physiological, biochemical, and transcriptomic studies, indicate that oxidative stress, photosynthesis, and energy metabolism are the metabolic processes most affected by A. ferrooxidans. Specifically, A. ferrooxidans introduces an increased production of reactive oxygen species (ROS) in Parachlorella sp. MP1, leading to an upregulation of genes and enzymes associated with peroxisome activity and intensifying oxidative stress within the cells. Downregulation of photosynthesis-related genes disrupts the electron transport chain, inhibiting photosynthesis. Furthermore, alterations in the gene expression of pyruvate and acetyl-CoA metabolic pathways result in energetic pathway disruption. These insights contribute to a better understanding of how A. ferrooxidans influence the growth metabolism of acid-tolerant microalgae in AMD environments and inform the optimization of microalgal application strategies in AMD bioremediation engineering.

Silver nanoparticles alter planktonic community structure and promote ecosystem respiration in freshwater mesocosms

The widespread use of silver nanoparticles (AgNPs) has resulted in their release into the aquatic environment, which threatens the health of aquatic ecosystems. Although the ecotoxicological effects of AgNPs have been widely reported at individual and population levels, the impact of long-term exposure to AgNPs on community structure and ecosystem function in aquatic ecosystems remains poorly understood. Herein, the present study investigated the effects of long-term exposure (28 d) to environmentally relevant concentrations (1 μg/L and 10 μg/L) of AgNPs on the community structure and function of freshwater ecosystems by artificially constructed 28 mesocosms freshwater ecosystem in experimental greenhouses, using plastic water tanks and food web manipulation. The results showed that long-term exposure to AgNPs significantly altered the community structure of zooplankton, phytoplankton, and bacterioplankton in the aquatic ecosystem. Exposure to 10 μg/L AgNPs significantly reduced the zooplankton density (70.3%, p < 0.05) and increased the phytoplankton biomass and bacterial richness and diversity via a "top-down effect." With regards to ecosystem function, AgNPs exposure significantly increased the respiration in freshwater ecosystems but did not have a significant effect on decomposition. The partial least squares path modeling (PLS-PM) further revealed that AgNPs may have a negative impact on ecosystem functions by reducing zooplankton community density and thus increasing phytoplankton biomass. This study is the first to show that long-term exposure to environmentally relevant concentrations of AgNPs leads to alterations in plankton community structure and promotes respiration in freshwater ecosystems. It emphasizes the need for assessing the environmental risk of long-term exposure to AgNPs at the ecosystem level.

Low-frequency ultrasound assisted contact-electro-catalysis for efficient inactivation of Microcystis aeruginosa

Frequent cyanobacterial blooms pose a serious threat to the aquatic ecosystem and human health, so developing an efficient algae removal method is a long-term goal for bloom management. Current technologies for algal bloom control need urgent improvement in terms of algicide recovery, eco-friendliness and cost. Here we propose a contact-electro-catalytic method, using polytetrafluoroethylene (PTFE) film as a reusable catalyst. This contact-electro-catalytic approach involves the generation of reactive oxygen species (e.g., O2•-, HO•, 1O2 and H2O2) through water-PTFE contact electrification under the low-frequency ultrasonic waves, facilitating the inactivation of algae. The removal rate of the cyanobacterium Microcystis aeruginosa (M. aeruginosa) exposured to the water-PTFE contact-electro-catalytic system is almost five times greater than that of ultrasound alone after 5 h. A mechanistic investigation revealed that the contact-electro-catalytic system damaged the photosynthetic activity, antioxidant system and membrane integrity of the cells. Additionally, LC-MS metabolomic analysis indicated that this system caused substantial significant disruptions in the TCA cycle, amino acid metabolism, purine metabolism and phospholipid metabolism. Three-dimensional fluorescence spectroscopy suggested contact-electro-catalysis could further availably degrade the organic matter. We anticipate that this method can provide an eco-friendly, highly efficient and economic approach for effective control of harmful algal blooms.

Toxic effect of mussel Mytilus galloprovincialis exposed to Ag-TiO2 and ZnTi2O4-TiO2 bicomponent nanoparticles

Nanoparticles (NPs) are widely used in various fields, including antifouling paints for ships and industrial structures submerged in water. The potential impact of NPs on aquatic organisms, particularly their potential toxicity, is a significant concern, as their negative impact has been relatively poorly studied. In this study, we evaluated the effect of different concentrations of bimetallic Ag-TiO₂ and ZnTi₂O₄-TiO₂ NPs, which could potentially be used in antifouling coatings, on the hemocytes of the Mediterranean mussel Mytilus galloprovincialis. Hemocytes were exposed to NPs at concentrations of 0.1-1 mg/L for 1 and 2 h, and the production of reactive oxygen species (ROS), levels of DNA damage, and number of dead cells were measured. Exposure to Ag-TiO₂ NPs at 1 mg/L concentration for 1 h suppressed ROS production in hemocytes and reduced the relative number of agranulocytes in cell suspensions, without inducing DNA damage or cell death. Exposure to ZnTi2O4-TiO2 NPs did not cause changes in the ratio of granulocytes to agranulocytes in suspensions, nor did it affect other functional parameters of hemocytes. However, after a 2 h exposure period, ZnTi2O4-TiO2 NPs (1 mg/L) significantly reduced the production of ROS by hemocytes. These findings suggest that Ag-TiO2 and ZnTi2O4-TiO2 NPs have low acute toxicity for marine bivalves.

Toxicity of Moxifloxacin on the Growth, Photosynthesis, Antioxidant System, and Metabolism of Microcystis aeruginosa at Different Phosphorus Levels

Moxifloxacin (MOX), a widely used novel antibiotic, may pose ecological risks at its actual environmental concentrations, as has been detected in aquatic systems. However, its ecotoxicity to aquatic organisms and regulatory mechanisms of phosphorus in eutrophic aqueous environments are still limited. This study aimed to analyze its physiological and biochemical parameters, including cellular growth, chlorophyll fluorescence, photosynthetic pigments, oxidative stress biomarkers, and metabolomics to elucidate the toxicity induced by environmental concentrations of MOX in Microcystis aeruginosa at different phosphorus levels. The results revealed that the EC50 values of MOX on M. aeruginosa at different phosphorus concentrations were 8.03, 7.84, and 6.91 μg/L, respectively, indicating MOX toxicity was exacerbated with increasing phosphorus levels. High phosphorus intensified the suppression of chlorophyll fluorescence and photosynthetic pigments, while activating the antioxidant enzyme, indicating severe peroxidation damage. Metabolomic analysis showed MOX induced different discriminating metabolites under different phosphorus levels, and perturbed more biological pathways at higher phosphorus concentrations, such as starch and sucrose metabolism, pyrimidine metabolism, and glycerolipid metabolism. This indicates that phosphorus plays an important role in regulating metabolism in M. aeruginosa exposed to MOX. The findings provide valuable information on the mechanisms involved in cyanobacteria responses to antibiotic stress, and offer a theoretical basis for accurately assessing antibiotic toxicity in eutrophic aqueous environments.

Mass Spectrometry Imaging Reveals the Morphology-Dependent Toxicological Effects of Nanosilvers on Multiple Organs of Adult Zebrafish (Danio rerio)

Nanosilvers with multifarious morphologies have been extensively used in many fields, but their morphology-dependent toxicity toward nontarget aquatic organisms remains largely unclear. Herein, we used matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) to investigate the toxicological effects of silver nanomaterials with various morphologies on spatially resolved lipid profiles within multiple organs in adult zebrafish, especially for the gill, liver, and intestine. Integrated with histopathology, enzyme activity, accumulated Ag contents and amounts, as well as MSI results, we found that nanosilvers exhibit morphology-dependent nanotoxicity by disrupting lipid levels and producing oxidative stress. Silver nanospheres (AgNSs) had the highest toxicity toward adult zebrafish, whereas silver nanoflakes (AgNFs) exhibited greater toxicity than silver nanowires (AgNWs). Levels of differential phospholipids, such as PC, PE, PI, and PS, were associated with nanosilver morphology. Notably, we found that AgNSs induced greater toxicity in multiple organs, such as the brain, gill, and liver, while AgNWs and AgNFs caused greater toxicity in the intestine than AgNSs. Lipid functional disturbance and oxidative stress further caused inflammation and membrane damage after exposure to nanosilvers, especially with respect to sphere morphology. Taken together, these findings will contribute to clarifying the toxicological effects and mechanisms of different morphologies of nanosilvers in adult zebrafish.

Molecular mechanism of dissolvable metal nanoparticles-enhanced CO2 fixation by algae: Metal-chlorophyll synthesis

Algae-driven photosynthetic CO2 fixation is a promising strategy to mitigate global climate changes and energy crises. Yet, the presence of metal nanoparticles (NPs), particularly dissolvable NPs, in aquatic ecosystems introduces new complexities due to their tendency to release metal ions that may perturb metabolic processes related to algal CO2 fixation. This study selected six representative metal NPs (Fe3O4, ZnO, CuO, NiO, MgO, and Ag) to investigate their impacts on CO2 fixation by algae (Chlorella vulgaris). We discovered an intriguing phenomenon that bivalent metal ions released from the metal NPs, especially from ZnO NPs, substituted Mg2+ within the porphyrin ring. This interaction led to 81.8% and 76.1% increases in Zinc-chlorophyll and Magnesium-chlorophyll contents within algal cells at 0.01 mM ZnO NPs, respectively. Integrating metabolomics and transcriptomics analyses revealed that ZnO NPs mainly promoted the photosynthesis-antenna protein pathway, porphyrin and chlorophyll metabolism, and carbon fixation pathway, thereby mitigating the adverse effects of Zn2+ substitution in light harvesting and energy transfer for CO2 fixation. Ultimately, the genes encoding Rubisco large subunit (rbcL) responsible for CO2 fixation were upregulated to 2.60-fold, resulting in a 76.3% increase in carbon fixation capacity. Similar upregulations of rbcL expression (1.13-fold) and carbon fixation capacity (76.1%) were observed in algal cells even at 0.001 mM ZnO NPs, accompanied by valuable lipid accumulation. This study offers novel insights into the molecular mechanism underlying NPs on CO2 fixation by algae and potentially introduces strategies for global carbon sequestration.

The secondary outbreak risk and mechanisms of Microcystis aeruginosa after H2O2 treatment

The secondary outbreak of cyanobacteria after algicide treatment has been a serious problem to water ecosystems. Hydrogen peroxide (H2O2) is an algaecide widely used in practice, but similar re-bloom problems are inevitably encountered. Our work found that Microcystis aeruginosa (M. aeruginosa) temporarily hibernates after H2O2 treatment, but there is still a risk of secondary outbreaks. Interestingly, the dormant period was as long as 20 and 28 days in 5 mg L-1 and 20 mg L-1 H2O2 treatment groups, respectively, but the photosynthetic activity was both restored much earlier (within 14 days). Subsequently, a quantitative imaging flow cytometry-based method was constructed and confirmed that the re-bloom had undergone two stages including first recovery and then re-division. The expression of ftsZ and fabZ genes showed that M. aeruginosa had active transcription processes related to cell division protein and fatty acid synthesis during the dormancy stat. Furthermore, metabolomics suggested that the recovery of M. aeruginosa was mainly by activating folate and salicylic acid synthesis pathways, which promoted environmental stress resistance, DNA synthesis, and cell membrane repair. This study reported the comprehensive mechanisms of secondary outbreak of M. aeruginosa after H2O2 treatment. The findings suggest that optimizing the dosage and frequency of H2O2, as well as exploring the potential use of salicylic acid and folic acid inhibitors, could be promising directions for future algal control strategies.

Toxic effects and action mechanism of metal-organic framework UiO-66-NH2 in Microcystisaeruginosa

The zirconium metal-organic framework UiO-66-NH2 has garnered considerable attention for their potentials of removing environmental contaminants from water. The production and application of UiO-66-NH2 make their releases into the aquatic environment inevitable. Nevertheless, little information is available regarding its potential risk to the environment and aquatic organisms, thus limiting the evaluation of its safe and sustainable use. In this study, the ecotoxicity of UiO-66-NH2 was evaluated, specifically its impacts on growth, extracellular organic matter release, and metabolomic changes of the model phytoplankton Microcystis aeruginosa (M. aeruginosa). UiO-66-NH2 exhibited moderate effects on algal physiology including growth, viability, and photosynthetic system. At concentrations below 20 mg/L, UiO-66-NH2 induced negligible inhibition of algal growth, algal viability, and photosynthesis. In contrast, UiO-66-NH2 boosted the release of extracellular organic matter even at concentration as low as 0.02 mg/L. These findings indicated that, while no evident damage to algal cells was observed, UiO-66-NH2 was hazardous to the aquatic environment as it stimulated the release of algal toxins. Moreover, UiO-66-NH2 entered algal cells rather than adhering to the surface of M. aeruginosa as observed by the fluorescence imaging. Based on metabolic analysis, UiO-66-NH2 influenced the cyanobacteria mainly through interference with purine metabolism and ABC transporter. This study sheds light on the potential threat UiO-66-NH2 posing to microalgae, and has potential implications for its safe utilization in the environmental field.

UV-A radiation increases biomass yield by enhancing energy flow and carbon assimilation in the edible cyanobacterium Nostoc sphaeroides

Ultraviolet (UV) A radiation (315-400 nm) is the predominant component of solar UV radiation that reaches the Earth's surface. However, the underlying mechanisms of the positive effects of UV-A on photosynthetic organisms have not yet been elucidated. In this study, we investigated the effects of UV-A radiation on the growth, photosynthetic ability, and metabolome of the edible cyanobacterium Nostoc sphaeroides. Exposures to 5-15 W m-2 (15-46 µmol photons m-2 s-1) UV-A and 4.35 W m-2 (20 μmol photons m-2 s-1) visible light for 16 days significantly increased the growth rate and biomass production of N. sphaeroides cells by 18%-30% and 15%-56%, respectively, compared to the non-UV-A-acclimated cells. Additionally, the UV-A-acclimated cells exhibited a 1.8-fold increase in the cellular nicotinamide adenine dinucleotide phosphate (NADP) pool with an increase in photosynthetic capacity (58%), photosynthetic efficiency (24%), QA re-oxidation, photosystem I abundance, and cyclic electron flow (87%), which further led to an increase in light-induced NADPH generation (31%) and ATP content (83%). Moreover, the UV-A-acclimated cells showed a 2.3-fold increase in ribulose-1,5-bisphosphate carboxylase/oxygenase activity, indicating an increase in their carbon-fixing capacity. Gas chromatography-mass spectrometry-based metabolomics further revealed that UV-A radiation upregulated the energy-storing carbon metabolism, as evidenced by the enhanced accumulation of sugars, fatty acids, and citrate in the UV-A-acclimated cells. Therefore, our results demonstrate that UV-A radiation enhances energy flow and carbon assimilation in the cyanobacterium N. sphaeroides.IMPORTANCEUltraviolet (UV) radiation exerts harmful effects on photo-autotrophs; however, several studies demonstrated the positive effects of UV radiation, especially UV-A radiation (315-400 nm), on primary productivity. Therefore, understanding the underlying mechanisms associated with the promotive effects of UV-A radiation on primary productivity can facilitate the application of UV-A for CO2 sequestration and lead to the advancement of photobiological sciences. In this study, we used the cyanobacterium Nostoc sphaeroides, which has an over 1,700-year history of human use as food and medicine, to explore its photosynthetic acclimation response to UV-A radiation. As per our knowledge, this is the first study to demonstrate that UV-A radiation increases the biomass yield of N. sphaeroides by enhancing energy flow and carbon assimilation. Our findings provide novel insights into UV-A-mediated photosynthetic acclimation and provide a scientific basis for the application of UV-A radiation for optimizing light absorption capacity and enhancing CO2 sequestration in the frame of a future CO2 neutral, circular, and sustainable bioeconomy.

Physiological regulation of microalgae under cadmium stress and response mechanisms of time-series analysis using metabolomics

The investigation of heavy metal wastewater treatment utilizing microalgae adsorption has been extensively demonstrated. However, the response mechanism based on metabolomics to analyze the time-series changes of microalgae under Cd stress has not been described in detail. In this study, SEM/TEM demonstrated that Cd accumulated on the cell surface of microalgae and was bioconcentrated in the cytoplasm, vesicles, and chloroplasts. Carbonyl/quinone/ketone/carboxyl groups (OCO), membrane polysaccharides (OH), and phospholipids (PO) were involved in the interaction of Cd ions, and the chlorophyll content underwent a process of decreasing in the early stage (1.62 mg/g at 48 h) and recovering to the normal level in the late stage, and the contents of MDA, GSH, and SOD were all increased (29.7 nmol/g, 0.23 mg/g, and 30.01 u/106 cells) and then gradually returned to the steady state. The results of EPS content and fluorescent labeling showed that Cd induced the overexpression and synthesis of extracellular polysaccharides and proteins, which is one of the defense mechanisms participating in the reduction of cellular damage by complexed Cd. Metabolomics results indicated that the malate synthesis pathway was activated after Cd-20 h, and the microalgal cells began to shift the metabolic pathway to storage lipid or polysaccharide biosynthesis. In the Calvin cycle, the expression of D-Sedoheptulose 7-phosphate in Cd-20 h_vs_ck and Cd-72 h_vs_Cd-20 h firstly declined and then increased, and the photosynthesis system was suppressed at the beginning, and then gradually returned to normal to maintain the successful development of the dark reaction. The results of time series analysis revealed that the response of microalgae to Cd was categorized into fast response and slow response to regulate cell adsorption and growth metabolism.

Resistance mechanisms of Saccharomyces cerevisiae against silver nanoparticles with different sizes and coatings

To investigate the underlying resistance mechanisms of Saccharomyces cerevisiae against Ag-NPs with different particle sizes and coatings, transcriptome sequencing (RNA-seq) technology was used to characterize the transcriptomes from S. cerevisiae exposed to 20-PVP-Ag, 100-PVP-Ag, 20-CIT-Ag and 100-CIT-Ag, respectively. The steroid biosynthesis was found as a general pathway for Ag-NPs stress responding, in which ERG6 and ERG3 were inhibited and ERG11, ERG25 and ERG5 were significantly up-regulated to resist the stress by supporting the later mutation and resistance and modulate drug efflux indirectly. The resistance mechanism of S. cerevisiae to 20-PVP-Ag seems different from that of 100-PVP-Ag, 20-CIT-Ag and 100-CIT-Ag. Under the 20-PVP-Ag, transmembrane transporter activity, transition metal ion homeostasis and oxidative phosphorylation pathway were main resistance pathways to enhance cell transport processes. While 100-PVP-Ag, 20-CIT-Ag and 100-CIT-Ag mainly impacted RNA binding, structural constituent of ribosome and ribosome pathway which can provide more energy to maintain the number and function of protein in cells. This study reveals the differences in resistance mechanisms of S. cerevisiae to Ag-NPs with different particle sizes and coatings, and explains several main regulatory mechanisms used to respond to silver stress. It will provide theoretical basis for the study of chemical risk assessment.

Repeated Exposure Enhanced Toxicity of Clarithromycin on Microcystis aeruginosa Versus Single Exposure through Photosynthesis, Oxidative Stress, and Energy Metabolism Shift

Antibiotics are being increasingly detected in aquatic environments, and their potential ecological risk is of great concern. However, most antibiotic toxicity studies involve single-exposure experiments. Herein, we studied the effects and mechanisms of repeated versus single clarithromycin (CLA) exposure on Microcystis aeruginosa. The 96 h effective concentration of CLA was 13.37 μg/L upon single exposure but it reduced to 6.90 μg/L upon repeated exposure. Single-exposure CLA inhibited algal photosynthesis by disrupting energy absorption, dissipation and trapping, reaction center activation, and electron transport, thereby inducing oxidative stress and ultrastructural damage. In addition, CLA upregulated glycolysis, pyruvate metabolism, and the tricarboxylic acid cycle. Repeated exposure caused stronger inhibition of algal growth via altering photosynthetic pigments, reaction center subunits biosynthesis, and electron transport, thereby inducing more substantial oxidative damage. Furthermore, repeated exposure reduced carbohydrate utilization by blocking the pentose phosphate pathway, consequently altering the characteristics of extracellular polymeric substances and eventually impairing the defense mechanisms of M. aeruginosa. Risk quotients calculated from repeated exposure were higher than 1, indicating significant ecological risks. This study elucidated the strong influence of repeated antibiotic exposure on algae, providing new insight into antibiotic risk assessment.

A New Type of Quantum Fertilizer (Silicon Quantum Dots) Promotes the Growth and Enhances the Antioxidant Defense System in Rice Seedlings by Reprogramming the Nitrogen and Carbon Metabolism

To promote the growth and yield of crops, it is necessary to develop an effective silicon fertilizer. Herein, a new type of 2 nm silicon quantum dot (SiQD) was developed, and the phenotypic, biochemical, and metabolic responses of rice seedlings treated with SiQDs were investigated. The results indicated that the foliar application of SiQDs could significantly improve the growth of rice seedlings by increasing the uptake of nutrient elements and activating the antioxidative defense system. Furthermore, metabolomics revealed that the supply of SiQDs could significantly up-regulate several antioxidative metabolites (oxalic acid, maleic acid, glycine, lysine, and proline) by reprogramming the nitrogen- and carbon-related biological pathways. The findings provide a new strategy for developing an effective and promising quantum fertilizer in agriculture.

Seed Priming with Reactive Oxygen Species-Generating Nanoparticles Enhanced Maize Tolerance to Multiple Abiotic Stresses

Climate change-induced extreme weather events (heat, cold, drought, and flooding) will severely affect crop production. Increasing the resilience of crops to fluctuating environmental conditions is critically important. Here, we report that nanomaterials (NMs) with reactive oxygen species (ROS)-generating properties can be used as seed priming agents to simultaneously enhance the tolerance of maize seeds and seedlings to diverse and even multiple stresses. Maize seeds primed with 40 mg/L silver nanoparticles (AgNPs) exhibited accelerated seed germination and an increased germination rate, greater seedling vigor, and better seedling growth under drought (10% and 20% PEG), saline (50 and 100 mM NaCl), and cold (15 °C) stress conditions, indicating enhanced resilience to diverse stresses. Importantly, maize resistance to simultaneous multiple stresses (drought and cold, drought and salt, and salt and cold) was markedly enhanced. Under drought conditions, seed priming significantly boosted root hair density and length (17.3-82.7%), which enabled greater tolerance to water deficiency. RNA-seq analysis reveals that AgNPs seed priming induced a transcriptomic shift in maize seeds. Plant hormone signal transduction and MAPK signaling pathways were activated upon seed priming. Importantly, low-cost and environmentally friendly ROS-generating Fe-based NMs (Fe2O3 and Fe3O4 NPs) were also demonstrated to enhance the resistance of seeds and seedlings to drought, salt, and cold stresses. These findings demonstrate that a simple seed priming strategy can be used to significantly enhance the climate resilience of crops through modulated ROS homeostasis and that this approach could be a powerful nanoenabled tool for addressing worsening food insecurity.

Effects of the application of nanoscale zero-valent iron on plants: Meta analysis, mechanism, and prospects

In order to determine the ideal conditions for the application of nanoscale zero-valent iron (nZVI) in agricultural production, this review studies the effects of nZVI application on plant physiological parameters, presents its mechanism and prospective outcomes. In this research, it was observed that the application of nZVI had both favorable and unfavorable effects on plant growth, photosynthesis, oxidative stress, and nutrient absorption levels. Specifically, the application of nZVI significantly increased the biomass and length of plants, and greatly reduced the germination rate of seeds. In terms of photosynthesis, there was no significant effect for the application of nZVI on the synthesis of photosynthetic pigments (chlorophyll and carotenoids). In terms of oxidative stress, plants respond by increasing the activity of antioxidant enzyme under mild nZVI stress and trigger oxidative burst under severe stress. In addition, the application of nZVI significantly increased the absorption of nutrients (B, K, P, S, Mg, Zn, and Fe). In summary, the application of nZVI can affect the plant physiological parameters, and the degree of influence varies depending on the concentration, preparation method, application method, particle size, and action time of nZVI. These findings are important for evaluating nZVI-related risks and enhancing nZVI safety in agricultural production.

Nanofibrous Dressing with Nanocomposite Monoporous Microspheres for Chemodynamic Antibacterial Therapy and Wound Healing

The excessive use of antibiotics and consequent bacterial resistance have emerged as crucial public safety challenges for humanity. As a promising antibacterial treatment, using reactive oxygen species (ROS) can effectively address this problem and has the advantages of being highly efficient and having low toxicity. Herein, electrospinning and electrospraying were employed to fabricate magnesium oxide (MgO)-based nanoparticle composited polycaprolactone (PCL) nanofibrous dressings for the chemodynamic treatment of bacteria-infected wounds. By utilizing electrospraying, erythrocyte-like monoporous PCL microspheres incorporating silver (Ag)- and copper (Cu)-doped MgO nanoparticles were generated, and the unique microsphere-filament structure enabled efficient anchoring on nanofibers. The composite dressings produced high levels of ROS, as confirmed by the 2,7-dichloriflurescin fluorescent probe. The sustained generation of ROS resulted in efficient glutathione oxidation and a remarkable bacterial killing rate of approximately 99% against Staphylococcus aureus (S. aureus). These dressings were found to be effective at treating externally infected wounds. The unique properties of these composite nanofibrous dressings suggest great potential for their use in the medical treatment of bacteria-infected injuries.

Extracellular polymeric substances altered the physicochemical properties of molybdenum disulfide nanomaterials to mitigate its toxicity to Chlorella vulgaris

Although the toxic effects of two-dimensional nanomaterials (2D-NMs) have been widely reported, the influence of extracellular polymeric substances (EPS) on the environmental fate and risk of 2D-NMs in aquatic environments is largely unknown, and the processes and mechanisms involved remain to be revealed. Herein, we investigated the impact of EPS secreted by microalgae (Chlorella vulgaris (C. vulgaris)) on the environmental transformation and risk of molybdenum disulfide (MoS2). We found that the attachment of EPS increased the thickness of MoS2 (from 2 nm to 5 nm), changed it from a monolayer sheet to a fuzzy multilayer structure, and promoted the formation of defects on MoS2. The blue-shift of the peak associated with the plasmon resonances in the 1 T phase and the generation of electron-hole pairs suggested that EPS altered the surface electronic structure of MoS2. EPS interacted mainly with the S atoms on the 1 T phase, and the attachment of EPS promoted the oxidation of MoS2. The reduction in hydrodynamic diameter (Dh) and the decrease in zeta potential indicated that EPS inhibited the agglomeration behavior of MoS2 and enhanced its dispersion and stability in aqueous media. Notably, EPS reduced the generation of free radicals (superoxide anion (•O2-), singlet oxygen (1O2), and hydroxyl radicals (•OH-)). Furthermore, EPS mitigated the toxicity of MoS2 to C. vulgaris, such as attenuated reduction in biomass and chlorophyll content. Compared to pristine MoS2, MoS2 + BG11 + EPS exhibited weaker oxidative stress, membrane damage and lipid peroxidation. The adsorption of EPS on MoS2 surface reduced the attachment sites of MoS2, making MoS2 less likely to be enriched on the cell surface. The findings have significant contribution for understanding the interactions between EPS and MoS2 in aquatic ecosystems, providing scientific guidance for risk assessment of 2D-NMs.

Blockage of ATPase-mediated energy supply inducing metabolic disturbances in algal cells under silver nanoparticles stress

Adenosine triphosphate (ATP) generation of aquatic organisms is often subject to nanoparticles (NPs) stress, involving extensive reprogramming of gene expression and changes in enzyme activity accompanied by metabolic disturbances. However, little is known about the mechanism of energy supply by ATP to regulate the metabolism of aquatic organisms under NPs stress. Here, we selected extensively existing silver nanoparticles (AgNPs) to investigate their implications on ATP generation and relevant metabolic pathways in alga (Chlorella vulgaris). Results showed that ATP content significantly decreased by 94.2% of the control (without AgNPs) in the algal cells at 0.20 mg/L AgNPs, which was mainly attributed to the reduction of chloroplast ATPase activity (81.4%) and the downregulation of ATPase-coding genes atpB and atpH (74.5%-82.8%) in chloroplast. Molecular dynamics simulations demonstrated that AgNPs competed with the binding sites of substrates adenosine diphosphate and inorganic phosphate by forming a stable complex with ATPase subunit beta, potentially resulting in the reduced binding efficiency of substrates. Furthermore, metabolomics analysis proved that the ATP content positively correlated with the content of most differential metabolites such as D-talose, myo-inositol, and L-allothreonine. AgNPs remarkably inhibited ATP-involving metabolic pathways, including inositol phosphate metabolism, phosphatidylinositol signaling system, glycerophospholipid metabolism, aminoacyl-tRNA biosynthesis, and glutathione metabolism. These results could provide a deep understanding of energy supply in regulating metabolic disturbances under NPs stress.

Metabolomic profiles reveals the dose-dependent effects of rice grain yield and nutritional quality upon exposure zero-valent iron nanoparticles

Zero-valent iron nanoparticles (nZVI) were widely used material in environmental remediation, which has attracted increasing concern for their safety. Previous studies have shown that the addition of nZVI could inhibit rice seedling growth. However, the effect of nZVI on the soil-rice system during the entire life cycle was not reported. Furthermore, the effect of nZVI on the quality of rice grain has also not been studied. Therefore, we investigated the effects of rice grain yield and nutritional quality upon exposure nZVI. The results showed that the soil pH value, redox potential and Fe (II) content in the nZVI-treated group were decreased in a dose-dependent manner. Interestingly, 2500 mg/kg nZVI significantly decreased the relative abundance of several functional microbial communities (10.52-73.53 %) associated with carbon and nitrogen cycles in response to plants compared to the control. Meanwhile, the nZVI treatment clearly reduced grain yield (8.71-18.21 %). Furthermore, the content of protein (51.72-57.79 %) and several essential nutrients (Zn, Cu, Mn and Mo) in the nZVI-treated grains was also decreased in a dose-dependent manner. The results of grain metabolomics indicated that nZVI could interfere with the relative expression of lysine and glutathione by regulating the metabolic pathways of antioxidant and protein synthesis in rice.

Unraveling the intracellular and extracellular self-defense of Chlorella sorokiniana toward highly toxic pyridine stress

A bottleneck of microalgae-based techniques for wastewater bioremediation is activity inhibition of microalgae by toxic pollutants. The defense strategies of Chlorella sorokinana against toxic pyridine were studied. Results indicated that pyridine caused photoinhibition and reactive oxygen species overproduction in a concentration-dependent manner. The 50% inhibitory concentration of pyridine (147 mg L^-1) destroyed C/N balance, disrupted multiple metabolic pathways of C. sorokinana. In response to pyridine stress, ascorbate peroxidase and catalase activities increased to scavenge reactive oxygen species under pyridine concentrations lower than 23 mg L^-1. At higher pyridine concentrations, the activation of calcium signaling pathways and phytohormones represented the predominant defense response. Extracellular polymeric substances increased 3.6-fold in 147 mg L^-1 group than control, which interacted with pyridine through hydrophobic and aromatic stacking to resist pyridine entering algal cells. Unraveling the intracellular and extracellular self-defense mechanisms of microalgae against pyridine stress facilitates the development of microalgal-based technology in wastewater bioremediation.

Potential effects of Ag ion on the host by changing the structure of its gut microbiota

Silver (Ag) can change the structure of the gut microbiota (GM), but how such change may affect host health is unknown. In this study, mice were exposed to silver acetate daily for 120 days. During this period, Ag accumulation in the liver was measured, its effects on GM structure were analyzed, and potential metabolic changes in liver and serum were examined. Although Ag accumulation remained unchanged in most treatments, the ratio of Firmicutes to Bacteroidetes at the phylum level increased and changes in the relative abundance of 33 genera were detected, suggesting that Ag altered the energy metabolism of mice via changes in the gut GM. In serum and liver, 34 and 72 differentially expressed metabolites were identified, respectively. The KEGG pathways thus enriched mainly included those involving the metabolism of amino acids, organic acids, lipids, and purine. Strong correlations were found between 33 % of the microorganisms with altered relative abundances and 46 % of the differentially expressed metabolites. The resulting clusters yielded two communities responsible for host inflammation and energy metabolism. Overall, these results demonstrate potential effects of Ag on the host, by changing its GM structure, and the need to consider them when evaluating the health risk of Ag.

Engineering Climate-Resilient Rice Using a Nanobiostimulant-Based "Stress Training" Strategy

Under a changing climate, cultivating climate-resilient crops will be critical to maintaining food security. Here, we propose the application of reactive oxygen species (ROS)-generating nanoparticles as nanobiostimulants to trigger stress/immune responses and subsequently increase the stress resilience of plants. We established three regimens of silver nanoparticles (AgNPs)-based "stress training": seed training (ST), leaf training (LT), and combined seed and leaf training (SLT). Trained rice seedlings were then exposed to either rice blast fungus (Magnaporthe oryzae) or chilling stress (10 °C). The results show that all "stress training" regimes, particularly SLT, significantly enhanced the resistance of rice against the fungal pathogen (lesion size reduced by 82% relative to untrained control). SLT also significantly enhanced rice tolerance to cold stress. The mechanisms for the enhanced resilience were investigated with metabolomics and transcriptomics, which show that "stress training" induced considerable metabolic and transcriptional reprogramming in rice leaves. AgNPs boosted ROS-activated stress signaling pathways by oxidative post-translational modifications of stress-related kinases, hormones, and transcriptional factors (TFs). These signaling pathways subsequently modulated the expression of defense genes, including specialized metabolites (SMs) biosynthesis genes, cell membrane lipid metabolism genes, and pathogen-plant interaction genes. Importantly, results showed that the "stress memory" can be transferred transgenerationally, conferring offspring seeds with improved seed germination and seedling vigor. This may provide an epigenetic breeding strategy to fortify stress resilience of crops. This nanobiostimulant-based stress training strategy will increase yield vigor against a changing climate and will contribute to sustainable agriculture by reducing agrochemical use.

Metabolomics reveals size-dependent persistence and reversibility of silver nanoparticles toxicity in freshwater algae

Although the toxicity of silver nanoparticles (AgNPs) has been widely reported, the persistence and reversibility of AgNPs toxicity are poorly understood. In the present work, AgNPs with particle sizes of 5 nm, 20 nm, and 70 nm (AgNPs5, AgNPs20, and AgNPs70) were selected to investigate the nanotoxicity and recovery effects of Chlorella vulgaris in the exposure (72 h) and recovery (72 h) stages using non-targeted metabolomics techniques. The exposure of AgNPs exerted size-dependent effects on several aspects of C. vulgaris physiology, including growth inhibition, chlorophyll content, intracellular silver accumulation, and differential expression of metabolites, and most of these adverse effects were reversible. Metabolomics revealed that AgNPs with small sizes (AgNPs5 and AgNPs20) mainly inhibited glycerophospholipid and purine metabolism, and the effects were reversible. In contrast, AgNPs with large sizes (AgNPs70) reduced amino acid metabolism and protein synthesis by inhibiting aminoacyl-tRNA biosynthesis, and the effects were irreversible, demonstrating the persistence of nanotoxicity of AgNPs. The size-dependent persistence and reversibility of AgNPs toxicity provides new insights to further understand the mechanisms of toxicity of nanomaterials.

Antagonism toxicity of CuO nanoparticles and mild ocean acidification to marine algae

The toxicity of CuO nanoparticles (NPs) to marine microalgae (Emiliania huxleyi) under ocean acidification (OA) conditions (pHs 8.10, 7.90, 7.50) was investigated. CuO NPs (5.0 mg/L) caused significant toxicity (e.g., 48-h growth inhibition, 20%) under normal pH (8.10), and severe OA (pH 7.50) increased the toxicity of CuO NPs (e.g., 48-h growth inhibition, 68%). However, toxicity antagonism was observed with a growth inhibition (48 h) decreased to 37% after co-exposure to CuO NPs and mild OA (pH 7.90), which was attributed to the released Cu²⁺ ions from CuO NPs. Based on biological responses as obtained from RNA-sequencing, the dissolved Cu²⁺ ions (0.078 mg/L) under mild OA were found to increase algae division (by 17%) and photosynthesis (by 28%) through accelerating photosynthetic electron transport and promoting ATP synthesis. In addition, mild OA enhanced EPS secretion by 41% and further increased bioavailable Cu²⁺ ions, thus mitigating OA-induced toxicity. In addition, excess Cu²⁺ ions could be transformed into less toxic Cu₂S and Cu₂O based on X-ray absorption near-edge spectroscopy (XANES) and high-resolution transmission electron microscopy (HR-TEM), which could additionally regulate the antagonism effect of CuO NPs and mild OA. The information advances our knowledge in nanotoxicity to marine organisms under global climate change.

Insights into growth-affecting effect of nanomaterials: Using metabolomics and transcriptomics to reveal the molecular mechanisms of cucumber leaves upon exposure to polystyrene nanoplastics (PSNPs)

Polystyrene nanoplastics (PSNPs, <100nm), an artificial pollutant that is widespread in the environment, can be assimilated by plants to alter plant gene expression and its metabolic pathway; thus, interfering with physiological homeostasis and growth of plants. Recently, the biosafety and potential environmental risks of PSNPs have attracted enormous attention. However, the knowledge regarding the uptake and phytotoxicity of atmosphere PSNPs subsiding to plant leaves is still limited. Here, we separately applied 50 mg/L and 100 mg/L PSNPs on cucumber leaves to simulate the plant response to the atmosphere PSNPs. We found that the PSNPs can be accumulated on the surface of cucumber leaves and are also able to be uptake by cucumber leaf stomata. The repertoires of metabolomics and transcriptomics from cucumber leaves upon PSNPs treatment demonstrated that the deposition of PSNPs on leaves alters the biosynthesis of various metabolites and the expression of a variety of genes. The leaves exposure to low concentration (50 mg/L) of PSNPs impact the genes involved in carbohydrate metabolism and the biosynthesis of metabolites related to membrane stability maintenance, thereby, probably enhancing plant tolerance to the stress caused by PSNPs. Whereas, exposure to high concentration (100 mg/L) of PSNPs, both nitrogen and carbohydrate metabolism in cucumber leaves are affected, as well as that the photosynthetic capacity was decreased, leading to the threat to plant health. Combined omics technologies, our findings advance our understanding about how the PSNPs released to ecological environment influence the terrestrial plant growth and provide phytotoxic mechanism.

Nanoparticles and antibiotics stress proliferated antibiotic resistance genes in microalgae-bacteria symbiotic systems

The comprehensive effect of exogenous pollutants on the dispersal and abundance of antibiotic-resistance genes (ARGs) in the phycosphere, bacterial community and algae-bacteria interaction remains poorly understood. We investigated community structure and abundance of ARGs in free-living (FL) and particle-attached (PA) bacteria in the phycosphere under nanoparticles (silver nanoparticles (AgNPs) and hematite nanoparticles (HemNPs)) and antibiotics (tetracycline and sulfadiazine) stress using high-throughput sequencing and real-time quantitative PCR. Meanwhile, the intrinsic connection of algae-bacteria interaction was explored by transcriptome and metabolome. The results showed that the relative abundance of sulfonamide and tetracycline ARGs in PA and FL bacteria increased 103-129 % and 112-134 %, respectively, under combined stress of nanoparticles and antibiotics. Antibiotics have a greater effect on ARGs than nanoparticles at environmentally relevant concentrations. Proteobacteria, Firmicutes, and Bacteroidetes, as the primary potential hosts of ARGs, were the dominant phyla. Lifestyle, i.e., PA and FL, significantly determined the abundance of ARGs and bacterial communities. Moreover, algae can provide bacteria with nutrients (carbohydrates and amino acids), and can also produce antibacterial substances (fatty acids). This algal-bacterial interaction may indirectly affect the distribution and abundance of ARGs. These findings provide new insights into the distribution and dispersal of ARGs in microalgae-bacteria symbiotic systems.

AgNPs-Triggered Seed Metabolic and Transcriptional Reprogramming Enhanced Rice Salt Tolerance and Blast Resistance

Seeds are facing harsher environments due to the changing climate. Improving seeds' stress resilience is critical to reduce yield loss. Here, we propose that using ROS-generating nanoparticles (NPs) to prestimulate seeds would enhance the stress resilience of seeds and seedlings through triggering stress/immune responses. We examined this hypothesis by exposing AgNPs-primed rice (Oryza sativa L.) seeds under salt conditions (NaCl). The results showed that primed seeds exhibit accelerated germination speed, increased seedling vigor (from 22.5 to 47.6), biomass (11%), and root length (83%) compared to seeds with hydropriming treatment. Multiomics (metabolomics and transcriptomics) analyses reveal that AgNPs-priming triggered metabolic and transcriptional reprogramming in rice seeds. Signaling metabolites, such as salicylic acid, niacinamide, and glycerol-3-phosphate, dramatically increased upon AgNPs-priming. KEGG pathway analysis reveals that AgNPs-priming activated stress signaling and defense related pathways, such as plant hormone signal transduction, glutathione metabolism, flavone and flavonol biosynthesis, MAPK signaling pathway, and plant-pathogen interaction. These metabolic and transcriptional changes indicate that AgNPs-priming triggered stress/immune responses. More importantly, this "stress memory" can last weeks, providing protection to rice seedlings against salt stress and rice blast fungus (Magnaporthe oryzae). Overall, we show that prestimulated seeds with ROS-generating AgNPs not only enable faster and better germination under stress conditions, but also increase seedling resistance to biotic and abiotic stresses. This simple nanobiostimulant-based strategy may contribute to sustainable agriculture by maintaining agricultural production and reducing the use of pesticides.

Effects of WS2 Nanosheets on N2-fixing Cyanobacteria: ROS overproduction, cell membrane damage, and cell metabolic reprogramming

The ecotoxicity of tungsten disulfide (WS₂) nanomaterials remains unclear so far. Here, the toxicity of WS₂ nanosheets on N₂-fixing cyanobacteria (Nostoc sphaeroides) was evaluated. Specifically, Nostoc were cultivated in media spiked with different concentrations of WS₂ nanosheets (0, 0.05, 0.1 and 0.5 mg/L) for 96 h. Relative to unexposed cells, WS₂ nanosheets at 0.5 mg/L significantly decreased cell density, content of total sugar and protein by 10.9 %, 0.43 %, and 6.1 %, respectively. Gas chromatography-mass spectrometry (GC-MS)-based metabolomics revealed that WS₂ nanosheets exposure altered the metabolite profile of Nostoc in a dose-dependent manner. Energy metabolism related pathways, including the Calvin-Benson-Bassham (CBB) cycle and tricarboxylic acid (TCA) cycle, were significantly inhibited. In addition, WS₂ nanosheets exposure resulted in downregulation (20-40 %) of S-containing amino acids (cystine, methionine, and cysteine) and sulfuric acid. Additionally, fatty acids and antioxidant-related compounds (formononetin, catechin, epigallocatechin, dehydroascorbic acid, and alpha-tocopherol) in Nostoc were drastically decreased by 4-50 % upon exposure to WS₂ nanosheets, which implies oxidative stress induced by the nanomaterials. Biochemical assays for reactive oxygen species (ROS) and malondialdehyde (MDA) confirmed that WS₂ nanosheets triggered ROS overproduction and induced lipid peroxidation. Taken together, WS₂ exposure perturbed carbon (C), nitrogen (N), and sulfate (S) metabolism of Nostoc, which may influence C, N, and S cycling, given the important roles of cyanobacteria in these processes. These results highlight the need for caution in the application and environmental release of WS₂ nanomaterials to prevent unintended environmental impacts due to their potential ecotoxicity.

Untargeted Metabolomic Approach of Curcuma longa to Neurodegenerative Phytocarrier System Based on Silver Nanoparticles

Curcuma is one of the most famous medicinal and tropical aromatic plants. Its health benefits have been appreciated and exploited in traditional Asian medicine since ancient times. Various studies have investigated its complex chemical composition and demonstrated the remarkable therapeutic properties of curcuma's phytoconstituents. Oxidative stress is a decisive driving factor triggering numerous pathologies (neurodegenerative, psychiatric and cardiovascular diseases; diabetes; tumors, etc.). Numerous recent studies have focused on the use of natural compounds and nanomaterials as innovative molecular targeting agents as effective therapeutic strategies. In this study, we report, for the first time, the development of a simple target phytocarrier system that capitalizes on the bioactive properties of curcuma and AgNPs. The complete metabolic profile of curcuma was determined based on gas chromatography-mass spectrometry (GC-MS) and electrospray ionization quadrupole time-of-flight mass spectrometry (ESI-QTOF-MS). A total of 80 metabolites were identified under mass spectra (MS)-positive mode from 10 secondary metabolite categories: terpenoids, amino acids, diarylheptanoids, flavonoids, phenolic acids, steroids, fatty acids, coumarins, alkaloids and miscellaneous. In addition, the biological activity of each class of metabolites was discussed. A comprehensive characterization (FT-IR, UV-Vis, DLS, SEM, TEM, EDS, zeta potential and XRD) was performed to study the morphostructural properties of this new phytocarrier system. Antioxidant activity of the new phytocarrier system was evaluated using a combination of in vitro methods (total phenolic assay, 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay and cyclic voltammetric method (Trolox equivalent antioxidant capacity (TEAC) electrochemical assay)). Antioxidants assays showed that the phytocarrier system exhibits superior antioxidant properties to those of its components, i.e., curcuma or citrate-coated-AgNPs. These data confirm the potential to enhance relevant theoretical knowledge in the area of innovative antioxidant agents, with potential application in neurodegenerative therapeutic strategies.

Biological responses of alga Euglena gracilis to triclosan and galaxolide and the regulation of humic acid

Although the toxicity of triclosan (TCS) and galaxolide (HHCB) in freshwater has been reported, little study is shed light on their molecular toxicity mechanism and the regulation of humic acid (HA). In this work, freshwater algae E. gracilis was selected to explore these processes, and the molecular toxicity mechanism was analyzed by metabolomics. TCS was more toxic to E. gracilis than HHCB at 1 d exposure with the EC₅₀ value of 0.76 mg L^-1, but HHCB showed a higher toxicity as the exposure time prolonged. HA could alleviate the toxicity of TCS and HHCB, mainly due to the inhibition of TCS uptake and oxidative stress, respectively. The perturbations on a number of antioxidant defense-related metabolites in response to TCS or HHCB also indicated oxidative stress was a main toxicity mechanism. However, the exposure to HHCB resulted in more pronounced perturbations in the purine metabolism than TCS, implying that HHCB may pose a genetic toxicity on algae. It may explain the higher toxicity of HHCB to algae as the exposure time increased. These findings provide a comprehensive understanding on the ecological risks of TCS or HHCB in natural waters.

Photosynthetic, antioxidative, and metabolic adjustments of a crop plant to elevated levels of La and Ce exposure

Rare earth elements (REEs) have been widely applied as fertilizers in farmland of China for decades to improve the yield and quality of crops. Unfortunately, adverse effects on plants have been observed due to overdosing with REEs. Until now, the toxicology of REEs was mainly evaluated based on phenotypic responses, but knowledge gaps still exist concerning their metabolic effects. Here, the physiological responses and nontargeted metabolomics studies were combined to systematically explore the potential effects of La and Ce on a crop plant, wheat Triticum aestivum. It was observed that REEs accumulated in the shoots of wheat, with significant reduction of the shoot biomass at higher exposure doses. The disturbance of photosynthesis and induced oxidative stress were identified by analyzing indicators of the photosynthetic (chlorophyll a/b, carotenoid and rubisco) and antioxidant systems (POD, CAT, SOD, GSH and MDA). Furthermore, the global metabolic profiles of REEs treatment groups and the non-exposed control group were screened and compared, and the metabolomic disturbance of REEs was dose-dependent. A high overlap of significantly changed metabolites and matched disturbed biological pathways was found between La and Ce treatments, indicating similarity of their toxicity mechanism in wheat shoots. Generally, the perturbed metabolomic pathways were mainly related to carbohydrate, amino acid and nucleotide/side metabolism, suggesting a disturbance of carbon and nitrogen metabolism, which finally affected the growth of wheat. We thus proved the potential adverse effect of inappropriate application of REEs in crop plants and postulated metabolomics as a feasible tool to identify the underlying toxicological mechanisms.

Identification and toxicity towards aquatic primary producers of the smallest fractions released from hydrolytic degradation of polycaprolactone microplastics

Bioplastics are thought as a safe substitute of non-biodegradable polymers. However, once released in the environment, biodegradation may be very slow, and they also suffer abiotic fragmentation processes, which may give rise to different fractions of polymer sizes. We present novel data on abiotic hydrolytic degradation of polycaprolactone (PCL), tracking the presence of by-products during 132 days by combining different physicochemical techniques. During the study a considerable amount of two small size plastic fractions were found (up to ∼ 6 mg of PCL by-product/g of PCL beads after 132 days of degradation); and classified as submicron-plastics (sMPs) from 1 μm to 100 nm and nanoplastics (NPs, <100 nm) as well as oligomers. The potential toxicity of the smallest fractions, PCL by-products < 100 nm (PCL-NPs + PCL oligomers) and the PCL oligomers single fraction, was tested on two ecologically relevant aquatic primary producers: the heterocystous filamentous nitrogen-fixing cyanobacterium Anabaena sp. PCC 7120, and the unicellular cyanobacterium Synechococcus sp. PCC 7942. Upon exposure to both, single and combined fractions, Reactive Oxygen Species (ROS) overproduction, intracellular pH and metabolic activity alterations were observed in both organisms, whilst membrane potential and morphological damages were only observed upon PCL-NPs + PCL oligomers exposure. Notably both PCL by-products fractions inhibited nitrogen fixation in Anabaena, which may be clearly detrimental for the aquatic trophic chain. As conclusion, fragmentation of bioplastics may render a continuous production of secondary nanoplastics as well as oligomers that might be toxic to the surrounding biota; both PCL-NPs and PCL oligomers, but largely the nanoparticulate fraction, were harmful for the two aquatic primary producers. Efforts should be made to thoroughly understand the fragmentation of bioplastics and the toxicity of the smallest fractions resulting from that degradation.

Metabolic impacts of polystyrene microplastics on the freshwater microalga Microcystis aeruginosa

Microplastics (plastic particles < 5 mm; MPs) are ubiquitous in aquatic environments but their potential adverse ecological effects on biota remain poorly understood. This is in part because in typical ecotoxicology tests the toxic effects of MPs were found to be limited. To capture the potential find-scale effects of MPs on freshwater organisms, we employed ultra-performance liquid chromatography-tandem mass spectrometry based untargeted metabolomics to investigate the metabolic impact of polystyrene microbeads microplastics (PS-MPs) of different sizes (0.1, 1, 10, 100 μm) and concentrations (1, 10, 100 mg/L) on a common freshwater microalga, Microcystis aeruginosa, after a 96-h exposure test. The phenotype-based results illustrated that while PS-MPs had no discernible effects on microalgal growth and photosynthesis, both oxidative stress and microcystin production were slightly increased. Metabolomics analysis revealed that the PS-MPs altered the global metabolic profile of the microalga. Specially, PS-MPs of larger size and higher concentration induced a larger number of differentially expressed metabolites. The PS-MPs significantly disturbed metabolisms involved in amino acid synthesis, membrane formation, nitrogen storage, and antioxidant defense of the microalga, consistent with the phenotypic observations. These results suggested several perturbed metabolic pathways, especially arginine-related pathways, as the mechanism. Our study showed that the insights provided by metabolomics-based approaches can enhance assessments of the ecological impacts of MPs on freshwater organisms.

Metabolic alterations in alga Chlamydomonas reinhardtii exposed to nTiO2 materials

Nano-sized titanium dioxide (nTiO2) is one of the most commonly used materials, however the knowledge about the molecular basis for metabolic and physiological changes in phytoplankton is yet to be explored. In the present study we use a combination of targeted metabolomics, transcriptomics and physiological response studies to decipher the metabolic perturbation in green alga Chlamydomonas reinhardtii exposed for 72 h to increasing concentrations (2, 20, 100 and 200 mg L-1) of nTiO2 with primary sizes of 5, 15 and 20 nm. Results show that the exposure to all three nTiO2 materials induced perturbation of the metabolism of amino acids, nucleotides, fatty acids, tricarboxylic acids, antioxidants but not in the photosynthesis. The alterations of the most responsive metabolites were concentration and primary size-dependent despite the significant formation of micrometer-size aggregates and their sedimentation. The metabolic perturbations corroborate the observed physiological responses and transcriptomic results and confirmed the importance of oxidative stress as a major toxicity mechanism for nTiO2. Transcriptomics revealed also an important influence of nTiO2 treatments on the transport, adenosine triphosphate binding cassette transporters, and metal transporters, suggesting a perturbation in a global nutrition of the microalgal cell, which was most pronounced for exposure to 5 nm nTiO2. The present study provides for the first-time evidence for the main metabolic perturbations in green alga C. reinhardtii exposed to nTiO2 and helps to improve biological understanding of the molecular basis of these perturbations.

Integrative chemical and omics analyses reveal copper biosorption and tolerance mechanisms of Bacillus cereus strain T6

A comprehensive understanding of the cellular response of microbes to metal stress is necessary for the rational development of microbe-based biosorbents for metal removal. The present study investigated the copper (Cu) sorption and resistance mechanism of Bacillus cereus strain T6, a newly isolated Cu-resistant bacterium, by integrative analyses of physiochemistry, genomics, transcriptomics, and metabolomics. The growth inhibition assay and biosorption determination showed that this bacterium exhibited high tolerance to Cu, with a minimum inhibitory concentration of 4.0 mM, and accumulated Cu by both extracellular adsorption and intracellular binding. SEM microscopic images and FTIR spectra showed significant cellular surface changes at the high Cu level but not at low, and the involvement of surface functional groups in the biosorption of Cu, respectively. Transcriptomic and untargeted metabolomic analyses detected 362 differentially expressed genes and 60 significantly altered metabolites, respectively. Integrative omics analyses revealed that Cu exposure dramatically induced a broad spectrum of genes involved in Cu transport and iron homeostasis, and suppressed the denitrification pathway, leading to significant accumulation of metabolites for metal transporter synthesis, membrane remolding, and antioxidant activities. The results presented here provide a new perspective on the intricate regulatory network of Cu homeostasis in bacteria.

Efficient inhibition of cyanobacteria M. aeruginosa growth using commercial food-grade fumaric acid

The control of cyanobacteria blooms is a global challenge. Here, we reported the efficient inhibition of M. aeruginosa by fumaric acid (FA), an intermediate metabolite of the tricarboxylic acid cycle. FA showed strong algicidal activity with an inhibition rate of 90.5% on the 8th day at a dose of 40 mg/L. The presence of FA caused severe membrane damage, as suggested by the fluorescence flow cytometry and morphology analysis. FA inhibited the formation of chlorophyll a, interrupting the photosynthesis system. It also induced oxidative stress in cells. Principal component analysis of the indicators suggested that the FA-treated sample had a significantly different inhibitory pattern than the acid-treated sample. Thus, the inhibitory effect was not solely caused by the pH effect. Untargeted metabolomic analysis revealed that 31 metabolites were differentially expressed in response to FA stress, which were mainly involved in the metabolite processes and the membranes. A commercial food-grade FA was able to inhibit the growth of M. aeruginosa similar to the analytical-grade FA. Our results suggest that FA can be potentially an efficient and low-risk chemical for inhibiting M. aeruginosa growth, which may find future applications in cyanobacteria bloom control.

Acetylacetone Interferes with Carbon and Nitrogen Metabolism of Microcystis aeruginosa by Cutting Off the Electron Flow to Ferredoxin

The regulation of photosynthetic machinery with a nonoxidative approach is a powerful but challenging strategy for the selective inhibition of bloom-forming cyanobacteria. Acetylacetone (AA) was recently found to be a target-selective cyanocide for Microcystis aeruginosa, but the cause and effect in the studied system are still unclear. By recording of the chemical fingerprints of the cells at two treatment intervals (12 and 72 h with 0.1 mM AA) with omics assays, the molecular mechanism of AA in inactivating Microcystis aeruginosa was elucidated. The results clearly reveal the effect of AA on ferredoxin and the consequent effects on the physiological and biochemical processes of Microcystis aeruginosa. In addition to its role as an electron acceptor of photosystem I, ferredoxin plays pivotal roles in the assimilation of nitrogen in cyanobacterial cells. The effect of AA on ferredoxin and on nonheme iron of photosystem II first cut off the photosynthetic electron transfer flow and then interrupted the synthesis of adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide phosphate (NADPH), which ultimately might affect carbon fixation and nitrogen assimilation metabolisms. The results here provide missing pieces in the current knowledge on the selective inhibition of cyanobacteria, which should shed light on the better control of harmful blooms.

Changes in primary metabolites and volatile organic compounds in cotton seedling leaves exposed to silver ions and silver nanoparticles revealed by metabolomic analysis

In the area of climate change, nanotechnology provides handy tools for improving crop production and assuring sustainability in global agricultural system. Due to excellent physiological and biochemical properties, silver nanoparticles (AgNPs) have been widely studied for potential use in agriculture. However, there are concerns about the mechanism of the toxic effects of the accumulation of AgNPs on crop growth and development. In this study, the impacts of AgNPs on cotton (Gossypium hirsutum) seedlings were evaluated by integrating physiological and comprehensive metabolomic analyses. Potting-soil-grown, two-week-old cotton seedlings were foliar-exposed to 5 mg/plant AgNP or 0.02 mg/plant Ag⁺ (equivalent to the free Ag⁺ released from AgNPs). Primary metabolites and volatile organic compounds (VOCs) were identified by gas chromatography-mass spectrometry (GC-MS) and solid-phase microextraction (SPME) GC-MS, respectively. AgNPs inhibited the photosynthetic capacity of the cotton leaves. The metabolic spectrum analysis identified and quantified 73 primary metabolites and 45 VOCs in cotton leaves. Both treatments significantly changed the metabolite profiles of plant leaves. Among the primary metabolites, AgNPs induced marked changes in amino acids, sugars and sugar alcohols. Among the VOCs, 13 volatiles, mainly aldehydes, alkanes and terpenoids, were specifically altered only in response to AgNPs. In summary, our study showed that the comprehensive influence of AgNPs on primary metabolites and VOCs was not merely attributed to the released Ag⁺ but was caused by AgNP-specific effects on cotton leaves. These results provide important knowledge about the physiological and chemical changes in cotton leaves upon exposure to AgNPs and offer a new insight for supporting the sustainable use of AgNPs in agriculture.

Exploration of defense and tolerance mechanisms in dominant species of mining area - Trifolium pratense L. upon exposure to silver

This present study investigated detoxification mechanisms of leguminous forage Trifolium pratense L. (red clover) seedlings upon exposure to Ag ions (Ag⁺) on an atomic level. Depressed plant growth (maximum inhibition rate: 46.57%) and significantly altered antioxidase/antioxidant substances levels (maximum inhibition rate: 65.45%/55.41%) revealed that the physiological metabolism was disturbed. Notable lesions were observed in both leaf and root cells at 588 μM Ag⁺ treatment. All differentially expressed genes (DEGs) were remarkably mapped to biological metabolism related pathways. Red clover seedlings were speculated to initially transform and immobilize Ag⁺ in the culture medium, then transporting and fixing them inside the cell, mainly as unreduced Ag⁺ bound to oxygen-, nitrogen-, sulfur-, chloride-containing biological molecules. A portion of Ag⁺ was reduced to Ag⁰ and aggregated to form crystalline argentiferous nanoparticles. Effective reducing agents such as alcohols, carboxylic acid, and etc, which are capable of coordinating heavy metals to reduce and stabilize them, were assumed to play a role in Ag⁺ reduction. The research results are of great value to understand the defense and tolerance mechanisms of red clover to Ag⁺ and explore the main existing forms of Ag⁺ in vivo and in vitro, which could indicate contamination condition in regional ecological environment such as mining area and its potential effects.

AgNPs seed priming accelerated germination speed and altered nutritional profile of Chinese cabbage

In this study, the performance of AgNPs-priming (20, 40, and 80 mg/L) on the seed germination, yield, and nutritional quality of Chinese cabbage were evaluated. We found that AgNPs-priming at 20 and 40 mg/L for 15 h significantly accelerated seed germination speed and seedling development. Cabbage seeds primed with different concentrations of AgNPs (0, 20, 40, and 80 mg/L) were then planted in a real soil and allowed to grow for 1 month in greenhouse. Results showed that AgNPs-priming at 40 mg/L significantly increased cabbage yield by 44.3%. Gas chromatography-mass spectrometry (GC-MS) combining with sparse partial least squares-discriminant analysis (sPLS-DA) reveals that AgNPs priming altered the metabolite profile of cabbage leaves in a dose-dependent manner, decreasing carbohydrates and increasing nitrogen related compounds. This indicates that the metabolic stimulation during germination stage can influence the entire life cycle of cabbage. The nutritional quality of cabbage edible leaves was evaluated by liquid chromatography with tandem mass spectrometry (LC-MS/MS) and inductively coupled plasma-mass spectrometry (ICP-MS). Results showed that AgNPs-priming at all tested concentrations significantly increased the content of essential amino acids for several folds in cabbage leaves, including alanine, aspartic acid, glutamine, glutamic acid, histidine, isoleucine, leucine, lysine, phenylalanine, proline, serine, threonine, tyrosine, and valine. Meanwhile, AgNPs-priming (40 mg/L) significantly increased iron (Fe) content by 23.8% in cabbage leaves. Ag did not bioaccumulate in edible tissues, indicating the bio-safety of AgNPs-priming. These results suggest that AgNPs-priming is a low-cost and eco-friendly approach to increase crop yield and nutritional quality.

Genomic and proteomic insights into the heavy metal bioremediation by cyanobacteria

Heavy metals (HMs) pose a global ecological threat due to their toxic effects on aquatic and terrestrial life. Effective remediation of HMs from the environment can help to restore soil's fertility and ecological vigor, one of the key Sustainable Development Goals (SDG) set by the United Nations. The cyanobacteria have emerged as a potential option for bioremediation of HMs due to their unique adaptations and robust metabolic machineries. Generally, cyanobacteria deploy multifarious mechanisms such as biosorption, bioaccumulation, activation of metal transporters, biotransformation and induction of detoxifying enzymes to sequester and minimize the toxic effects of heavy metals. Therefore, understanding the physiological responses and regulation of adaptation mechanisms at molecular level is necessary to unravel the candidate genes and proteins which can be manipulated to improve the bioremediation efficiency of cyanobacteria. Chaperons, cellular metabolites (extracellular polymers, biosurfactants), transcriptional regulators, metal transporters, phytochelatins and metallothioneins are some of the potential targets for strain engineering. In the present review, we have discussed the potential of cyanobacteria for HM bioremediation and provided a deeper insight into their genomic and proteomic regulation of various tolerance mechanisms. These approaches might pave new possibilities of implementing genetic engineering strategies for improving bioremediation efficiency with a future perspective.

Aquatic macrophytes mitigate the short-term negative effects of silver nanoparticles on denitrification and greenhouse gas emissions in riparian soils

Silver nanoparticles (AgNPs) are increasingly released into the aquatic environments because of their extensive use in consumer products and industrial applications. Some researchers have explored the toxicity of AgNPs to nitrogen (N) and carbon (C) cycles, but little is known about the role of aquatic plants in regulating the impact of AgNPs on these biogeochemical processes and related microorganisms. Here, two 90-day pot experiments were conducted to determine the effect of AgNPs on denitrification rates and greenhouse gas emissions in riparian wetland soils, with or without emergent plants (Typha minima Funck). As a comparison, the toxicity of equal concentration of AgNO₃ was also determined. The results showed that AgNPs released a great quantity of free Ag⁺, most of which was accumulated in soils, while little (less than 2%) was absorbed by plant shoots and roots. Both AgNPs and AgNO₃ could increase the soil redox potential and affect the growth and nutrient (N and phosphorus) uptake of plants. In soils with plants, there was no significant difference in denitrification rates and emissions of N₂O and CH₄ between control and AgNPs or AgNO₃ treatments at all tested concentrations (0.5, 1 and 10 mg kg^-1). However, low levels of AgNPs (0.5 mg kg^-1) significantly enhanced CO₂ emission throughout the experiment. Interestingly, in the absence of plants, a high dosage (10 mg kg^-1) of AgNPs generally inhibited soil denitrification and stimulated the emissions of CO₂, CH₄ and N₂O in the short-term. Meanwhile, the abundance of key denitrifying genes (nirS and nirK) was significantly increased by exposure to 10 mg kg^-1 AgNPs or AgNO₃. Our results suggest that emergent plants can alleviate the short-term negative effects of AgNPs on N and C cycling processes in wetland soils through different pathways.

Effects of nanofertilizers on soil and plant-associated microbial communities: Emerging trends and perspectives

Modern agricultural practices are relying excessively upon the use of synthetic fertilizers to supply essential nutrients to promote crop productivity. Though useful in the short term, their prolonged and persistent applications are harmful to soil fertility and nutrient dynamics of the rhizospheric microbiome. The application of nanotechnology in form of nanofertilizer provides an innovative, efficient, and eco-friendly alternative to synthetic fertilizers. The nanofertilizers allow a slow and sustained release of nutrients that not only supports plant growth but also conserve the diversity of the beneficial microbiome. Such attributes may help the phytomicrobiome to efficiently mitigate both biotic and abiotic stress conditions. Unfortunately, despite, exceptional efficiency and ease of applications, certain limitations are also associated with the nanofertilizers such as their complicated production process, tenuous transport and dosage-sensitive efficiency. These bottlenecks are causing a delay in the large-scale applications of nanofertilizers in agriculture. This review aims to highlight the current trends and perspectives on the use of nanofertilizers for improving soil fertility with a special focus on their effects on beneficial phyromicrobiome.

Enrofloxacin perturbs nitrogen transformation and assimilation in rice seedlings (Oryza sativa L.)

The extensive use of antibiotics worldwide has led to phytotoxicity and high risks to humans. Although research on the physiological toxicity of antibiotics is extensive, its influence on plant nitrogen uptake and assimilation remains unclear. The effect of enrofloxacin on nitrogen transformation and assimilation in rice (Oryza sativa L.) seedlings was investigated in this study. Enrofloxacin had no significant effect on rice growth, nitrogen assimilation and metabolism at low concentration, while significant changes were observed in high concentration. The growth of rice seedlings was inhibited, nitrate uptake was enhanced and nitrogen content increased significantly in both shoots and roots in enrofloxacin (800 μg L^-1) treatment. Furthermore, enrofloxacin promoted the activity of enzymes related to nitrogen assimilation, including nitrate reductase, nitrite reductase, glutamine synthetase, glutamate synthase, and glutamate dehydrogenase. High enzyme activity resulted in an increase in intermediate products and protein content, suggesting that rice seedlings may detoxify enrofloxacin stress through amino acid binding and nitro-oxidative stress might be one of the reasons of phenotype change. Gas chromatography-mass spectrometry results revealed that different types of metabolites in both shoots and roots increased with enrofloxacin stress. Specifically, glycine, serine, and threonine metabolism; aminoacyl-tRNA biosynthesis; alanine, aspartate, and glutamate metabolism; butanoate metabolism; glyoxylate and dicarboxylate metabolism in shoot; and tyrosine metabolism and citrate cycle in root were affected. Moreover, a significant correlation between nitrogen content, nitrogen assimilation enzyme activity, and metabolite content was observed. Collectively, these findings reveal the potential risks of using reclaimed wastewater irrigation and/or antibiotic-containing animal fertilizers on crops.

Enhanced antibacterial activity of acid treated MgO nanoparticles on Escherichia coli

Acid treatment is one of the effective methods that directly modifies surface physical and chemical properties of inorganic materials, which improves the materials' application potential. In this work, the surface modified MgO nanoparticles (NPs) were prepared through a facile acid-treatment method at room temperature. Compared with the untreated sample, the surviving Escherichia coli (E. coli, ATCC 25922) colonies of the modified MgO NPs decreased from 120 to 54 (10² CFU mL^-1). The enhanced antibacterial activity may be due to the improvement of oxygen vacancies and absorbed oxygen (O_A) content (from 41.6% to 63.1%) as confirmed by electron spin resonance (ESR) and X-ray photoelectron spectroscopy (XPS). These findings revealed that the acid treatment method could directly modify the surface of MgO NPs to expose more oxygen vacancies, which would promote reactive oxygen species (ROS) generation. The membrane tube and single ROS scavenging results further indicated that the increased antibacterial ability originated from the synergetic effect of ROS damage (especially ˙O₂ ^-) and direct contact between H-MgO NPs and E. coli.

MoS2 Nanosheets-Cyanobacteria Interaction: Reprogrammed Carbon and Nitrogen Metabolism

Fully understanding the environmental implications of engineered nanomaterials is crucial for their safe and sustainable use. Cyanobacteria, as the pioneers of the planet earth, play important roles in global carbon and nitrogen cycling. Here, we evaluated the biological effects of molybdenum disulfide (MoS₂) nanosheets on a N₂-fixation cyanobacteria (Nostoc sphaeroides) by monitoring growth and metabolome changes. MoS₂ nanosheets did not exert overt toxicity to Nostoc at the tested doses (0.1 and 1 mg/L). On the contrary, the intrinsic enzyme-like activities and semiconducting properties of MoS₂ nanosheets promoted the metabolic processes of Nostoc, including enhancing CO₂-fixation-related Calvin cycle metabolic pathway. Meanwhile, MoS₂ boosted the production of a range of biochemicals, including sugars, fatty acids, amino acids, and other valuable end products. The altered carbon metabolism subsequently drove proportional changes in nitrogen metabolism in Nostoc. These intracellular metabolic changes could potentially alter global C and N cycles. The findings of this study shed light on the nature and underlying mechanisms of bio-nanoparticle interactions, and offer the prospect of utilization bio-nanomaterials for efficient CO₂ sequestration and sustainable biochemical production.

Metabolomic Responses of Green Alga Chlamydomonas reinhardtii Exposed to Sublethal Concentrations of Inorganic and Methylmercury

Metabolomics characterizes low-molecular-weight molecules involved in different biochemical reactions and provides an integrated assessment of the physiological state of an organism. By using liquid chromatography-mass spectrometry targeted metabolomics, we examined the response of green alga Chlamydomonas reinhardtii to sublethal concentrations of inorganic mercury (IHg) and monomethylmercury (MeHg). We quantified the changes in the levels of 93 metabolites preselected based on the disturbed metabolic pathways obtained in a previous transcriptomics study. Metabolites are downstream products of the gene transcription; hence, metabolite quantification provided information about the biochemical status of the algal cells exposed to Hg compounds. The results showed that the alga adjusts its metabolism during 2 h exposure to 5 × 10^-9 and 5 × 10^-8 mol L^-1 IHg and MeHg by increasing the level of various metabolites involved in amino acid and nucleotide metabolism, photorespiration, and tricarboxylic acid (TCA) cycle, as well as the metabolism of fatty acids, carbohydrates, and antioxidants. Most of the metabolic perturbations in the alga were common for IHg and MeHg treatments. However, the exposure to IHg resulted in more pronounced perturbations in the fatty acid and TCA metabolism as compared with the exposure to MeHg. The observed metabolic perturbations were generally consistent with our previously published transcriptomics results for C. reinhardtii exposed to the comparable level of IHg and MeHg. The results highlight the potential of metabolomics for toxicity evaluation, especially to detect effects at an early stage of exposure prior to their physiological appearance.