Proteomics reveals surface electrical property-dependent toxic mechanisms of silver nanoparticles in Chlorella vulgaris

Cation-exchange fibers and silver nanoparticles-modified carbon electrodes for selective removal of hardness ions and simultaneous deactivation of microorganisms in capacitive deionization

The hardness and microorganism contamination are common problems of water quality around the world. Capacitive deionization (CDI) is a much-discussed solution to help solve the water crisis by providing efficient water softening while killing microorganism. Carboxylic (Na) cation-exchange fiber (CCEF) is an adsorbent material with good affinity for hardness ions. Silver nanoparticles (AgNPs) is a broad-spectrum microbicide. In this paper, the CCEF modified activated carbon (CCEF-AC) was used as cathode and showed excellent hardness ion adsorption selectivity at the optimum CCEF doping level (αCa2+/Na of 15.0, αMg2+/Na of 13.5). Its electrosorption capacity of Ca2+ reached 311 μmol/g, much higher than that of the AC cathode (188 μmol/g). It also showed good regenerable performance, retaining over 85 % of Ca2+ electrosorption capacity after 50 cycles stability test. The activated carbon modified with AgNPs (AC-Ag) was used as anode. When enhanced by an electric field, it could kill bacteria and microalgae with over 99 % and 90 % inhibition rates, respectively. This work has opened up a new way to simultaneously remove multiple pollutants (organic or inorganic) from water.

Utilizing proteomics to identify and optimize microalgae strains for high-quality dietary protein: a review

Algae-derived protein has immense potential to provide high-quality protein foods for the expanding human population. To meet its potential, a broad range of scientific tools are required to identify optimal algal strains from the hundreds of thousands available and identify ideal growing conditions for strains that produce high-quality protein with functional benefits. A research pipeline that includes proteomics can provide a deeper interpretation of microalgal composition and biochemistry in the pursuit of these goals. To date, proteomic investigations have largely focused on pathways that involve lipid production in selected microalgae species. Herein, we report the current state of microalgal proteome measurement and discuss promising approaches for the development of protein-containing food products derived from algae.

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.

The Occurrence of Oxidative Stress Induced by Silver Nanoparticles in Chlorella vulgaris Depends on the Surface-Stabilizing Agent

Silver nanoparticles (AgNPs) are of great interest due to their antimicrobial properties, but their reactivity and toxicity pose a significant risk to aquatic ecosystems. In biological systems, AgNPs tend to aggregate and dissolve, so they are often stabilized by agents that affect their physicochemical properties. In this study, microalga Chlorella vulgaris was used as a model organism to evaluate the effects of AgNPs in aquatic habitats. Algae were exposed to AgNPs stabilized with citrate and cetyltrimethylammonium bromide (CTAB) agents and to AgNO₃ at concentrations that allowed 75% cell survival after 72 h. To investigate algal response, silver accumulation, ROS content, damage to biomolecules (lipids, proteins, and DNA), activity of antioxidant enzymes (APX, PPX, CAT, SOD), content of non-enzymatic antioxidants (proline and GSH), and changes in ultrastructure were analyzed. The results showed that all treatments induced oxidative stress and adversely affected algal cells. AgNO₃ resulted in the fastest death of algae compared to both AgNPs, but the extent of oxidative damage and antioxidant enzymatic defense was similar to AgNP-citrate. Furthermore, AgNP-CTAB showed the least toxic effect and caused the least oxidative damage. These results highlight the importance of surface-stabilizing agents in determining the phytotoxicity of AgNPs and the underlying mechanisms affecting aquatic organisms.

Different responses of Chlorella vulgaris to silver nanoparticles and silver ions under modulation of nitric oxide

Silver nanoparticles (Ag-NPs) are widely used in daily life because of their antibacterial properties. A fraction of Ag-NPs are released into the ecosystem during their production and utilization. The toxicity of Ag-NPs has been reported. However, it is still disputed whether the toxicity is mainly due to the released silver ions (Ag⁺). In addition, few studies have reported the response of algae to metal nanoparticles under modulation of nitric oxide (NO). In this study, Chlorella vulgaris (C. vulgaris) was used as a model organism to study the toxic effects of Ag-NPs and Ag⁺ released from Ag-NPs on algae under the modulation of NO. The results showed that the biomass inhibition rate of Ag-NPs (44.84%) to C. vulgaris was higher than that of Ag⁺ (7.84%). Compared with Ag⁺, Ag-NPs induced more severe damage to photosynthetic pigments, photosynthetic system II (PSII) performance, and lipid peroxidation. More serious damage to cell permeability led to higher internalization of Ag under Ag-NPs stress. Application of exogenous NO reduced the inhibition ratio of photosynthetic pigments and chlorophyll autofluorescence. Further, NO reduced the MDA levels by scavenging reactive oxygen species induced by Ag-NPs. NO modulated the secretion of extracellular polymers and hampered the internalization of Ag. All these results showed that NO alleviates the toxicity of Ag-NPs to C. vulgaris. However, NO did not improve the toxic effects of Ag⁺. Our results provide new insights into the toxicity mechanism of Ag-NPs to algae modulated by the signal molecule NO.

Proteomic evaluation of nanotoxicity in aquatic organisms: A review

The alteration of organisms protein functions by engineered nanoparticles (ENPs) is dependent on the complex interplay between their inherent physicochemical properties (e.g., size, surface coating, shape) and environmental conditions (e.g., pH, organic matter). To date, there is increasing interest on the use of 'omics' approaches, such as proteomics, genomics, and others, to study ENPs-biomolecules interactions in aquatic organisms. However, although proteomics has recently been applied to investigate effects of ENPs and associated mechanisms in aquatic organisms, its use remain limited. Herein, proteomics techniques widely applied to investigate ENPs-protein interactions in aquatic organisms are reviewed. Data demonstrates that 2DE and mass spectrometry and/or their combination, thereof, are the most suitable techniques to elucidate ENPs-protein interactions. Furthermore, current status on ENPs and protein interactions, and possible mechanisms of nanotoxicity with emphasis on those that exert influence at protein expression levels, and key influencing factors on ENPs-proteins interactions are outlined. Most reported studies were done using synthetic media and essay protocols and had wide variability (not standardized); this may consequently limit data application in actual environmental systems. Therefore, there is a need for studies using realistic environmental concentrations of ENPs, and actual environmental matrixes (e.g., surface water) to aid better model development of ENPs-proteins interactions in aquatic systems.

Humic acids alleviate the toxicity of reduced graphene oxide modified by nanosized palladium in microalgae

The use of graphene-family materials modified by nanosized palladium (Pd/GFMs) has intensified rapidly in various fields; however, the effects of environmental factors (e.g., natural organic matter (NOM)) on the transformation and ecotoxicity of Pd/GFMs remain largely unknown. In this study, reduced graphene oxide modified by nanosized Pd (Pd/rGO) was incubated with humic acid (HA) under light irradiation for 56 d to explore the effects of NOM on the physicochemical transformations (e.g., defects, surface charges and dispersity) and biological toxicity (e.g., growth inhibition, oxidative stress and ultrastructural damage on algae cells) of Pd/GFMs. The results revealed that HA increased the defects and dispersity of Pd/rGO. Growth inhibition, damage to cellular ultrastructures, and oxidative stress in microalgae cells were induced by Pd/rGO, and corresponding defense responses (e.g., superoxide dismutase, peroxidase and glutathione) were activated. HA diminished the above defense responses in microalgae triggered by Pd/rGO by regulating GSH metabolism and the alanine biosynthesis pathway. In the presence of HA, cell wall damage (i.e., hole formation) caused by exposure to Pd/rGO was restored, and the plasmolysis area was reduced by 28.6 %. In addition, growth inhibition, lipid peroxidation, loss of mitochondrial membrane potential and ROS formation induced by 1.0 mg/L MoS₂NPs were decreased by 1.4-65.6 %, 13.9-26.1 %, 21.8-58.3 % and 9.6-16.1 %, respectively. These findings highlight the need to consider the effects of HA on the environmental transformation and biological toxicity of Pd/GFMs, which presents significant implications for the management of Pd/GFMs.

Building the Bridge From Aquatic Nanotoxicology to Safety by Design Silver Nanoparticles

Nanotechnologies have rapidly grown, and they are considered the new industrial revolution. However, the augmented production and wide applications of engineered nanomaterials (ENMs) and nanoparticles (NPs) inevitably lead to environmental exposure with consequences on human and environmental health. Engineered nanomaterial and nanoparticle (ENM/P) effects on humans and the environment are complex and largely depend on the interplay between their peculiar properties such as size, shape, coating, surface charge, and degree of agglomeration or aggregation and those of the receiving media/body. These rebounds on ENM/P safety and newly developed concepts such as the safety by design are gaining importance in the field of sustainable nanotechnologies. This article aims to review the critical characteristics of the ENM/Ps that need to be addressed in the safe by design process to develop ENM/Ps with the ablility to reduce/minimize any potential toxicological risks for living beings associated with their exposure. Specifically, we focused on silver nanoparticles (AgNPs) due to an increasing number of nanoproducts containing AgNPs, as well as an increasing knowledge about these nanomaterials (NMs) and their effects. We review the ecotoxicological effects documented on freshwater and marine species that demonstrate the importance of the relationship between the ENM/P design and their biological outcomes in terms of environmental safety.

Surface Coating-Modulated Phytotoxic Responses of Silver Nanoparticles in Plants and Freshwater Green Algae

Silver nanoparticles (AgNPs) have been implemented in a wide range of commercial products, resulting in their unregulated release into aquatic as well as terrestrial systems. This raises concerns over their impending environmental effects. Once released into the environment, they are prone to various transformation processes that modify their reactivity. In order to increase AgNP stability, different stabilizing coatings are applied during their synthesis. However, coating agents determine particle size and shape and influence their solubility, reactivity, and overall stability as well as their behavior and transformations in the biological medium. In this review, we attempt to give an overview on how the employment of different stabilizing coatings can modulate AgNP-induced phytotoxicity with respect to growth, physiology, and gene and protein expression in terrestrial and aquatic plants and freshwater algae.

Transcriptomics and Metabolomics Revealed the Biological Response of Chlorella pyrenoidesa to Single and Repeated Exposures of AgNPs at Different Concentrations

Increased release of engineered nanoparticles (ENPs) from widely used commercial products has threatened environmental health and safety, particularly the repeated exposures to ENPs with relatively low concentration. Herein, we studied the response of Chlorella pyrenoidesa (C. pyrenoidesa) to single and repeated exposures to silver nanoparticles (AgNPs). Repeated exposures to AgNPs promoted chlorophyll a and carotenoid production, and increased silver accumulation, thus enhancing the risk of AgNPs entering the food chain. Notably, the extracellular polymeric substances (EPS) content of the 1-AgNPs and 3-AgNPs groups were dramatically increased by 119.1% and 151.5%, respectively. We found that C. pyrenoidesa cells exposed to AgNPs had several significant alterations in metabolic process and cellular transcription. Most of the genes and metabolites are altered in a dose-dependent manner. Compared with the control group, single exposure had more differential genes and metabolites than repeated exposures. 562, 1341, 4014, 227, 483, and 2409 unigenes were differentially expressed by 1-0.5-AgNPs, 1-5-AgNPs, 1-10-AgNPs, 3-0.5-AgNPs, 3-5-AgNPs, and 3-10-AgNPs treatment groups compared with the control. Metabolomic analyses revealed that AgNPs altered the levels of sugars and amino acids, suggesting that AgNPs reprogrammed carbon/nitrogen metabolism. The changes of genes related to carbohydrate and amino acid metabolism, such as citrate synthase (CS), isocitrate dehydrogenase (IDH1), and malate dehydrogenase (MDH), further supported these results. These findings elucidated the mechanism of biological responses to repeated exposures to AgNPs, providing a new perspective on the risk assessment of nanomaterials.