Effects of CeO2, CuO, and ZnO nanoparticles on physiological features of Microcystis aeruginosa and the production and composition of extracellular polymeric substances

Extracellular polymers substances towards the toxicity effect of Microcystis flos-aquae under subjected to nanoplastic stress

The widespread presence of nanoplastics in aquatic ecosystems and their harmful effects on algae have garnered significant attention. However, little is known about the mechanisms of extracellular polymeric substances (EPS) derived from algae in response to nanoplastic stress. This study investigated the impact of EPS on the toxicity of polyvinyl chloride (PVC, 537 nm) and polymethyl methacrylate (PMMA, 485 nm) nanoplastics on Microcystis flos-aquae (MFa)under nanoplastic stress. The results revealed that EPS removal reduced algal biomass. PVC nanoplastics (250 mg L-1) caused biomass inhibition of -16.87% before and -9.82% after EPS removal. PMMA nanoparticles exhibited a more significant inhibition of growth and chlorophyll synthesis compared to PVC. After EPS removal, algal cells gradually recovered their maximum quantum yield of photosystem II and exhibited increased superoxide dismutase (SOD) enzyme activity, suggesting a self-regulation mechanism. Nanoplastic stress elevated EPS protein and polysaccharide levels, with maxima of 12.38 mg L-1 at 50 mg L-1 PVC and 17.24 mg L-1 at 100 mg L-1 PMMA. At the same time, the polysaccharide content in nanoplastics was significantly higher than that of proteins, with the maximum value being 2.82 times that of proteins. Fourier-transform infrared spectroscopy (FTIR) and excitation-emission matrix (EEM) analyses showed that aldehyde functional groups on the surface of algal cells were oxidized into carboxylic acids by both types of nanoparticles. Exposure to different nanoplastics increased humic-like substances in tightly bound EPS (TB-EPS), indicating that EPS dynamically adjusts to reduce nanoplastic toxicity by enhancing viscosity and algal aggregation. These results demonstrate that EPS mitigates the direct contact between algal cells and nanoplastics by increasing viscosity and promoting algal self-aggregation, thereby reducing the toxicity of nanoplastics to algae. This phenomenon is consistent across various stress conditions, providing valuable insights into the self-protection mechanisms of microalgae against nanoplastic stress.

Viscoelastic Fluid Focusing Chip-ICP-MS Single-Cell Analysis Enables Elucidating the Effect of Extracellular Polymeric Substances on Bioaccumulation of Hg2+/HgS in Microcystis aeruginosa Cell

Understanding the interactions between mercury and microalgae, especially the interactions between inorganic mercury (IHg) and extracellular polymeric substances (EPS, a protective barrier between cells and their external environment), is essential for elucidating mercury's toxicological mechanisms. Given the inherent cell heterogeneity, a novel analysis system of an online viscoelastic fluid focusing chip-time-resolved analysis inductively coupled plasma mass spectrometry has been developed to investigate the bioaccumulation of HgS nanoparticles and Hg2+ in single Microcystis aeruginosa (M. aeruginosa) cells, exploring the interaction mechanisms between HgS/Hg2+ accumulation in algal cells and EPS. The single-cell analysis results reveal minimal bioavailability of HgS within algal cells, with mercury's toxicity to M. aeruginosa being species-dependent. Notably, algal cells exhibited more heterogeneity in HgS uptake than in Hg2+ uptake. Under Hg2+/HgS stress, M. aeruginosa cells with EPS removed (EPS-R algal cells) showed an increased level of bioaccumulation of mercury compared to those with EPS (EPS-C algal cells), highlighting the critical role of EPS in mercury bioaccumulation. Overall, the designed viscoelastic fluid microfluidic focusing chip integrates focusing and cleaning functions, featuring easy fabrication, simple operation, low sample loss, and relatively high throughput. Under the optimal conditions, the sample throughput is 1195 min-1 and the cell recovery is 90%. Besides, this research offers novel insights into the interaction mechanisms between Hg2+/HgS and EPS in microalgal cells and unveils the specific toxic effects of Hg2+/HgS on M. aeruginosa at the single-cell level, contributing to a deeper understanding of mercury's ecological and toxicological impact in aquatic environments.

Effects of tire wear particle on growth, extracellular polymeric substance production and oxidation stress of algae Chlorella vulgaris: Performance and mechanism

Tire wear particles (TWP) represent a distinctive form of microplastics (MPs) that are widely distributed in aquatic ecosystems. However, the toxicity of various types of TWP on phytoplankton remain to be further explored. Thus, three different TWPs originating from replaced bicycle, car, and electro-mobile tire (marked as BTWP, CTWP, and ETWP) were selected and their long-term biological influences on Chlorella vulgaris were investigated. Results demonstrated TWPs showed a concentration-dependent growth promotion of Chlorella vulgaris, with a maximum promotion rate reached to 40.51 % (10 mg/L, 10 d), 23.5 % (80 mg/L, 12 d), and 28.7 % (20 mg/L, 12 d) in the presence of BTWP, CTWP and ETWP, respectively. Meanwhile, TWPs could stimulate the secretion of EPS and induce oxidative stress. EPS analysis revealed the increase of polysaccharides could protect the cell from the direct contact with TWP particles. Moreover, the increased concentration of EPS also helps to induce the settlement of TWP and reduce the leachate release. The release of TWP into the environment could act as an accelerator for the growth of Chlorella vulgaris, which might further change the normal physicochemical behaviors of algae colony in aquatic system. Our findings provide new insights into the toxicity mechanism of TWPs on freshwater algae and valuable data on environmental risk assessment of TWPs.

Influence of perfluorooctanoic acid on alkaline anaerobic fermentation of waste activated sludge: Perspective from volatile fatty acids production and sludge reduction

Alkaline anaerobic fermentation is an effective approach for resource utilization and reduction of waste activated sludge (WAS). Perfluorooctanoic acid (PFOA) is widespread in WAS, however, its potential impact on alkaline anaerobic fermentation of WAS remains largely unknown. Hence, this study focused on investigating the influence of PFOA on volatile fatty acids (VFAs) production and sludge reduction during alkaline anaerobic fermentation (pH = 10 ± 0.1), as well as the critical mechanisms. Results demonstrated that low PFOA concentration (5 mg/kg-TS) raised VFAs yield to 109.37%, while high levels of PFOA (25 and 50 mg/kg-TS) remarkably decreased VFAs production to 89.55% and 80.44% of the control. Mechanism exploration revealed that PFOA facilitated the solubilization process, and low PFOA level enhanced the accumulation of VFAs via increased bioavailable substrates and the activities of enzymes and microorganisms. On the contrary, high levels of PFOA were substantial biotoxicity, inducing excessive ROS production, causing oxidative damage, and reducing enzyme activity and functional microbial abundance, thereby decreasing VFAs production. Additionally, further analysis of sludge physicochemical properties confirmed that the effect of PFOA on WAS reduction exhibited the same trend as VFAs production. This work provides a basis for PFOA environmental risk assessment and WAS resource utilization.

Ferula latisecta gels for synthesis of zinc/silver binary nanoparticles: antibacterial effects against gram-negative and gram-positive bacteria and physicochemical characteristics

This study explores the potential antibacterial applications of zinc oxide nanoparticles (ZnO NPs) enhanced with silver (Ag) using plant gel (ZnO-AgO NPs). The problem addressed is the increasing prevalence of pathogenic bacteria and the need for new, effective antimicrobial agents. ZnO NPs possess distinctive physicochemical properties that enable them to selectively target bacterial cells. Their small size and high surface area-to-volume ratio allow efficient cellular uptake and interaction with bacterial cells. In this study, the average size of the synthesized ZnO-Ag nanoparticles was 77.1 nm, with a significant standard deviation of 33.7 nm, indicating a wide size distribution. The nanoparticles demonstrated remarkable antibacterial efficacy against gram-negative and gram-positive bacteria, with inhibition zones of 14.33 mm for E. coli and 15.66 mm for B. subtilis at a concentration of 300 µg/ml. Minimum inhibitory concentrations (MIC) were determined to be 100 µg/ml for E. coli and 75 µg/ml for S. saprophyticus. Additionally, ZnO-Ag NPs exhibited excellent biocompatibility, making them appropriate for various pharmacological uses. This study utilizes Ferula latisecta gels, offering a sustainable and eco-friendly approach to nanoparticle synthesis. Incorporating of Ag into ZnO NPs significantly enhances their antimicrobial properties, with the combined results showing great inhibition effects on pathogenic microbes. The findings suggest that ZnO-Ag NPs could be a promising candidate for addressing the challenges posed by drug-resistant bacterial infections and enhancing antimicrobial treatments.

Different biological responses of Skeletonema costatum and Prorocentrum donghaiense to polymetallic nodules from seawaters

The negative impacts of polymetallic nodules mining on deep-sea benthic organisms have been widely established, but there is still a lack of understanding of the environmental impact on the surface ocean scenario. Phytoplankton growth experiment was conducted to determine the biological effect of polymetallic nodules on Prorocentrum donghaiense and Skeletonema costatum. The results showed that regardless of concentration and particle size, polymetallic nodules show a promoting effect on P. donghaiense (p < 0.05), the cell density in the experimental group increased by 35.2%-46.5% compared to the control at the end of the experiment. While fine particles significantly inhibited the growth of S. costatum (p < 0.05), the maximum inhibition rate on cell density reached 63.1%. Polymetallic nodules significantly enhance the Fv/Fm and the maximum electron transport rate of photosystem II in P. donghaiense, thereby increasing its growth rate. However, polymetallic nodules particles stimulated the antioxidant activity and extracellular polymeric substances secretion of S. costatum, resulting in phytoplankton flocculation and sedimentation, which inhibits its growth. Thus, these discriminatory impacts may cause alterations in biomass and community structure, ultimately affecting the ecological function.

The Multifaceted Perspective on the Role of Green Synthesis of Nanoparticles in Promoting a Sustainable Green Economy

The current economic development paradigm, which is based on steadily rising resource consumption and pollution emissions, is no longer viable in a world with limited resources and ecological capacity. The “green economy” idea has presented this context with a chance to alter how society handles the interplay between the environmental and economic spheres. The related concept of “green nanotechnology” aims to use nano-innovations within the fields of materials science and engineering to generate products and processes that are economically and ecologically sustainable, enabling society to establish and preserve a green economy. Many different economic sectors are anticipated to be impacted by these applications, including those related to corrosion inhibitor nanofertilizers, nanoremediation, biodegradation, heavy metal detection, biofuel, insecticides and pesticides, and catalytic CO2 reduction. These innovations might make it possible to use non-traditional water sources safely and to create construction materials that are enabled by nanotechnology, improving living and ecological conditions. Therefore, our aim is to highlight how nanotechnology is being used in the green economy and to present promises for nano-applications in this domain. In the end, it emphasizes how critical it is to attain a truly sustainable advancement in nanotechnology.

Polystyrene microplastics enhanced the effect of PFOA on Chlorella sorokiniana: Perspective from the cellular and molecular levels

Microplastics (MPs) commonly coexist with other contaminants and alter their toxicity. Perfluorooctanoic acid (PFOA), an emerging pollutant, may interact with MPs but remain largely unknown about the joint toxicity of PFOA and MPs. Hence, this research explored the single and joint effects of PFOA and polystyrene microplastics (PS-MPs) on microalgae (Chlorella sorokiniana) at the cellular and molecular levels. Results demonstrated that PS-MPs increased PFOA bioavailability by altering cell membrane permeability, thus aggravating biotoxicity (synergistic effect). Meanwhile, the defense mechanisms (antioxidant system modulation and extracellular polymeric substances secretion) of Chlorella sorokiniana were activated to alleviate toxicity. Additionally, transcriptomic analysis illustrated that co-exposure had more differential expression genes (DEGs; 4379 DEGs) than single-exposure (PFOA: 2533 DEGs; PS-MPs: 492 DEGs), which were mainly distributed in the GO terms associated with the membrane composition and antioxidant system. The molecular regulatory network further revealed that PS-MPs and PFOA primarily regulated the response mechanisms of Chlorella sorokiniana by altering the ribosome biogenesis, photosynthesis, citrate cycle, oxidative stress, and antioxidant system (antioxidant enzyme, glutathione-ascorbate cycle). These findings elucidated that PS-MPs enhanced the effect of PFOA, providing new insights into the influences of MPs and PFOA on algae and the risk assessment of multiple contaminants. ENVIRONMENTAL IMPLICATION: MPs and PFAS, emerging contaminants, are difficult to degrade and pose a non-negligible threat to organisms. Co-pollution of MPs and PFAS is ubiquitous in the aquatic environment, while risks of co-existence to organisms remain unknown. The present study revealed the toxicity and defense mechanisms of microalgae exposure to PS-MPs and PFOA from cellular and molecular levels. According to biochemical and transcriptomic analyses, PS-MPs increased PFOA bioavailability and enhanced the effect of PFOA on Chlorella sorokiniana, showing a synergistic effect. This research provides a basis for assessing the eco-environmental risks of MPs and PFAS.

Toxic effects of aging mask microplastics on E. coli and dynamic changes in extracellular polymeric matter

Contamination of disposable medical masks has become a growing problem globally in the wake of Covid-19 due to their widespread use and improper disposal. Three different mask layers, namely the outer layer, the meltblown (MB) filler layer and the inner layers release three different types of microplastics, whose physical and chemical properties change after prolonged environmental weathering. In this study, physical and chemical changes of mask microplastics before and after aging were characterized by different characterization techniques. The toxic effect and mechanism of aged mask microplastics on Escherichia coli (E. coli) were studied by measuring the growth inhibition of mask microplastics, the change in ATPase activity, the change in malondialdehyde content and reactive oxygen species production, and the release of the chemical composition of exopolymeric substances (EPS). The microplastics of the aged MB filter layer had the most significant inhibitory effect on E. coli growth, reaching 19.2 % after 36 h. Also, under the influence of mask microplastics, ATPase activity of E. coli was inhibited and a large amount of EPS was released. The chemical composition of EPS has also changed. This study proposed the possible toxicity mechanism of mask microplastics and the self-protection mechanism of E. coli, and provided a reference for future research on the toxic effects of mask microplastics on environmental organisms.

A comparative study of the accumulation and detoxification of copper and zinc in Chlamydomonas reinhardtii: The role of extracellular polymeric substances

Extracellular polymeric substances (EPS) form an interface between microalgae and the surrounding water environment. Copper (Cu) and zinc (Zn) are essential micronutrients but may negatively affect microbial growth when their concentrations reach toxic thresholds. However, how EPS affect the accumulation and resistance of Cu and Zn in microalgae remains largely unknown. Here, we investigated EPS production upon Cu/Zn exposure and compared the tolerance strategies to the two metals by Chlamydomonas reinhardtii with and without EPS. Microalgal EPS synthesis was induced by Cu/Zn treatments, and the functional groups of polysaccharides and proteins were involved in complexation with metal ions. The extraction of EPS aggravated the toxicity and reduced the removal of metals from solution, but the effect was more pronounced for Cu than for Zn. Copper bound on the cell surface accounted for 54.6 ± 2.0 % of the Cu accumulated by C. reinhardtii, whose EPS components strongly correlated with Cu adsorption. In contrast, 74.3 ± 3.0 % of accumulated Zn was absorbed in cells, and glutathione synthesis was significantly induced. Redundancy and linear correlation analyses showed that the polysaccharide, protein and DNA contents in EPS were significantly correlated with Cu accumulation, absorption and adsorption but not with Zn. Data fitted to a Michaelis-Menten model further showed that the EPS-intact cells had higher binding capacity for Cu²⁺ but not for Zn²⁺. These differential impacts of EPS on Cu/Zn sorption and detoxification contribute to a more comprehensive understanding of the roles of microalgal EPS in the biogeochemical cycle of metals.

Changes of the physicochemical properties of extracellular polymeric substances (EPS) from Microcystis aeruginosa in response to microplastics

Microplastics (MPs) are ubiquitous in aquatic ecosystems and can significantly influence the growth, aggregation and functions of phytoplankton biomass. However, variations in the extracellular polymeric substances (EPS) of phytoplankton in terms of compositions and structures in response to MPs were still not reported. In this study, EPS matrix of Microsystis aeruginosa was applied and fractionated into loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) fractions, with the time-dependent changes in response to different concentrations (10, 100 and 500 mg/L) of MPs being explored via using the fluorescence excitation emission matrix coupled with parallel factor (EEM-PARAFAC) and two-dimensional Fourier transform infrared correlation spectroscopy (2D-FTIR-COS) analysis. Results showed that 500 mg/L of MP concentration significantly inhibited Microcystis growth by 30.5% but enhanced EPS secretion. In addition, organic composition in LB-EPS and TB-EPS varied differently in response to increased MP exposure, as the ratio of polysaccharide/protein increased in the TB-EPS but decreased in LB-EPS. Further analysis revealed obvious heterogeneities in organic component variations in response to MPs, as the C-O functional groups and glycosidic bonds in the TB-EPS preferentially responded, which lead to the domination of polysaccharides and humus substances; while the carbonyl, carboxyl and amino functional groups in the LB-EPS exhibited a preferential response, which caused the enhanced percentage of the tryptophan-like proteins. In addition to organic compositions, the aromaticity, hydrophobicity and humification in the LB-EPS fraction increased with enhanced MP exposure, which, as a result, may influence the ecotoxicological risk of MPs. Therefore, Microcystis can dynamically adjust not only the EPS contents but also the compositions in response to MPs exposure. The results can improve our understanding on the eco-physiological impact of phytoplankton-MP interaction in aquatic environment, and indicate that the dose-dependent and long-term effects of MPs on phytoplankton should be considered in future study.

Effect of Microplastics on the Removal of Nitrogen and Phosphorus from Synthetic Piggery Digestate by Microalgae

Microplastics (MPs) have been proven to be one of the major threats to the wastewater treatment system. However, the impact of MPs on microalgae-based wastewater treatment technology are still unknown. In this study, effects of polyvinyl chloride (PVC), polypropylene (PP), and polyethylene (PE) on the removal of nitrogen and phosphorus from synthetic piggery digestate by microalgae were investigated. Results show that the effect of PVC particle size on the growth of microalgae was significant. The effects of PVC content, PP particle size and content, PET particle size and content on the growth of microalgae were all not significant. The removal of ammonia nitrogen by microalgae was influenced significantly by PVC particle size and content, PP particle size and content, the effects of PET particle size and content on the removal of ammonia nitrogen were all not significant. The effects of particle size and content for three MPs on the removal of total phosphorus were all significant. Microalgae cells were bound together after being adsorbed by MPs, which increased the secretion of extracellular polymers and influenced the removal of ammonia nitrogen and total phosphorus.

ZnO nanoparticles interfere with top-down effect of the protozoan paramecium on removing microcystis

Under intensive human activity, sewage discharge causes eutrophication-driven cyanobacteria blooms as well as nanomaterial pollution. In biological control of harmful cyanobacteria, top-down effect of protozoan has great potentials for removing cyanobacterial populations, degrading cyanotoxins, and improving phytoplankton community. ZnO nanoparticles as a kind of emerging contaminants have attracted increasing attention because of wide application and their high bio-toxicity effects on reducing the ingestion of aquatic animals including Paramecium, thereby possibly disturbing top-down control of cyanobacteria. Therefore, this study investigated the effects of ZnO nanoparticles at environmental-relevant concentrations on the protozoan Paramecium removing toxic Microcystis. Results showed Paramecium effectively eliminated all the Microcystis, despite exposure to ZnO nanoparticles. However, their ingestion rate was significantly reduced at more than 0.1 mg L^-1 ZnO nanoparticles, thereby delaying Microcystis removal. Nevertheless, at 0.1 mg L^-1 ZnO nanoparticles, the time to Microcystis extinction decreased compared to the group without ZnO nanoparticles, because Microcystis populations were reduced under this circumstance, while ingestion rate of Paramecium was unaffected. Furthermore, ZnO nanoparticles obviously accumulated in food vacuoles of Paramecium, and the size of nanoparticles aggregates and zinc concentrations in Paramecium were increased with ZnO nanoparticles concentrations. At the end of experiment, these food vacuoles were not dissipated. Overall, these findings suggest that ZnO nanoparticles impair protozoan top-down effects through reducing Microcystis and ingestion rate as well as disturbing functions of their digestive organelles, and highlight the need to consider the interfering effects of environmental pollutants on cyanobacterial removal efficiency by protozoans in natural waters.

Nanomaterials for biogas augmentation towards renewable and sustainable energy production: A critical review

Nanotechnology is considered one of the most significant advancements in science and technology over the last few decades. However, the contemporary use of nanomaterials in bioenergy production is very deficient. This study evaluates the application of nanomaterials for biogas production from different kinds of waste. A state-of-the-art comprehensive review is carried out to elaborate on the deployment of different categories of nano-additives (metal oxides, zero-valent metals, various compounds, carbon-based nanomaterials, nano-composites, and nano-ash) in several kinds of biodegradable waste, including cattle manure, wastewater sludge, municipal solid waste, lake sediments, and sanitary landfills. This study discusses the pros and cons of nano-additives on biogas production from the anaerobic digestion process. Several all-inclusive tables are presented to appraise the literature on different nanomaterials used for biogas production from biomass. Future perspectives to increase biogas production via nano-additives are presented, and the conclusion is drawn on the productivity of biogas based on various nanomaterials. A qualitative review of relevant literature published in the last 50 years is conducted using the bibliometric technique for the first time in literature. About 14,000 research articles are included in this analysis, indexed on the Web of Science. The analysis revealed that the last decade (2010–20) was the golden era for biogas literature, as 84.4% of total publications were published in this timeline. Moreover, it was observed that nanomaterials had revolutionized the field of anaerobic digestion, methane production, and waste activated sludge; and are currently the central pivot of the research community. The toxicity of nanomaterials adversely affects anaerobic bacteria; therefore, using bioactive nanomaterials is emerging as the best alternative. Conducting optimization studies by varying substrate and nanomaterials’ size, concentration and shape is still a field. Furthermore, collecting and disposing nanomaterials at the end of the anaerobic process is a critical environmental challenge to technology implementation that needs to be addressed before the nanomaterials assisted anaerobic process could pave its path to the large-scale industrial sector.

Combined Effect of NZVI and H2O2 on the Cyanobacterium Microcystis aeruginosa: Performance and Mechanism

In order to eliminate the harmful cyanobacterium Microcystis aeruginosa and the algal organic matters (AOMs) produced by M. aeruginosa, the combined process of nanoscale zero-valent iron (NZVI) and hydrogen peroxide (H₂O₂) has been carried out, and the removal mechanism has also been clarified. As the initial cyanobacterial cell concentration is 1.0 (±0.05) × 10⁵ cells·mL^-1, all the treatments of NZVI, H₂O₂, and NZVI/H₂O₂ have inhibition effects on both the Chl a contents and photosynthetic pigments, with the Chl a removal efficiency of 47.3%, 80.5%, and 90.7% on the 5th day, respectively; moreover, the variation of ζ potential is proportional to that of the Chl a removal efficiency. The malondialdehyde content and superoxide dismutase activity are firstly increased and ultimately decreased to mitigate the oxidative stress under all the treatments. Compared with NZVI treatment alone, the oxidation of the H₂O₂ and NZVI/H₂O₂ processes can effectively destroy the antioxidant enzyme system and then inactivate the cyanobacterial cells, which further leads to the release of photosynthetic pigments and intracellular organic matters (IOM); in addition, the IOM removal efficiency (in terms of TOC) is 61.3% and 54.1% for the H₂O₂ and NZVI/H₂O₂ processes, respectively. Although NZVI is much more effective for extracellular organic matters (EOM) removal, it is less effective for IOM removal. The results of the three-dimensional EEM fluorescence spectra analysis further confirm that both H₂O₂ and NZVI/H₂O₂ have the ability to remove fluorescent substances from EOM and IOM, due to the oxidation mechanism; while NZVI has no removal effect for the fluorescent substances from EOM, it can remove part of fluorescent substances from IOM due to the agglomeration. All the results demonstrate that the NZVI/H₂O₂ process is a highly effective and applicable technology for the removal of M. aeruginosa and AOMs.

Aquatic organisms modulate the bioreactivity of engineered nanoparticles: focus on biomolecular corona

The increased use of nanoparticle (NP)-enabled materials in everyday-life products have raised concerns about their environmental implications and safety. This motivated the extensive research in nanoecotoxicology showing the possibility that NPs could cause harm to the aquatic organisms if present at high concentrations. By contrast, studies dealing with influence that organisms could exert on the fate and thus effects of NPs are still very rare. Drawing on the existing up-to-date knowledge we critically discuss the formation of biomolecular corona as one of the mechanisms by which organisms exerted control on the NPs fate in the aquatic and biotic environments. We focused the formation of corona by exogeneous and endogenous biomolecules and illustrated the discussion with the specific example of phytoplankton and aquatic invertebrate species. We highlighted the necessity to incorporate the concept of biomolecular corona within more general framework considering the feedback of aquatic organisms and the control they exert in shaping the fate and impact of NPs in the aquatic and biological environment. In our view such broader perspective will contribute to get novel insights into the drivers of environmental transformations of NPs and their mechanisms, which are important in environmental risk assessment.

Toxicity mechanism of cerium oxide nanoparticles on cyanobacteria Microcystis aeruginosa and their ecological risks

The extensive application of cerium oxide nanoparticles (CeO₂ NPs), a type of rare earth nanomaterial, led to pollution into aquatic environments. Cyanobacteria, a significant component of freshwater ecosystems, can interact with CeO₂ NPs. However, little attention has been paid as to whether CeO₂ NPs will have adverse effects on cyanobacteria. In the present study, Microcystis aeruginosa (FACHB-942) was exposed to different concentrations (0, 1, 10, and 50 mg/L) of CeO₂ NPs. Results showed 50 mg/L CeO₂ NPs inhibited algal growth (11.48% ± 5.76%), suppressed photosynthesis and induced the generation of reactive oxygen species (ROS) after 72 h exposure. The toxicity mechanism is the adsorption of CeO₂ NPs on cell surface, the ROS formation and the intracellular Ce. Additionally, the intracellular microcystins (MCs) content was significantly induced (11.84% ± 1.47%) by 50 mg/L CeO₂ NPs, while no significance was found in 1 and 10 mg/L CeO₂ NP treatments. Results indicated high concentrations of CeO₂ NPs could be toxic to algae through the adverse effects on algal growth and photosynthesis. Moreover, the promoted MCs production could also pose a threat to freshwater ecosystems due to the possible release into the environment.

Enhanced production of microalgae-originated photosensitizer by integrating photosynthetic electrons extraction and antibiotic induction towards photocatalytic degradation of antibiotic: A novel complementary treatment process for antibiotic removal from effluent of conventional biological wastewater treatment

Antibiotic residues in effluents from bio-treated wastewaters are mainly responsible for the spread of antibiotic resistance genes in the environment. Conventional physicochemical treatments are thought to be unsustainable due to high energy consumption, large consumption of chemicals and environmental unfriendly processing step. In this study, a novel approach by integrating photosynthetic electrons extraction from microalgae with antibiotic induction was used to enhance the production of microalgae-originated photosensitizer for photolytic removal of antibiotic residues in effluents from conventional bio-treated wastewaters. Results showed that the accumulation of photoactive substances in extracellular polymeric substance (EPS) of chlorella vulgaris was positively related to the amounts of photosynthetic electrons extracted by the electrode which is a potential-dependent process and can be further enhanced by tetracycline (TC) induction. The protein and humic acid which are considered two main photoactive substances in EPS produced at 0.6 V accumulated to a high level of 320 and 24 μg/cm³ and were further increased to 380 and 48 μg/cm³ when TC was added which were 4.7 and 6.4-folds higher than that produced at potential free in the absence of TC. The EPS produced at 0.6 and 0.8 V led to 1.34 and 1.53-fold acceleration in photosensitized degradation of TC compared to that of EPS free in secondary effluent of municipal wastewater treatment plant. The complex heterocyclic ring structure of TC was broken down into simple monocyclic aromatic compounds, indicating a marked reduction in biotoxicity and recalcitrance. The hydroxyl radical played a main role for the photolysis of TC followed by singlet oxygen. This technology provides a new alternative to conventional physicochemical treatment as complementary treatment processes for biological wastewater treatment in terms of antibiotics removal.

Copper Tolerance Mechanism of the Novel Marine Multi-Stress Tolerant Yeast Meyerozyma guilliermondii GXDK6 as Revealed by Integrated Omics Analysis

Various agricultural products used in food fermentation are polluted by heavy metals, especially copper, which seriously endangers human health. Methods to remove copper with microbial strategies have gained interests. A novel Meyerozyma guilliermondii GXDK6 could survive independently under high stress of copper (1400 ppm). The copper tolerance mechanism of GXDK6 was revealed by integrated omics in this work. Whole-genome analysis showed that nine genes (i.e., CCC2, CTR3, FRE2, GGT, GST, CAT, SOD2, PXMP4, and HSP82) were related to GXDK6 copper tolerance. Copper stress elevated glutathione metabolism-related gene expression, glutathione content, and glutathione sulfur transferase activity, suggesting enhanced copper conjugation and detoxification in cells. The inhibited copper uptake by Ctr3 and enhanced copper efflux by Ccc2 contributed to the decrease in intracellular copper concentration. The improved expression of antioxidant enzyme genes (PXMP4, SOD2, and CAT), accompanied by the enhanced activities of antioxidant enzymes (peroxidase, superoxide dismutase, and catalase), decreased copper-induced reactive oxygen species production, protein carbonylation, lipid peroxidation, and cell death. The metabolite D-mannose against harsh stress conditions was beneficial to improving copper tolerance. This study contributed to understanding the copper tolerance mechanism of M. guilliermondii and its application in removing copper during fermentation.

Phycoremediation mechanisms of heavy metals using living green microalgae: physicochemical and molecular approaches for enhancing selectivity and removal capacity

Heavy metal (HM) contamination of water bodies is a serious global environmental problem. Because they are not biodegradable, they can accumulate in food chains, causing various signs of toxicity to exposed organisms, including humans. Due to its effectiveness, low cost, and ecological aspect, phycoremediation, or the use of microalgae's ecological functions in the treatment of HMs contaminated wastewater, is one of the most recommended processes. This study aims to examine in depth the mechanisms involved in the phycoremediation of HMs by microalgae, it also provides an overview of the prospects for improving the productivity, selectivity, and cost-effectiveness of this bioprocess through physicochemical and genetic engineering applications. Firstly, this review proposes a detailed examination of the biosorption interactions between cell wall functional groups and HMs, and their complexation with extracellular polymeric substances released by microalgae in the extracellular environment under stress conditions. Subsequently, the metal transporters involved in the intracellular bioaccumulation of HMs as well as the main intracellular mechanisms including compartmentalization in cell organelles, enzymatic biotransformation, or photoreduction of HMs were also extensively reviewed. In the last section, future perspectives of physicochemical and genetic approaches that could be used to improve the phytoremediation process in terms of removal efficiency, selectivity for a targeted metal, or reduction of treatment time and cost are discussed, which paves the way for large-scale application of phytoremediation processes.

Contrasting detoxification mechanisms of Chlamydomonas reinhardtii under Cd and Pb stress

Chlamydomonas reinhardtii has been frequently investigated for its resistance to metals; however, few studies have systematically compared the intracellular and extracellular processes involved in the detoxification of Cd and Pb by this microalga. We found that C. reinhardtii was more tolerant to Pb (concentration for 50% of the maximal effect; EC50: 29.48 ± 8.83 mg L^-1) than to Cd (EC50: 12.48 ± 1.30 mg L^-1) after 96 h of exposure. Extracellular polymeric substances (EPS), intracellular starch granules, lipid droplets, and glutathione were significantly increased under Cd and Pb treatments. Lead-containing particles were formed outside of the cells exposed to 30 mg L^-1 of Pb, whereas no minerals were present when Cd was added. Various EPS functional groups, including -COOH, C-O-C (polysaccharides), and amide I and II (proteins), were involved in the interactions with Cd and Pb. The Pb removal rate (60.46-78.27%) by C. reinhardtii was higher than that of Cd (50.61-59.38%), and the microalgal cells with intact EPS bound more metals than those without EPS. Adsorption accounted for 79.62% of the total Cd accumulation in the low-Cd treatment, whereas absorption dominated the Pb accumulation at low Pb concentrations. The distributions of Cd and Pb in and out of the microalgal cells were reversed when the concentrations of the two metals increased. The detoxification strategies of C. reinhardtii for Cd and Pb were completely different, and these findings may assist in the phycoremediation of metal pollution in aquatic environments.

Graphene-Based Nanomaterials Modulate Internal Biofilm Interactions and Microbial Diversity

Graphene-based nanomaterials (GBMs), such as graphene oxide (GO) and reduced graphene oxide (rGO), possess unique properties triggering high expectations for the development of new technological applications and are forecasted to be produced at industrial-scale. This raises the question of potential adverse outcomes on living organisms and especially toward microorganisms constituting the basis of the trophic chain in ecosystems. However, investigations on GBMs toxicity were performed on various microorganisms using single species that are helpful to determine toxicity mechanisms but fail to predict the consequences of the observed effects at a larger organization scale. Thus, this study focuses on the ecotoxicological assessment of GO and rGO toward a biofilm composed of the diatom Nitzschia palea associated to a bacterial consortium. After 48 and 144 h of exposure to these GBMs at 0, 0.1, 1, and 10 mg.L⁻¹, their effects on the diatom physiology, the structure, and the metabolism of bacterial communities were measured through the use of flow cytometry, 16S amplicon sequencing, and Biolog ecoplates, respectively. The exposure to both of these GBMs stimulated the diatom growth. Besides, GO exerted strong bacterial growth inhibition as from 1 mg.L⁻¹, influenced the taxonomic composition of diatom-associated bacterial consortium, and increased transiently the bacterial activity related to carbon cycling, with weak toxicity toward the diatom. On the contrary, rGO was shown to exert a weaker toxicity toward the bacterial consortium, whereas it influenced more strongly the diatom physiology. When compared to the results from the literature using single species tests, our study suggests that diatoms benefited from diatom-bacteria interactions and that the biofilm was able to maintain or recover its carbon-related metabolic activities when exposed to GBMs.

Biosorption behavior and mechanism of cadmium from aqueous solutions by Synechocystis sp. PCC6803

Cyanobacteria are promising adsorbents that are widely used for heavy metal removal in aqueous solutions. However, the underlying adsorption mechanism of Synechocystis sp. PCC6803 is currently unclear. In this study, the adsorption behavior and mechanism of cadmium (Cd²⁺) were investigated. Batch biosorption experiments showed that the optimal adsorption conditions were pH 7.0, 30 °C, 15 min, and an initial ion concentration of 4.0 mg L⁻¹. The adsorption process fitted well with the pseudo-second order kinetic model, mainly based on chemisorption. Complexation of Cd²⁺ with carboxyl, hydroxyl, carbonyl, and amido groups was demonstrated by Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectrometry (EDX) analyses confirmed the presence of Cd²⁺ on the cyanobacterial cell surface and intracellularly. Cd²⁺ could lead to reactive oxygen species (ROS) accumulation and photosynthesis inhibition in cyanobacterial cells, and glutathione (GSH) played an important role in alleviating Cd²⁺ toxicity. Analyses of three-dimensional fluorescence spectroscopy (3D-EEM) and high performance anion exchange chromatography-pulsed amperometric detection (HPAEC-PAD) revealed the changes of the composition and content of EPS after Cd²⁺ adsorption, respectively. Real-time quantitative polymerase chain reaction (RT-qPCR) revealed the potential molecular regulatory mechanisms involved in Cd²⁺ biosorption. These results revealed the adsorption mechanism of Cd²⁺ by Synechocystis sp. PCC6803 and provided theoretical guidance for insight into the biosorption mechanisms of heavy metals by other strains.

The results of extracellular polymeric substances (EPS) extraction, physiological and biochemical determination and gene expression revealed the adsorption mechanism of Synechocystis sp. PCC6803 under cadmium stress.

Effective inactivation of Microcystis aeruginosa by a novel Z-scheme composite photocatalyst under visible light irradiation

Microcystis aeruginosa is one of the most famous harmful algae. In this work, Z-scheme g-C₃N₄-MoO₃ (Mo-CN) composite photocatalysts were successfully synthesized to alleviate the algae pollution. The obtained composites exhibited excellent performance for the inactivation of M. aeruginosa. The optimal photocatalysts (15Mo-CN) achieved a removal efficiency of 97% for the algal cells after 3 h visible light irradiation, which was attributed to their remarkable surface properties and ingenious structure design. The physiological status of Microcystis aeruginosa were evaluated by the chlorophyll a (chla), relative electron transport rate (rETR) and maximum photochemical efficiency (Fv/Fm), and all of them decreased in different degrees. Furthermore, the as-prepared photocatalysts also show a certain activity for the removal of leaked macromolecule organic compounds during the process of algal cells inactivation. Finally, a possible mechanism on the photocatalytic inactivation of algal cells by the Z-scheme photocatalysts was deduced based on the experimental and characterization results. We believe this study would provide new insights into the development of promising technology and basic theory for remediation of algae pollution.

Cadmium Selenide Formation Influences the Production and Characteristics of Extracellular Polymeric Substances of Anaerobic Granular Sludge

Feeding cadmium (II) and selenium (IV) simultaneously to anaerobic granular sludge with the aim of synthesizing cadmium selenide (CdSe) nanoparticles induces compositional changes in the extracellular polymeric substances (EPS) matrix of this sludge. A methanogenic anaerobic granular sludge was repeatedly exposed to Cd(II) (10-50 mg L^-1) and selenite (79 mg L^-1) for 300 days at pH 7.3 and 30 °C in a fed-batch feeding regime for enrichment of Se-reducing bacteria and synthesis of CdSe nanoparticles. EPS fingerprints of the granular sludge, obtained by size exclusion chromatography coupled to a fluorescence detector, showed a significant increase in the intensity of protein-like substances with > 100 kDa apparent molecular weight (aMW) upon repeated exposure to Cd(II) and Se(VI). This was accompanied by a prominent decrease in protein-like substances of aMW < 10 kDa. The fingerprint of the humic-like substances showed emergence of a new peak with aMW of 13 to 300 kDa in the EPS extracted from the Cd/Se fed granular sludge. Experiments on metal(loid)-EPS interactions showed that the CdSe nanoparticles interact mainly with loosely bound EPS (LB-EPS). This study showed that the formation of Se(0) and CdSe nanoparticles occurs in the LB-EPS fraction of the granular sludge and repeated exposure to Cd and Se induces compositional changes in the EPS matrix.

The Crucial Role of Environmental Coronas in Determining the Biological Effects of Engineered Nanomaterials

In aquatic environments, a large number of ecological macromolecules (e.g., natural organic matter (NOM), extracellular polymeric substances (EPS), and proteins) can adsorb onto the surface of engineered nanomaterials (ENMs) to form a unique environmental corona. The presence of environmental corona as an eco-nano interface can significantly alter the bioavailability, biocompatibility, and toxicity of pristine ENMs to aquatic organisms. However, as an emerging field, research on the impact of the environmental corona on the fate and behavior of ENMs in aquatic environments is still in its infancy. To promote a deeper understanding of its importance in driving or moderating ENM toxicity, this study systemically recapitulates the literature of representative types of macromolecules that are adsorbed onto ENMs; these constitute the environmental corona, including NOM, EPS, proteins, and surfactants. Next, the ecotoxicological effects of environmental corona-coated ENMs on representative aquatic organisms at different trophic levels are discussed in comparison to pristine ENMs, based on the reported studies. According to this analysis, molecular mechanisms triggered by pristine and environmental corona-coated ENMs are compared, including membrane adhesion, membrane damage, cellular internalization, oxidative stress, immunotoxicity, genotoxicity, and reproductive toxicity. Finally, current knowledge gaps and challenges in this field are discussed from the ecotoxicology perspective.

The Role of Cyanobacterial External Layers in Mass Transfer: Evidence from Temperature Shock Experiments by Noninvasive Microtest Technology

Groundwork on cyanobacterial external layers is crucial for an improved understanding of the persistent dominance of cyanobacteria in freshwaters. In this study, the role of two morphotypes of external layers in Microcystis and Nostoc in mass transfer and instantaneous temperature shock were explored by noninvasive microtest technology (NMT) after a series of pretreatments, to obtain the external layers retained or stripped samples. The results showed no statistical influence on photosynthetic activity between retained and stripped samples in both Microcystis and Nostoc. External-layer-retaining strains had higher net O₂ effluxes than stripped strains. Moreover, the net NH₄⁺ influx was significantly higher for the sheath retaining Nostoc than for the stripped sample, indicating that external layers might be an important feature driving mass transfer in cyanobacteria. However, the role of slime in NH₄⁺ absorption was limited compared with that of sheath. In addition, external-layer-retaining strains exhibited a longer response time to instantaneous temperature shock, greater net O₂ effluxes at a 4 °C shock and lower net O₂ influx at a 35 °C shock, which were interpreted as reflecting a tolerance to temperature fluctuation over short time scales via a buffer function of external layers to stabilize cell activity, ameliorating the efficiency of photosynthesis and respiration. These results advance current knowledge regarding the external layers, especially the dense sheath, involved in the mass transfer in cyanobacteria, and provide new clues concerning the adaptive strategies of cyanobacteria under global climate changes.

Behavior and Mechanism of Cesium Biosorption from Aqueous Solution by Living Synechococcus PCC7002

Many efforts have focused on the adsorption of metals from contaminated water by microbes. Synechococcus PCC7002, a major marine cyanobacteria, is widely applied to remove metals from the ocean's photic zone. However, its ability to adsorb cesium (Cs) nuclides has received little attention. In this study, the biosorption behavior of Cs(I) from ultrapure distilled water by living Synechococcus PCC7002 was investigated based on kinetic and isotherm studies, and the biosorption mechanism was characterized by Fourier-transform infrared spectroscopy, Raman&nbsp;spectroscopy, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectrometry, and three-dimensional excitation emission matrix fluorescence spectroscopy. Synechococcus PCC7002 showed extremely high tolerance to Cs ions and its minimal inhibitory concentration was 8.6 g/L. Extracellular polymeric substances (EPS) in Synechococcus PCC7002 played a vital role in this tolerance. The biosorption of Cs by Synechococcus PCC7002 conformed to a Freundlich-type isotherm model and pseudo-second-order kinetics. The binding of Cs(I) was primarily attributed to the extracellular proteins in EPS, with the amino, hydroxyl, and phosphate groups on the cell walls contributing to Cs adsorption. The biosorption of Cs involved two mechanisms: Passive adsorption on the cell surface at low Cs concentrations and active intracellular adsorption at high Cs concentrations. The results demonstrate that the behavior and mechanism of Cs adsorption by Synechococcus PCC7002 differ based on the Cs ions concentration.

Antimicrobial Nanostructured Coatings: A Gas Phase Deposition and Magnetron Sputtering Perspective

Counteracting the spreading of multi-drug-resistant pathogens, taking place through surface-mediated cross-contamination, is amongst the higher priorities in public health policies. For these reason an appropriate design of antimicrobial nanostructured coatings may allow to exploit different antimicrobial mechanisms pathways, to be specifically activated by tailoring the coatings composition and morphology. Furthermore, their mechanical properties are of the utmost importance in view of the antimicrobial surface durability. Indeed, the coating properties might be tuned differently according to the specific synthesis method. The present review focuses on nanoparticle based bactericidal coatings obtained via magneton-spattering and supersonic cluster beam deposition. The bacteria–NP interaction mechanisms are first reviewed, thus making clear the requirements that a nanoparticle-based film should meet in order to serve as a bactericidal coating. Paradigmatic examples of coatings, obtained by magnetron sputtering and supersonic cluster beam deposition, are discussed. The emphasis is on widening the bactericidal spectrum so as to be effective both against gram-positive and gram-negative bacteria, while ensuring a good adhesion to a variety of substrates and mechanical durability. It is discussed how this goal may be achieved combining different elements into the coating.

Assessment of membrane bioreactor fouling with the addition of suspended aluminum nitride nanoparticles

In this study, we assessed fouling in a membrane bioreactor (MBR) with the addition of suspended aluminum nitride (AlN) nanoparticles (NPs). Three parallel laboratory-scale submerged MBRs were operated with 0, 10, and 50 mg AlN NPs/L for over 70 days. The results showed that the addition of suspended AlN NPs did not significantly affect pollutant biodegradation; there was only a slight decrease in NH₄⁺-N removal. Furthermore, the membrane's permeability was increased with effective fouling mitigation by the addition of a high amount of suspended AlN NPs. This was because the suspended AlN NPs decreased the content of polysaccharides in both the extracellular polymeric substances and soluble microbial products, and decreased the sludge floc size. However, the AlN NPs also promoted pore-blocking, particularly standard blocking, which enhanced irreversible fouling. Additionally, owing to the larger ionic radius and higher electronegativity, the AlN NPs inhibited the accumulation of framework components (SiO₂). Therefore, suspended AlN NPs resulted in a thinner cake layer.

Physicochemical and Biological Effects on Activated Sludge Performance and Activity Recovery of Damaged Sludge by Exposure to CeO2 Nanoparticles in Sequencing Batch Reactors

Recently, the growing release of CeO₂ nanoparticles (CeO₂ NPs) into sewage systems has attracted great concern. Several studies have extensively explored CeO₂ NPs' potential adverse impacts on wastewater treatment plants; however, the impaired activated sludge recovery potentials have seldom been addressed to date. To explore the physicochemical and biological effects on the activated sludge performance and activity recovery of damaged sludge by exposure to CeO₂ NPs in sequencing batch reactors (SBRs), four reactors and multiple indicators including water quality, key enzymes, microbial metabolites, the microbial community structure and toxicity were used. Results showed that 10-week exposure to higher CeO₂ NP concentration (1, 10 mg/L) resulted in a sharp decrease in nitrogen and phosphorus removal efficiencies, which were consistent with the tendencies of key enzymes. Meanwhile, CeO₂ NPs at concentrations of 0.1, 1, and 10 mg/L decreased the secretion of tightly bound extracellular polymeric substances to 0.13%, 3.14%, and 28.60%, respectively, compared to the control. In addition, two-week recovery period assays revealed that the functional bacteria Proteobacteria, Nitrospirae and Planctomycetes recovered slightly at the phyla level, as analyzed through high-throughput sequencing, which was consistent with the small amount of improvement of the effluent performance of the system. This reflected the small possibility of the activity recovery of damaged sludge.

Effects of different types of extracellular polysaccharides isolated from cyanobacterial blooms on the colony formation of unicellular Microcystis aeruginosa

In this study, two types of extracellular polysaccharides (EPS), namely, mixed EPS (MX-EPS) and tightly bound EPS (TB-EPS), were extracted from cyanobacterial blooms using different methods. To evaluate their compositional differences, elemental composition, FTIR, and TG/DTA profile were measured for both EPS samples. Following that, unicellular Microcystis aeruginosa was cultured in a medium containing EPS, Ca²⁺ ion, and Mg²⁺ ion, and the effect of each type of EPS on the colony formation of M. aeruginosa was examined. Results showed that TB-EPS had more carboxy groups than MX-EPS, and that the TB-EPS medium contained Ca²⁺ and Mg²⁺ ions. These cations were not detected in the MX-EPS medium. During the colony formation experiment, colonies were observed when Ca²⁺ and Mg²⁺ ions were present at 250 mg/L concentration each. In addition, colony density increased when TB-EPS was added, compared to that of MX-EPS. Colonies were also observed in the medium containing only TB-EPS (100 mg/L), indicating that M. aeruginosa can form colonies using Ca²⁺ ion present in TB-EPS. During the MX-EPS extraction, Ca²⁺ ion chelated with EDTA was removed during ethanol precipitation. Therefore, the extraction protocol followed for TB-EPS was better than that of MX-EPS for maintaining Ca²⁺ ions, and thereby maintaining an EPS composition that enables for colony formation.

Influence of extracellular polymeric substances on cell-NPs heteroaggregation process and toxicity of cerium dioxide NPs to Microcystis aeruginosa

The presence of abundant extracellular polymeric substances (EPS) play a vital role in affecting heteroaggregation process and toxicity of nanoparticles (NPs) to Microcystis aeruginosa. Interactions between n-CeO₂ and cyanobacteria with/without EPS and the toxicity of n-CeO₂ to M. aeruginosa were investigated in this study. Aggregation kinetics of n-CeO₂ under both soluble EPS (SEPS) and bound EPS (BEPS) indicated the presence of EPS could induced the formation of EPS-NPs aggregates. Heteroaggregation between cells and n-CeO₂ was confirmed through co-settling experiment and SEM-EDS observation. SEPS contributed to the observable heteroaggregation using spectral measurement. Heteroaggregation between cells and n-CeO2 under no BEPS was hardly obtained through spectral measurement, but SEM-EDS observation convinced this process. And the DLVO theory explained this heteroaggregation process under various EPS conditions, where the energy barrier decreased with gradual EPS extraction. In addition, the order for 96 h half growth inhibition concentration (IC₅₀) was Raw M9 > M9-SEPS > M9+BEPS > M9-BEPS. These results revealed that not all heteroaggregation between cell-NPs can lead to the NPs toxicity to cells. BEPS act more important role in buffering against the toxicity of NPs from ambient adverse factors, but SEPS increase the stability of NPs which could aggravate the adverse effects of NPs in the environment.

Characterization of extracellular polysaccharide/protein contents during the adsorption of Cd(II) by Synechocystis sp. PCC6803

Cyanobacteria have been proven to be cheaper and more effective for the removal of metallic elements in aqueous solutions. In this study, the living cyanobacteria Synechocystis sp. PCC6803 was used to adsorb Cd(II) and its extracellular polymeric substances (EPS) were investigated in the adsorption process. The initial stage of adsorption of Cd(II) was a rapid process, and then increase slowly accompanied with the increases of biomass. The final adsorption percentage could achieve 86% when the Cd(II) concentration was 0.5 mg/L. It proved that Synechocystis sp. PCC6803 has a good adsorption capacity for heavy metal ions. EPS was extracted to investigate the secretion of which was dynamic and the maximum extracellular polysaccharides and proteins were 134.2 and 100.9 mg/g, respectively. Furthermore, the real-time PCR (RT-PCR) results of genes (slr0977 and exoD) involved in EPS synthesis and secretion indicated that the EPS production was firstly increased and then decreased slightly. Transmission electron microscope (TEM) observation revealed that heavy metal ions were absorbed into EPS layer. Fourier transform infrared spectrum (FT-IR) analysis showed that EPS was rich in functional groups which could combine with heavy metal ions, such as -OH and -NH groups. All the results obtained show that the secretion of EPS by cyanobacteria was one of the ways to resist heavy metal stress. And it shows a trend of rising first and then decreasing, the change regulation of which was consistent with adsorptive behavior.