Thermodynamics of binding interactions between extracellular polymeric substances and heavy metals by isothermal titration microcalorimetry

Deciphering the mechanisms for preferential tolerance of Escherichia coli BL21 to Cd(II) over Cu(II) and Ni(II): A combined physiological, biochemical, and multiomics perspective

Environmental pollution severely affects ecological functions/health, and nondegradable pollutants such as heavy metals (HMs) cause significant damage to living organisms. Escherichia coli is one of the most studied life forms, and its response to oxidative stress is driven by a complex ensemble of mechanisms driven by transcriptomic-level adjustments. However, the magnitude of the physiological, metabolic, and biochemical alterations and their relationships with transcriptomic changes remain unclear. Studying the growth of E. coli in Cd-, Cu-, and Ni-polluted media at pH 5.0, we observed that (i) downregulation of the alkyl hydroperoxide complex, glutathione reductase, and glutathione S-transferase by Cd inhibited H2O2 degradation, and the accumulated H2O2 was respectively 2.7, 1.7, and 2.4 times greater than that in the control, Cu, and Ni treatments; (ii) Zn-associated resistance protein (ZraP) was the major scavenger of Cd, with a 140.7-fold increase in its expression; (iii) the P-type Cu+ transporter (CopA), multicopper oxidase (CueO), and heteromultimeric transport system (CusCBAF) controlled the excretion and detoxification of Cu; (iv) the Cd2+/Zn2+/Pb2+-exporting P-type ATPase (ZntA) and transcriptional activator ZntR were the major transporters of Ni; (v) Cd upregulated biofilm formation and synthesis of secondary metabolites more than Cu and Ni, which resulted in increased adsorption and improved tolerance; and (vi) the activity of superoxide dismutase in Cu-spiked cells was 153.2 %, 141.7 %, and 172.7 % higher and corresponded to 85.7 %, 524.5 %, and 491.5 % lower O2●⁻ in the control, Cd-, and Ni-spiked cells, respectively. This study reveals E. coli's preferential tolerance mechanisms to Cd rather than Cu and Ni and demonstrates mechanisms for its survival in highly polluted environments.

Inhibition of zinc ions in sulfur-driven autotrophic denitrification process: What is the behavior of extracellular polymeric substances?

Sulfur-driven autotrophic denitrification (SAD) process is a cost-effective and sustainable method for nitrogen removal from wastewater. However, a higher concentration of zinc ions (Zn(II)) flowing into wastewater treatment plants poses a potential threat to the SAD process. This study examined that a half maximal inhibitory concentration (IC50) of Zn(II) was 7 mg·L-1 in the SAD process. Additionally, the addition of 20 mg·L-1 Zn(II) resulted in a severe accumulation of nitrite to 150.20 ± 6.00 mg·L-1 when the initial concentration of nitrate was 500 mg·L-1. Moreover, the activities of nitrate reductase, nitrite reductase, dehydrogenase and electron transport system were significantly inhibited under Zn(II) stress. The addition of Zn(II) inhibited EPS secretion and worsened electrochemical properties. The result was attributed to the spontaneous binding between EPS and Zn(II), with a ΔG of -17.50 KJ·mol-1 and a binding constant of 1.77 × 104 M-1, respectively. Meanwhile, the protein, fulvic acid, and humic-like substances occurred static quenching after Zn(II) addition, with -OH and -C=O groups providing binding sites. The binding sequence was fulvic acid→protein→humic acid and -OH → -C=O. Zn(II) also reduced the content of α-helix, which was unfavorable for electron transfer. Additionally, the Zn(II) loosened protein structure, resulting in a 50 % decrease in α-helix/(β-sheet+random coil). This study reveals the effect of Zn(II) on the SAD process and enhances our understanding of EPS behavior under metal ions stress.

Simultaneous extraction of five heavy metal ions from root vegetables via dual-frequency ultrasound-assisted enzymatic digestion

The dual-frequency ultrasound-assisted enzymatic digestion (DUED) technique was developed for synchronous green extraction of five heavy metal ions in root vegetables. The combination of α-amylase, cellulase, and papain showed significant advantageous in extracting heavy metal ions. Under optimized dual-frequency ultrasonic conditions, the extraction rates of Cr, As, Cd, Pb, and Hg in carrots reached 99.04%, 105.88%, 104.65%, 104.10%, and 103.13% respectively. And the extraction process is highly efficient, completing in just 15 min. Compared to conventional microwave-assisted acid hydrolysis method, this technique eliminates the need for high-temperature concentrated acid, enhancing its environmental sustainability while maintaining mild reaction conditions, making it ideal for biosensors application. Additionally, simultaneous extraction and detection of four heavy metals in lotus roots were successfully achieved by using DUED and a fluorescent paper-based microfluidic chip. The obtained results are consistent with those obtained using conventional methods.

Applications of Bioactive Strontium Compounds in Dentistry

Divalent cations have captured the interest of researchers in biomedical and dental fields due to their beneficial effects on bone formation. These metallic elements are similar to trace elements found in human bone. Strontium is a divalent cation commonly found in various biomaterials. Since strontium has a radius similar to calcium, it has been used to replace calcium in many calcium-containing biomaterials. Strontium has the ability to inhibit bone resorption and increase bone deposition, making it useful in the treatment of osteoporosis. Strontium has also been used as a radiopacifier in dentistry and has been incorporated into a variety of dental materials to improve their radiopacity. Furthermore, strontium has been shown to improve the antimicrobial and mechanical properties of dental materials, promote enamel remineralization, alleviate dentin hypersensitivity, and enhance dentin regeneration. The objective of this review is to provide a comprehensive review of the applications of strontium in dentistry.

Unveiling the biointerfaces characteristics and removal pathways of Cr(Ⅵ) in Bacillus cereus FNXJ1-2-3 for the Cr(Ⅵ)-to-Cr(0) conversion

Although less toxic than hexavalent chromium, Cr (Ⅲ) species still pose a threat to human health. The Cr (Ⅵ) should be converted to Cr (0) instead of Cr (Ⅲ), which is still involved in biological detoxification filed. Herein, for the first time, it was found that Cr(Ⅵ) can be reduced into Cr(0) by Bacillus cereus FNXJ1-2-3, a way to completely harmless treatment of Cr(Ⅵ). The bacterial strain exhibited excellent performance in the reduction, sorption, and accumulation of Cr(Ⅵ) and Cr (Ⅲ). XPS etching characterization inferred that the transformation of Cr(Ⅵ) into Cr(0) followed a reduction pathway of Cr(Ⅵ)→Cr (Ⅲ)→metallic Cr(0), in which at least two secretory chromium reductases (ECrⅥ→Ⅲ and ECrⅢ→0) worked. Under the optimum condition, the yield ratio of Cr(0)/Cr (Ⅲ) reached 33.90%. In addition, the interfacial interactions, ion channels, chromium reductases, and external electron donors also contributed to the Cr(Ⅵ)/Cr(0) transformation. Findings of this study indicate that Bacillus cereus FNXJ1-2-3 is a promising bioremediation agent for Cr(Ⅵ) pollution control.

Magnetite alleviating calcification of anaerobic granular sludge (AnGS): Electron transfer enhancement and ion competition

Calcification accompanied by deactivation of anaerobic granular sludge (AnGS) is a continuing challenge for high calcium wastewater treatment. The interaction between Ca2+ and extracellular polymeric substances (EPS) is a precondition for this problem. In this study, magnetite for activity recovery and calcification alleviation simultaneously of AnGS under high calcium stress was investigated. The results showed that, in the presence of magnetite, the relative biogas production increased by 13.2 % with the higher activities of key enzymes involved in methanogenesis. Methanosarcina turned into the dominant methanogens, and syntrophic bacteria such as Chloroflexi, Synergistota were enriched, which indicated the enhancement of electron transfer by magnetite, supported by an 18 % increase of the electron transfer system (ETS) activity. Further characterizations of AnGS suggested that the granule calcification was alleviated with a final decrease of 13-40 % calcium content of AnGS with particle size of 1-2.5 mm. Besides, calcium was partially substituted by iron in the EPS, and the secretion of EPS especially proteins decreased. Batch tests demonstrated the competition between Fe2+ dissolved from magnetite and Ca2+, which interfered the interaction between Ca2+ and EPS, so the granule calcification was prevented. Therefore, magnetite played a pluripotent role in the alleviation of granule calcification and deactivation in situ via (1) enhancing electron transfer, and (2) blocking the complex between Ca2+ and EPS. This study provides a novel insight into the application of conductive metal materials in biological wastewater treatment systems suffering from high calcium attack.

Algal Extracellular Organic Matter Induced Photochemical Oxidation of Mn(II) to Solid Mn Oxide: Role of Mn(III)-EOM Complex and Its Ability to Remove 17α-Ethinylestradiol

Photosensitizer-mediated abiotic oxidation of Mn(II) can yield soluble reactive Mn(III) and solid Mn oxides. In eutrophic water systems, the ubiquitous algal extracellular organic matter (EOM) is a potential photosensitizer and may have a substantial impact on the oxidation of Mn(II). Herein, we focused on investigating the photochemical oxidation process from Mn(II) to solid Mn oxide driven by EOM. The results of irradiation experiments demonstrated that the generation of Mn(III) intermediate was crucial for the successful photo oxidization of Mn(II) to solid Mn oxide mediated by EOM. EOM can serve as both a photosensitizer and a ligand, facilitating the formation of the Mn(III)-EOM complex. The complex exhibited excellent efficiency in removing 17α-ethinylestradiol. Furthermore, the complex underwent decomposition as a result of reactions with reactive intermediates, forming a solid Mn oxide. The presence of nitrate can enhance the photochemical oxidation process, facilitating the conversion of Mn(II) to Mn(III) and then to solid Mn oxide. This study deepens our grasp of Mn(II) geochemical processes in eutrophic water and its impact on organic micropollutant fate.

Spectra metrology for interaction of heavy metals with extracellular polymeric substances (EPS) of Pseudomonas aeruginosa OMCS-1 reveals static quenching and complexation dynamics of EPS with heavy metals

The adsorption behavior and interaction mechanisms of extracellular polymeric substances (EPS) of Pseudomonas aeruginosa OMCS-1 towards chromium (Cr), lead (Pb), and cadmium (Cd) were investigated. EPS-covered (EPS-C) cells exhibited significantly higher (p < 0.0001; two-way ANOVA) removal of Cr (85.58 ± 0.39%), Pb (81.98 ± 1.02%), and Cd (73.88 ± 1%) than EPS-removed (EPS-R) cells. Interactions between EPS-heavy metals were spontaneous (ΔG<0). EPS-Cr(VI) and EPS-Pb(II) binding were exothermic (ΔH<0), while EPS-Cd(II) binding was endothermic (ΔH>0) process. EPS bonded to Pb(II) via inner-sphere complexation by displacement of surrounding water molecules, while EPS-Cr(VI) and EPS-Cd(II) binding occurred through outer-sphere complexation via electrostatic interactions. Increased zeta potential of Cr (29.75%), Pb (41.46%), and Cd (46.83%) treated EPS and unchanged crystallinity (CIXRD=0.13), inferred EPS-metal binding via both electrostatic interactions and complexation mechanism. EPS-metal interaction was predominantly promoted through hydroxyl, amide, carboxyl, and phosphate groups. Metal adsorption deviated EPS protein secondary structures. Strong static quenching mechanism between tryptophan protein-like substances in EPS and heavy metals was evidenced. EPS sequestered heavy metals via complexation with C-O, C-OH, CO/O-C-O, and NH/NH2 groups and ion exchange with -COOH group. This study unveils the fate of Cr, Pb, and Cd on EPS surface and provides insight into the interactions among EPS and metal ions for metal sequestration.

Application of biological soil crusts for efficient cadmium removal from acidic mine wastewater

Utilizing an acid-resistant biological soil crust (BSC) species that we discovered, we developed a device capable of efficiently removing cadmium (Cd) from mine wastewater with varying levels of acidity. Our research has demonstrated that this particular BSC species adapts to acidic environments by regulating the balance of fatty acids and acid-resistant enzymes. At a Cd concentration of 5 mg/L, the BSC grew well. When the initial Cd concentration was 2 mg/L, and the flow rate was set at 1 mL/min (at pH levels of 3, 4, and 5), BSC had a high removal rate of Cd, and the removal rate increased with the increase of pH (from 90% to 97%). Chemisorption is the primary removal mechanism in the initial stage, where the functional groups and minerals on the surface of the BSC play a significant role. In addition, BSC also adapts to Cd stress by changing bacterial community structure. It was discovered through infrared spectroscopy and two-dimensional correlation analysis that hydrophilic groups, specifically phosphate and carboxyl groups, exhibited the highest reactivity during the Cd binding process. Protein secondary structure analysis confirmed that as the pH increased, the adsorption capacity of the BSC increased; making biofilm formation easier. This study presents a novel approach for the treatment of acidic wastewater.

Transport and transformations of cadmium in water-biofilm-sediment phases as affected by hydrodynamic conditions

Hydrodynamic conditions play a crucial role in governing the fate, transport, and risks of metal elements. However, the contribution of hydrodynamic conditions to the fate and transport of heavy metals among water, sediment, and biofilm phases is poorly understood. In our study, we conducted experiments in controlled hydrodynamic conditions using a total of 6 two-phase and 9 three-phase mesocosms consisting of water, biofilm, and sediment. We also measured Cd (cadmium) specification in different phases to assess how hydrodynamic forces control Cd bioavailability. We found that turbulent flow destroyed the surface morphology of the biofilm and significantly decreased the content of extracellular polymeric substances (p < 0.05). This led to a decrease in the biofilm's adsorption capacity for Cd, with the maximum adsorption capacity (0.124 mg/g) being one-tenth of that under static conditions (1.256 mg/g). The Cd chemical forms in the biofilm and sediment were significantly different, with the highest amount of Cd in the biofilm being acid-exchangeable, accounting for up to 95.1% of the total Cd content. Cd was more easily released in the biofilm due to its weak binding state, while Cd in the sediment existed in more stable chemical forms. Hydrodynamic conditions altered the migration behavior and distribution characteristics of Cd in the system by changing the adsorption capacity of the biofilm and sediment for Cd. Cd mobility increased in laminar flow but decreased in turbulent flow. These results enhance our understanding of the underlying mechanisms that control the mobility and bioavailability of metals in aquatic environments with varying hydrodynamic conditions.

Lead remediation by geological fluorapatite combined with Penicillium Oxalicum and Red yeast

Phosphate solubilizing fungi Penicillium oxalicum (POX) and Red yeast Rhodotorula mucilaginosa (Rho) have been applied in Pb remediation with the combination of fluorapatite (FAp), respectively. The secretion of oxalic acid by POX and the production of extracellular polymers (EPS) by Rho dominate the Pb remediation. In this study, the potential of Pb remediation by the fungal combined system (POX and Rho) with FAp was investigated. After six days of incubation, the combination of POX and Rho showed the highest Pb remove ratio (99.7%) and the lowest TCLP-Pb concentration (2.9 mg/L). The EPS combined with POX also enhanced Pb remediation, which has a 99.3% Pb removal ratio and 5.5 mg/L TCLP-Pb concentration. Meanwhile, Rho and EPS can also stimulate POX to secrete more oxalic acid, which reached 1510.1 and 1450.6 mg/L in six days, respectively. The secreted oxalic acid can promote FAp dissolution and the formation of lead oxalate and pyromorphite. Meanwhile, the EPS produced by Rho can combine with Pb to form EPS-Pb. In the combined system of POX + Rho and POX + EPS, all of the lead oxalate, pyromorphite, and EPS-Pb were observed. Our findings suggest that the combined application of POX and Rho with FAp is an effective approach for enhancing Pb remediation.

Insights into the role of extracellular polymeric substances (EPS) in the spread of antibiotic resistance genes

Antibiotic resistance genes (ARG) are prevalent in aquatic environments. Discharge from wastewater treatment plants is an important point source of ARG release into the environment. It has been reported that biological treatment processes may enhance rather than remove ARG because of their presence in sludge. Attenuation of ARG in biotechnological processes has been studied in depth, showing that many microorganisms can secrete complex extracellular polymeric substances (EPS). These EPS can serve as multifunctional elements of microbial communities, involving aspects, such as protection, structure, recognition, adhesion, and physiology. These aspects can influence the interaction between microbial cells and extracellular ARG, as well as the uptake of extracellular ARG by microbial cells, thus changing the transformative capability of extracellular ARG. However, it remains unclear whether EPS can affect horizontal ARG transfer, which is one of the main processes of ARG dissemination. In light of this knowledge gap, this review provides insight into the role of EPS in the transmission of ARGs; furthermore, the mechanism of ARG spread is analyzed, and the molecular compositions and functional properties of EPS are summarized; also, how EPS influence ARG mitigation is addressed, and factors impacting how EPS facilitate ARG during wastewater treatment are summarized. This review provides comprehensive insights into the role of EPS in controlling the transport and fate of ARG during biodegradation processes at the mechanistic level.

Electrochemical surface plasmon resonance approach to probe redox interactions between microbial extracellular polymeric substances and p-nitrophenol

Microbial extracellular polymeric substances with redox functional groups play a crucial role in the bio-conversion of pollutants, which can affect their reactivity toward diverse pollutants. However, the redox interactions between microbial EPS and pollutants have not addressed in depth due to the absence of essential analytical methodologies. In this study, we have developed an electrochemical-surface plasmon resonance (EC-SPR) system to investigate the interactions between EPS and p-nitrophenol (PNP) by simultaneously monitoring the electrochemical reaction and the binding kinetics. Moreover, in vitro PNP degradation experiments were performed in the presence of EPS across varying redox states to provide further verification of PNP reduction by EPS. The results indicated that direct electrochemical treatment successfully converted raw EPS (EPSraw) into reductive EPS (EPSred) and oxidized EPS (EPSox), respectively. The EC-SPR system served as a powerful tool for probing redox interactions between EPS at distinct redox states and PNP. The binding affinity of EPS to PNP was related to the redox states of EPS, following the order of EPSred > EPSraw > EPSox. EPS exhibited the capability to reduce PNP to p-aminophenol by donating electrons, and the reductive process highly depended on the redox states of EPS, primarily determined by their electron donating capacity. Importantly, direct electrochemical reduction treatment of EPS leads to a substantial improvement in the PNP removal efficiency from 33.8% (EPSraw) to 56.9% (EPSred). This work contributes to a comprehensive understanding of the critical role of EPS redox property in the conversion of refractory pollutants in aquatic environments.

Algal organic matter and dissolved Mn cooperatively accelerate 17α-ethinylestradiol photodegradation: Role of photogenerated reactive Mn(III)

Algal extracellular organic matter (EOM), a major fraction of the dissolved organic matter found in eutrophic plateau lakes, can act as a photosensitizer to drive the abiotic oxidation of Mn(II). This process has the potential to generate reactive Mn(III) and influence the fate of organic pollutants. In this study, the photodegradation of 17α-ethinylestradiol (EE2) in the presence of Mn(II) and EOM was investigated with emphasis on the photogeneration mechanism of Mn(III). The results indicated that Mn(II) can accelerate EE2 photodegradation in EOM solution owing to the photogeneration of reactive Mn(III), and the enhancement was greater at higher Mn(II) concentrations. The generation of reactive Mn(III) was mainly attributable to the action of superoxide radical generated by photosensitization of EOM. In addition, the photodegradation of EE2 was slower at higher pH, possibly because of the deactivation of Mn(III) under alkaline conditions. Single-electron transfer was an indispensable process in the photodegradation. The differences in fluorophore content, pH, and NO₃^- concentrations are all important determinants for EE2 photodegradation in natural waters. The information obtained in this research would contribute to the understanding of reactions between Mn(II) and EOM, and provide new insights into the behaviors of reactive Mn(III) in eutrophic water irradiated by sunlight.

Impacts of metal stress on extracellular microbial products, and potential for selective metal recovery

Harnessing microbial capabilities for metal recovery from secondary waste sources is an eco-friendly and sustainable approach for the management of metal-containing wastes. Soluble microbial products (SMP) and extracellular polymeric substances (EPS) are the two main groups of extracellular compounds produced by microorganisms in response to metal stress that are of great importance for remediation and recovery of metals. These include various high-, and low, molecular weight components, which serve various functional and structural roles. These compounds often contain functional groups with metal binding potential that can attenuate metal stress by sequestering metal ions, making them less bioavailable. Microorganisms can regulate the content and composition of EPS and SMP in response to metal stress in order to increase the compounds specificity and capacity for metal binding. Thus, EPS and SMP represent ideal candidates for developing technologies for selective metal recovery from complex wastes. To discover highly metal-sorptive compounds with specific metal binding affinity for metal recovery applications, it is necessary to investigate the metal binding affinity of these compounds, especially under metal stressed conditions. In this review we critically reviewed microbial EPS and SMP production as a response to metal stress with a particular emphasis on the metal binding properties of these compounds and their role in altering metal bioavailability. Furthermore, for the first time, we compiled the available data on potential application of these compounds for selective metal recovery from waste streams.

Bacterial coculture enhanced Cd sorption and As bioreduction in co-contaminated systems

The bacterial interactions that regulate Cd sorption and As bioreduction in co-contaminated systems are poorly understood. We isolated two bacterial strains, i.e., Pseudomonas aeruginosa and Bacillus licheniformis from a Cd and As co-contaminated soil and compared the effects of monoculture and coculture on microbial Cd sorption and As bioreduction efficiency in the media with different Cd (0, 0.5, 5, 10, 50, 100 mg/L) and As(Ⅴ) (0, 90 mg/L) concentrations. Compared with monoculture, the bacterial coculture increased the Cd sorption efficiency by up to 32% and the As bioreduction (As(Ⅴ) to As(Ⅲ)) efficiency by up to 28%, associated with the increased abundance of As reduction gene arsB. Based on SEM-TEM and metabolomics, the enhanced efficiency was attributed to bacterial interactions, supported by the differential secretion of extracellular polymeric substances. Notably, the differential lipids and lipid-like molecules, and organoheterocyclic compounds resulted from bacterial interactions compared to monoculture exhibited the highest Cd sorption and As bioreduction. The increased efficiencies by bacterial coculture were verified by soil incubation experiments. These results provide insight on applying specific bacterial coculture and their metabolites to enhance Cd sorption and As bioreduction in effective and sustainable remediation of co-contaminated environments.

Functionalized maghemite nanoparticles for enhanced adsorption of uranium from simulated wastewater and magnetic harvesting

Maghemite (γ-Fe₂O₃) nanoparticles (MNPs) were functionalized with 3-aminopropyltriethoxysilane (APTES) to give APTES@Fe₂O₃ (AMNP) which was then reacted with diethylenetriamine-pentaacetic acid (DTPA) to give a nanohybrid DTPA-APTES@Fe₂O₃ (DAMNP). Nano-isothermal titration calorimetry shows that DTPA complexation with uranyl ions in water is exothermic and has a stoichiometry of two DTPA to three uranyl ions. Density functional theory calculations indicate the possibility of several complexes between DTPA and UO₂²⁺ with different stoichiometries. Interactions between uranyl ions and DAMNP functional groups are revealed by X-photoelectron and Fourier transform infrared spectroscopies. Spherical aberration-corrected Scanning Transmission Electron Microscopy visualizes uranium on the particle surface. Adsorbent performance metrics were evaluated by batch adsorption studies under different conditions of pH, initial uranium concentration and contact time, and the results expressed in terms of equilibrium adsorption capacities (q_e) and partition coefficients (PC). By either criterion, performance increases from MNP to AMNP to DAMNP, with the maximum uptake at pH 5.5 in all cases: MNP, q_e = 63 mg g^-1, PC = 127 mg g^-1 mM^-1; AMNP, q_e = 165 mg g^-1, PC = 584 mg g^-1 mM^-1; DAMNP, q_e = 249 mg g^-1, PC = 2318 mg g^-1 mM^-1 (at 25 °C; initial U concentration 0.63 mM; 5 mg adsorbent in 10 mL of solution; contact time, 3 h). The pH maximum is related to the predominance of mono- and di-cationic uranium species. Uptake by DAMNPs follows a pseudo-first-order or pseudo-second-order kinetic model and fits a variety of adsorption models. The maximum adsorption capacity for DAMNPs is higher than for other functionalized magnetic nanohybrids. This adsorbent can be regenerated and recycled for at least 10 cycles with less than 10% loss in activity, and shows high selectivity. These findings suggest that DAMNP could be a promising adsorbent for the recovery of uranium from nuclear wastewaters.

Alginate-like polymers from full-scale aerobic granular sludge: content, recovery, characterization, and application for cadmium adsorption

Aerobic granular sludge (AGS) is a proven resource for the recovery of biopolymers like alginate-like polymers (ALP). This is the first report on the dynamics of ALP produced by AGS (ALP-AGS) in a full-scale wastewater treatment plant (WWTP), optimization of ALP recovery from AGS, and adsorption of cadmium (Cd2+) by ALP. Recovery of ALP was highest when using 120 mL of 0.2 M Na2CO3 at 70 °C for 45 min. Seasonal (1.5 years, over 3100 cycles) and intra-cycle changes in ALP-AGS in the WWTP were monitored. The ALP content in AGS increased in the transition period between winter and spring, reaching over 150 mg/g MLSS. In the batch reactor cycle, the ALP-AGS level peaked 2 h after the start of aeration (mean peak level: 120 mg/g MLSS), then decreased about two-fold by the end of the cycle. The ALP-AGS had a small surface area and a lamellar structure with crystalline outgrowths. The optimal conditions of Cd2+ adsorption with ALP were a dosage of 7.9 g d.m./L, a pH of 4-8, and an equilibrium time of 60 min. Carboxyl and hydroxyl groups were the key functional groups involved in Cd2+ adsorption. According to the Sips model, the maximum Cd2+ adsorption capacity of ALP-AGS was 29.5 mg/g d.m., which is similar to that of commercial alginate. AGS is a richer source of ALP than activated sludge, which ensures the cost-effectiveness of ALP recovery and increases the sustainability of wastewater treatment. Information on the chemical properties and yields of ALP from full-scale WWTPs is important for downstream applications with the recovered ALP.

Interactions between tannins allelochemicals and extracellular polymeric substance (EPS) of Microcystis aeruginosa

The protective mechanism of extracellular polymeric substance (EPS) secreted by a harmful cyanobacteria against tannins allelochemicals was explored in this study. The binding properties of soluble EPS (SEPS) and bound EPS (BEPS) of Microcystis aeruginosa to tannic acid (TA) were investigated via fluorescence spectroscopy. The results suggested that TA interacted with the proteins in SEPS and BEPS mainly with binding constants of 5.26 and 7.93 L/mol, respectively; TA interacted with the humic acids in SEPS and BEPS mainly with binding constants of 5.12 and 5.24 L/mol, respectively. Thermodynamic experiments confirmed that the binding was mainly controlled by the hydrophobic force. Combined with Fourier transform infrared spectroscopy, it was found that the amine, carbonyl, carboxyl, and hydroxyl groups in EPS were the main functional groups contributing to the interaction of TA with EPS. The existence of EPS reduced the toxicity of TA to algal cells, with the 96 h inhibition rate of 40 mg L^-1 TA on algal cells decreasing by 48.95%. The results of this study may improve our understanding of the protective mechanism of cyanobacteria against tannins allelochemicals.

Exploring the impact of intensity and duration of Cu (II) depression on aniline-degrading biosystem: Performance, sludge activity and microbial diversity

To evaluate the ecological risk of aniline wastewater biodegradation, the aniline wastewater (200 mg/L) was treated in this work under the stress of Cu (II) at 3, 6 and 10 mg/L, respectively. The slight fluctuation of aniline-degrading performance and the significant inhibition of nitrogen removal was caused by the Cu (II) stress at below 6 mg/L. Meanwhile, the tolerance of nitrifying performance to Cu (II) was higher than denitrifying. The collapse of biosystem was caused by the Cu (II) stress at 10 mg/L and the decontamination function was disabled within 8 days. The activity and stability of sludge declined under the increase of Cu (II) content. Microbial diversity results demonstrated that the genera with heavy-metal tolerance represented by Zoogloea and Azospira significantly dominated under the continuously Cu (II) stress. Whereas, the biosystem with these dominant genera did not achieve the comparable aniline and nitrogen removal performance as the control group.

Longitudinal physiological and transcriptomic analyses reveal the short term and long term response of Synechocystis sp. PCC6803 to cadmium stress

Due to the bioaccumulation and non-biodegradability of cadmium, Cd can pose a serious threat to ecosystem even at low concentration. Microalgae is widely distributed photosynthetic organisms in nature, which is a promising heavy metal remover and an effective industrial sewage cleaner. However, there are few detailed reports on the short-term and long-term molecular mechanisms of microalgae under Cd stress. In this study, the adsorption behavior (growth curve, Cd removal efficiency, scanning electron microscope, Fourier transform infrared spectroscopy, and dynamic change of extracellular polymeric substances), cytotoxicity (photosynthetic pigment, MDA, GSH, H₂O₂, O₂^-) and stress response mechanism of microalgae were discussed under EC50. RNA-seq detected 1413 DEGs in 4 treatment groups. These genes were related to ribosome, nitrogen metabolism, sulfur transporter, and photosynthesis, and which been proved to be Cd-responsive DEGs. WGCNA (weighted gene co-expression network analysis) revealed two main gene expression patterns, short-term stress (381 genes) and long-term stress (364 genes). The enrichment analysis of DEGs showed that the expression of genes involved in N metabolism, sulfur transporter, and aminoacyl-tRNA biosynthesis were significantly up-regulated. This provided raw material for the synthesis of the important component (cysteine) of metal chelate protein, resistant metalloprotein and transporter (ABC transporter) in the initial stage, which was also the short-term response mechanism. Cd adsorption of the first 15 min was primary dependent on membrane transporter and beforehand accumulated EPS. Simultaneously, the up-regulated glutathione S-transferase (GSTs) family proteins played a role in the initial resistance to exogenous Cd. The damaged photosynthetic system was repaired at the later stage, the expressions of glycolysis and gluconeogenesis were up-regulated, to meet the energy and substances of physiological metabolic activities. The study is the first to provide detailed short-term and long-term genomic information on microalgae responding to Cd stress. Meanwhile, the key genes in this study can be used as potential targets for algae-mediated genetic engineering.

Spectroscopic Investigation on the Interaction of Direct Yellow-27 with Protein (BSA)

Direct yellow 27 (DY-27) interaction with bovine serum albumin (BSA) was investigated using multi-spectroscopic techniques to understand the toxicity mechanism. Fluorescence quenching of BSA by DY-27 was observed as a result of the formation of a BSA-DY27 complex with a binding constant of 1.19 × 10⁵M^-1and followed a static quenching mechanism with a quenching constant K_svof 7.25 × 10⁴M^-1. The far UV circular dichroism spectra revealed the conformational changes in the secondary structure of BSA in the presence of DY-27. The calculated average lifetime of BSA is 6.04 ns and is nearly constant (5.99 ns) in the presence of dye and supports the proposed quenching mechanism. The change in free energy (ΔG) was calculated to be -28.96 kJ mol^-1and confirmed the spontaneity of the binding process. Further, docking studies have been conducted to gain more insights into the interactions between DY-27 and serum albumin.

Surface biomineralization of uranium onto Shewanella putrefaciens with or without extracellular polymeric substances

The influence of extracellular polymeric substances (EPS) on the interaction between uranium [U(VI)] and Shewanella putrefaciens (S. putrefaciens), especially the U(VI) biomineralization process occurring on whole cells and cell components of S. putrefaciens was investigated in this study. The removal efficiency of U(VI) by S. putrefaciens was decreased by 22% after extraction of EPS. Proteins were identified as the main components of EPS by EEM analysis and were determined to play a major role in the biosorption of uranium. SEM-EDS results showed that U(VI) was distributed around the whole cell as 500-nanometer schistose structures, which consisted primarily of U and P. However, similar uranium lamellar crystal were wrapped only on the surface of EPS-free S. putrefaciens cells. FTIR and XPS analysis indicated that phosphorus- and nitrogen-containing groups played important roles in complexing U (VI). XRD and U L_III-edge EXAFS analyses demonstrated that the schistose structure consisted of hydrogen uranyl phosphate [H₂(UO₂)₂(PO₄)₂•8H₂O]. Our study provides new insight into the mechanisms of induced uranium crystallization by EPS and cell wall membranes of living bacterial cells under aerobic conditions.

Insight into halotolerance of a robust heterotrophic nitrifying and aerobic denitrifying bacterium Halomonas salifodinae

Studies toward biotreating hypersaline wastewater containing different salts and halotolerant mechanism of robust strains are important but still rare. Here an isolated bacterium Halomonas salifodinae can perform simultaneous nitrification and denitrification (SND) at 15% salinity, showing high nitrogen removal efficiencies of over 98% via response surface methodology optimization. Besides NaCl, this robust strain had high resistance to other salts (KCl, Na₂SO₄, and K₂SO₄) and can efficiently remove nitrogen in saline wastewater containing heavy metals such as Fe(II), Mn(II), Zn(II), Cr(VI), Ni(II), and Cu(II). After repeated-batch culturing at different salinities, the treated strains with different halotolerant capabilities were used as single strain model to study halotolerant mechanism via metabolic analysis. The halotolerant bacterium can convert D-proline and glutamic acid to glutamine as well as lactulose to trehalose. The accumulated intracellular compatible solutes can resist high osmotic pressure and bound water molecule in hypersaline wastewater to accomplish high-efficiency SND processes.

Characterization of Neodymium Speciation in the Presence of Fulvic Acid by Ion Exchange Technique and Single Particle ICP-MS

It has been well known that the free ion concentration of metals plays a vital role in metal bioavailability. However, measurement of this fraction is still not easy over years of development. Nowadays, rare earth elements (REEs) are drawing more attentions as an emerging contaminant due to their wide applications in our daily life. To analyze the free ion concentration of neodymium (Nd), we adopted ion-exchange technique (IET) to investigate the changes on Nd free ion concentration in the presence of fulvic acid (FA). With the dynamic mode of IET analysis, the concentrations of Nd free ion were in the range of 0.85-36.8 × 10^-8 M at the total Nd concentration of 5 × 10^-7 M when FA varied from 0.4 to 10 M. However, these concentrations were 3-58 times higher than the one calculated by WHAM 7.0, which may be due to the particulate Nd spontaneously formed in solution. With single particle ICP-MS analysis, we found 0.25%-2.36% of Nd was in the form of colloids when the total Nd concentrations varied from 8.5 × 10^-9 to 4.7 × 10^-7 M, with the average particle sizes in the range of 26.5-39.2 nm. The presence of FA significantly decreased the number of Nd colloids, but increased the average particle size. Under the TEM, we found that Nd colloids were amorphous, with the size less than 200 nm. The present study provided a relatively new perspective on REE speciation in water. The natural organic matters not only affect the free ion concentration of Nd, but also influenced the size and numbers of Nd colloids in solution.

Remediation of Lead-Contaminated Water by Red Yeast and Different Types of Phosphate

Rhodotorulamucilaginosa (Rho) can secrete large amounts of extracellular polymeric substances (EPS) to resist lead (Pb) toxicity. Phosphate is an effective material for the remediation of Pb. This study explored the Pb remediation by the combination of Rho and different types of phosphate in water. To do so, four phosphates, namely, ferric phosphate (FePO₄, Fe-P), aluminum phosphate (AlPO₄, Al-P), calcium phosphate [Ca₃(PO₄)₂, Ca-P], and phosphogypsum (PG) were employed along with Rho. Compared with Rho application, the addition of phosphate significantly promoted the secretion of EPS by Rho (21–25 vs 16 mg). The formed EPS-Pb contributes to the Pb immobilization in the combination of Rho and phosphate. After 6 days of incubation, Rho + phosphate treatments immobilized over 98% of Pb cations, which is significantly higher than Rho treatment (94%). Of all Rho + phosphate treatments, Ca-P and PG-amended Rho had higher secretion of EPS, resulting in higher Pb removal. Nevertheless, PG had the highest efficiency for Pb removal compared with other phosphates, which reached 99.9% after 6 days of incubation. Likewise, new Pb minerals, such as pyromorphite and lead sulfate, only appeared in Rho + PG treatment. Altogether, this study concludes on the combined application of Rho and phosphate as an efficient approach to promote Pb remediation, particularly using PG waste.

Insights into the role of extracellular DNA in heavy metal adsorption

Extracellular polymeric substances (EPS) participate in heavy metal adsorption in the aquatic environments. Extracellular DNA (eDNA) is an essential component of EPS, but its involvement in metal binding remains ambiguous. Herein, the role of eDNA in Cd(II) and Ni(II) adsorption was described using a combination of semi-quantitative and qualitative approaches. EPS were extracted from Burkholderia sp. MBR-1 and eDNA accounted for 6.9% of the total mass of EPS. The eDNA in the extracted EPS was digested using the DNase II to prepare an eDNA-free EPS sample. Potentiometric titration unveiled that the number of total binding sites of the eDNA-free EPS was 19% lower than the untreated EPS. The Cd(II) and Ni(II) adsorption capacity of the eDNA-free EPS was lower than the untreated EPS at the pH range of 4-7. At pH 7, the results of batch adsorption experiments showed that removing eDNA from EPS resulted in declines of 12.6% and 15.7% in the adsorption capacities for Cd(II) and Ni(II), respectively. Furthermore, Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy unraveled that the phosphoryl groups and purines of eDNA are responsible for Cd(II) and Ni(II) complexation. The results demonstrated that eDNA plays an essential role in heavy metal adsorption.

Inhibition of phosphate sorptions on four soil colloids by two bacteria

Ion sorption on soil and sediment has been reported to be potentially affected by bacteria which may interact both physically and chemically with solid surfaces. However, whether and how bacteria affect the sorption of inorganic phosphate (P) on soil colloids remains poorly known. Here, we comparably investigated the P sorption on four soil colloids (three highly weathered soils including two Oxisols and one Ultisol and one weakly weathered soil Alfisol) and their complexes with Bacillus subtilis and Pseudomonas fluorescens. Batch experiments showed a notable reduction in P sorption on the colloids of highly weathered soils by the two bacteria at varying P concentrations and pHs; whereas that on the colloids of Alfisol appeared to be unaffected by the bacteria. The inhibitory effect was confirmed by both greater decline in P sorption at higher bacteria dosages and the ability of the bacteria to desorb P pre-adsorbed on the colloids. Further evidence was given by isothermal titration calorimetric experiments which revealed an alteration in enthalpy change caused by the bacteria for P sorption on Oxisol but not for that on Alfisol. The B. subtilis was more efficient in suppressing P sorption than the P. fluorescens, indicating a dependence of the inhibition on bacterium type. After association with bacteria, zeta potentials of the soil colloids decreased considerably. The decrease positively correlated with the decline in P sorption, regardless of soil and bacterium types, demonstrating that the increment in negative charges of soil colloids by bacteria probably contributed to the inhibition. In addition, scanning electron microscopic observation and the Derjaguin-Landau-Verwey-Overbeek theory prediction suggested appreciable physical and chemical interactions between the bacteria and the highly weathered soil colloids, which might be another contributor to the inhibition. These findings expand our understandings on how bacteria mobilize legacy P in soils and sediments.

Enhanced Secretions of Algal Cell-Adhesion Molecules and Metal Ion-Binding Exoproteins Promote Self-Flocculation of Chlorella sp. Cultivated in Municipal Wastewater

The mechanism of self-flocculation remains unclear, partially impeding its efficiency enhancement and commercial application of microalgae-based municipal wastewater (MW) bioremediation technology. This study revealed the contributions of exoproteins [PN, proteins in extracellular polymeric substances (EPS)] to the separation of indigenous microalgae from treated MW. Compared to the low light intensity group, the high light intensity (HL) group produced Chlorella sp. with 4.3-fold higher self-flocculation efficiencies (SE). This was attributed to the enriched biological functions and positional rearrangement of increased PN within 2.9-fold higher EPS. Specifically, a total of 75 PN was over-expressed in the HL group among the 129 PN identified through label-free proteomics. The algal cell-adhesion molecules (Algal-CAMs) and metal-ion-binding PN were demonstrated as two dominant contributors promoting cell adhesion and bridging, through function prediction based on the contained domains. The modeled 3D structure showed that Algal-CAMs presented less hydrophilic α-helix abundance and were distributed in the outermost position of the EPS matrix, further facilitating microalgal separation. Moreover, the 10.1% lower hydrophily degree value, negative interfacial free energy (-19.5 mJ/m²), and 6.8-fold lower energy barrier between cells also supported the observed higher SE. This finding is expected to further fill the knowledge gap of the role of PN in microalgal self-flocculation and promote the development of biomass recovery from the microalgae-wastewater system.

Fluorescent Characteristics and Metal Binding Properties of Different Molecular Weight Fractions in Stratified Extracellular Polymeric Substances of Activated Sludge

The combination of heavy metals and extracellular polymeric substances (EPSs) affects the distribution of heavy metals in microbial aggregates, soil, and aquatic systems. This paper aimed to explore the binding mechanisms of EPSs of different molecular weights in activated sludge with heavy metals. We extracted the stratification components of activated sludge EPSs and divided the components into five fractions of different molecular weight ranges. In the three-dimensional fluorescence analysis of each fraction, the EPSs of activated sludge had two peaks, peak A (representing low-excitation tryptophan) and peak B (representing high-excitation tryptophan), and static quenching was the main reason for the fluorescence quenching between the compounds attributable to peak A in activated sludge EPSs and Pb2+ and Cu2+. Further exploration suggested that the EPSs of activated sludge interacted with Cd2+, Pb2+, Cu2+, and Zn2+ to form new substances. The quenching effect of the EPSs with the highest molecular weight (100 kDa–0.7 μm) was more significant, and the binding ability was more stable. This study implies that the application of EPSs from activated sludge is promising. While effectively binding heavy metals, it can also reduce the volume of the excess activated sludge.

Adaptation mechanism of aerobic denitrifier Enterobacter cloacae strain HNR to short-term ZnO nanoparticle stresses

The adaptation mechanism of a wild type (WT) and resistant type (Re) strain of the aerobic denitrifier Enterobacter cloacae strain HNR to short-term ZnO nanoparticle (NP) stresses was investigated. The results showed that Re maintained higher nitrite reductase (NIR) and nitrate reductase (NR) activities and showed lower increment of reactive oxygen species (ROS) than WT, under ZnO NP stresses. The affinity constant (K_A) of WT to Zn²⁺ was 5.06 times that of Re, indicating that Re was more repulsive to Zn²⁺ released by ZnO NPs. Transcriptomic analysis revealed that the up-regulation of the nitrogen metabolism of Re helped maintain NIR and NR activities, that the enhancement of purine metabolism lowered the intracellular ROS increment, and that the up-regulation of cationic antimicrobial peptide resistance contributed to the lower K_A of Re to Zn²⁺. These findings provided new insights into the adaptation mechanism of aerobic denitrifying bacteria to ZnO NPs.

Hydrogel composite of lanthanum and Halorubrum ejinoor sp. cell lysate as an adsorbing material

OBJECTIVES

Although halophilic archaea are rich in natural environments, their biotechnological applications are not as prevalent as those of other extremophiles, such as thermophiles and alkaliphiles. This study presents an simple method to prepare a hydrogel composite using crude cell lysate of a halophilic archaea, Halorubrum ejinoor sp. (H.e.) which was isolated from a saline lake in Inner Mongolia, China. Furthermore, formation mechanism and potential applications of the hydrogel as an adsorbing material are discussed.

RESULTS

Halorubrum ejinoor sp. (H.e.) cell lysate was firstly prepared by adding pure water onto the H.e. cell pellet, followed by a short incubation at 60 °C. The cell lysate was injected into different metal ion (or H⁺) solutions to obtain the hydrogel composite. It was observed that H⁺, Fe³⁺, La³⁺, Cu²⁺, and Ca²⁺ induced gelation of the cell lysate, while Fe²⁺, Co²⁺, Ni²⁺, Mg²⁺, Na⁺, and K⁺ did not. DNA and extracellular polysaccharides (EPS) in the H.e. cell lysate were found to be responsible for the gelation reaction. These results suggest that DNA and EPS should be crosslinked by metal ions (or H⁺) and form a networked structure in which the metal ion (or H⁺) serves as an anchor point. Potential application of the hydrogel as an adsorbing material was explored using La³⁺-induced H.e. hydrogel composite. The hydrogel composite can adsorb the fluoride, phosphate and DNA-binding carcinogenic agents, such as acridine orange.

CONCLUSIONS

The simplicity and cost effectiveness of the preparation method might make H.e. hydrogel a promising adsorbing material. This work is expected to expand the technical applications of haloarchaea.

Recycling of Pd(0) catalysts by magnetic nanocomposites-microbial extracellular polymeric substances@Fe3O4

Palladium (Pd) is extremely expensive due to its scarcity and excellent catalytic performance. Thus, the recovery of Pd has become increasingly important. Herein, microbial extracellular polymeric substances (EPS) and magnetic nanocomposite EPS@Fe₃O₄ were applied to recover Pd catalysts from Pd(II) wastewater. Results indicated that Pd(II) was reduced to Pd (0), which was then adsorbed by EPS (101.21 mg/g) and EPS@Fe₃O₄ (126.30 mg/(g EPS)). After adsorbing Pd, EPS@Fe₃O₄ could be collected by magnetic separation. The recovered Pd showed excellent catalytic activity in the reduction of methylene blue (MB). The pseudo-second-order kinetic model and Redlich-Peterson model best fit the adsorption results. According to spectral analysis, Pd(II) was reduced to Pd (0) by chemical groups in EPS and EPS@Fe₃O₄, and the hydroxyl had a chelating effect on adsorbed Pd. Therefore, EPS@Fe₃O₄ is an efficient adsorbent for recovering Pd from Pd(II) wastewater.

A critical review on the effects of antibiotics on anammox process in wastewater

Anaerobic ammonium oxidation (anammox) has recently become of significant interest due to its capability for cost-effective nitrogen elimination from wastewater. However, anaerobic ammonia-oxidizing bacteria (AnAOB) are sensitive to environmental changes and toxic substances. In particular, the presence of antibiotics in wastewater, which is considered unfavorable to the anammox process, has become a growing concern. Therefore, it is necessary to evaluate the effects of these inhibitors to acquire information on the applicability of the anammox process. Hence, this review summarizes our knowledge of the effects of commonly detected antibiotics in water matrices, including fluoroquinolone, macrolide, β-lactam, chloramphenicol, tetracycline, sulfonamide, glycopeptide, and aminoglycoside, on the anammox process. According to the literature, the presence of antibiotics in wastewater could partially or completely inhibit anammox reactions, in which antibiotics targeting protein synthesis or DNA replication (excluding aminoglycoside) were the most effective against the AnAOB strains.

Effects of heavy metals and metal (oxide) nanoparticles on enhanced biological phosphorus removal

With the rapid growth of economics and nanotechnology, a significant portion of the anthropogenic emissions of heavy metals and nanoparticles (NPs) enters wastewater streams and discharges to wastewater treatment plants, thereby potentially posing a risk to the bacteria that facilitate the successful operation of the enhanced biological phosphorus (P) removal (EBPR) process. Although some efforts have been made to obtain detailed insights into the effects of heavy metals and metal (oxide) nanoparticles [Me(O)NPs], many unanswered questions remain. One question is whether the toxicity of Me(O)NPs originates from the released metal ions. This review aims to holistically evaluate the effects of heavy metals and Me(O)NPs. The interactions among extracellular polymeric substances, P, and heavy metals [Me(O)NPs] are presented and discussed for the first time. The potential mechanisms of the toxicity of heavy metals [Me(O)NPs] are summarized. Additionally, mathematical models of the toxicity and removal of P, heavy metals, and Me(O)NPs are overviewed. Finally, knowledge gaps and opportunities for further study are discussed to pave the way for fully understanding the inhibition of heavy metals [Me(O)NPs] and for reducing their inhibitory effect to maximize the reliability of the EBPR process.

Effect of divalent ions on cariogenic biofilm formation

Background

Divalent cations are able to interact with exopolysaccharides (EPS) and thus are capable to modify the structure and composition of dental biofilm. At the moment, little is known about the adsorption of metals by cariogenic EPS; thus, the aim of the present study was to evaluate the effect of divalent ions (calcium, magnesium, and zinc) on the growth and biofilm formation of mutans streptococci and on the dissolution of hydroxyapatite as well as to investigate their binding to the bacterial EPS.

Results

S. mutans strains used in this study show the highest tolerance towards calcium of the ions tested. Growth parameters showed no differences to control condition for both strains up to 100 mM; revealing natural tolerance to higher concentration of calcium in the surroundings. Although excessive levels of calcium did not impair the growth parameters, it also did not have a positive effect on biofilm formation or its binding affinity to EPS. Magnesium-saturated environment proved to be counterproductive as strains were able to dissolve more Ca²⁺ from the tooth surface in the presence of magnesium, therefore releasing excessive amounts of Ca²⁺ in the environment and leading to the progression of the disease. Thus, this supports the idea of self-regulation, when more Ca²⁺ is released, more calcium is bound to the biofilm strengthening its structure and however, also less is left for remineralization. Zinc inhibited bacterial adhesion already at low concentrations and had a strong antibacterial effect on the strains as well as on calcium dissolution; leading to less biofilm and less EPS. Additionally, Zn²⁺ had almost always the lowest affinity to all EPS; thus, the unbound zinc could also still remain in the surrounding environment and keep its antimicrobial properties.

Conclusion

It is important to maintain a stable relationship between calcium, magnesium and zinc as excessive concentrations of one can easily destroy the balance between the three in cariogenic environment and lead to progression of the disease.

The complexation with proteins in extracellular polymeric substances alleviates the toxicity of Cd (II) to Chlorella vulgaris

The complexation with extracellular polymeric substances (EPS) greatly reduces the toxicity of heavy metals towards organisms in the environment. However, the molecular mechanism of EPS-metal complexation remains unclear owing to the limitation of precise analysis for key fractions and functionalities in EPS that associate with metals. Herein, we explored the EPS-Cd (II) complexation by fluorescence excitation emission matrix coupled with parallel factor (EEM-PARAFAC), two-dimensional Fourier transform infrared correlation spectroscopy (2D-FTIR-COS) and X-ray photoelectron spectroscopy (XPS), attempting to explain the mechanisms of EPS in alleviating Cd (II) toxicity toward a green alga Chlorella vulgaris (C. vulgaris). When the algal EPS were removed, the cell internalizations of Cd (II), growth inhibition rate and chlorophyll autofluorescence increased, but the surface adsorption and esterase activities decreased, indicating that the sorption of Cd (II) by EPS was crucial in alleviating the algal toxicity. Moreover, the complexation with proteins in EPS controlled the sorption of Cd (II) to algal EPS, resulting in the chemical static quenching of the proteins fluorescence by 47.69 ± 2.37%. Additionally, the complexing capability of the main functionalities, COO^- and C-OH in proteins with Cd (II) was stronger than that of C-O(H) and C-O-C in polysaccharides or C-OH in the humus-related substances. Oxygen atom in protein carboxyl C-O might be the key site of EPS-Cd (II) complexation, supported by the modified Ryan-Weber complexation model and the obvious shift of oxygen valence-electron signal. These findings provide deep insights into understanding the interaction of EPS with heavy metals in aquatic environment.

Biosorption Mechanism of Aqueous Pb2+, Cd2+, and Ni2+ Ions on Extracellular Polymeric Substances (EPS)

Heavy metal pollution has been a focus with increasing attention, especially Pb²⁺, Cd²⁺, and Ni²⁺ in an aqueous environment. The adsorption capacity and mechanism of extracellular polymeric substances (EPS) from Agrobacterium tumefaciens F2 for three heavy metals were investigated in this study. The adsorption efficiency of 94.67%, 94.41%, and 77.95% were achieved for Pb²⁺, Cd²⁺, and Ni²⁺ adsorption on EPS, respectively. The experimental data of adsorption could be well fitted by Langmuir, Freundlich, Dubinin–Radushkevich isotherm models, and pseudo-second-order kinetic model. Model parameters analysis demonstrated the great adsorption efficiency of EPS, especially for Pb²⁺, and chemisorption was the rate-limiting step during the adsorption process. The functional groups of C=O of carboxyl and C-O-C from sugar derivatives in EPS played the major role in the adsorption process judged by FTIR. In addition, 3D-EEM spectra indicated that tyrosine also assisted EPS adsorption for three heavy metals. But EPS from strain F2 used the almost identical adsorption mechanism for three kinds of divalent ions of heavy metals, so the adsorption efficiency difference of Pb²⁺, Cd²⁺, and Ni²⁺ on EPS could be correlated to the inherent characteristics of each heavy metal. This study gave the evidence that EPS has a great application potential as a bioadsorbent in the treatment of heavy metals pollution.

The roles of extracellular polymeric substances of Pandoraea sp. XY-2 in the removal of tetracycline

In this study, the roles of extracellular polymeric substances (EPSs) excreted by Pandoraea sp. XY-2 in the removal of tetracycline (TC) were investigated. In the early stage, TC in the solution was mainly removed by the adsorption of EPSs, which accounted for 20% of TC. Thereafter, large amount of TC was transported into the intracellular and biodegraded. EPSs was extracted and the contents of polyprotein and polysaccharides reached their maximum values (30.84 mg/g and 11.15 mg/g) in the first four days. Fourier transform infrared spectroscopy analysis revealed that hydroxyl, methylidyne, methylene and amide I groups in EPSs participated in the adsorption of TC. Furthermore, three-dimensional excitation-emission matrix fluorescence spectroscopy analysis revealed that TC caused the quenching of EPSs fluorescent groups. The quenching mechanism was attributed to static quenching and protein-like substances in EPSs from Pandoraea sp. XY-2 dominated the TC adsorption process. Bioinformatic analysis of Pandoraea sp. XY-2 genome identified multiple genes involved in exopolysaccharide synthesis and EPSs formation. The insights gained in this study might provide a better understanding about the adsorption process of EPSs in tetracycline-contaminated environment.

Phytoremediation of heavy metals by four aquatic macrophytes and their potential use as contamination indicators: a comparative assessment

The present study estimated the ability of four aquatic macrophytes (Eichhornia crassipes (Mart.) Solms, Ludwigia stolonifera (Guill. & Perr.) P.H. Raven, Echinochloa stagnina (Retz.) P. Beauv. and Phragmites australis (Cav.) Trin. ex Steud.) to accumulate Cd, Ni and Pb and their use for indicating and phytoremediating these metals in contaminated wetlands. Three sites at five locations in the Kitchener Drain in Gharbia and Kafr El-Sheikh Governorates (Egypt) were selected for plant, water and sediment sampling. The water in the Kitchener Drain was polluted with Cd, while Pb and Ni were far below the maximum level of Pb and Ni in the irrigation water. In comparison to the other species, P. australis accumulated the highest concentrations of Cd and Ni, while E. crassipes accumulated the highest concentration of Pb in its tissues. The four species had bioaccumulation factors (BAFs) greater than one, while their translocation factors (TFs) were less than 1 for most heavy metals, except Cd in the leaf and stem of E. stagnina and L. stolonifera, respectively, and Ni in the stem and leaf of E. stagnina. The BAF and TF results indicated that the studied species are suitable for phytostabilizing the studied heavy metals, except Ni in E. stagnina and Cd in L. stolonifera, which are suitable for phytoextracting these metals. Significant positive correlations were found between the investigated heavy metals in the water or sediment and the plant tissues. Their high BAFs, with significant proportional correlations, supported the potential of these species to serve as bioindicators and biomonitors of heavy metals in general and in the investigated metals specifically.

A novel amphiphilic oligopeptide induced the intrafibrillar mineralisation via interacting with collagen and minerals

Mineralised collagen fibrils constitute the basic building blocks of bone, dentin and cementum. Noncollagenous proteins (NCPs) that are indispensable for collagen biomineralisation are not commercially available, and the mechanism of intrafibrillar mineralisation remains debatable. Herein, synthetic biomimetic molecules are regarded as alternative candidates for NCPs, and more convenient in revealing the mechanism of intrafibrillar mineralisation in vitro. Here, we fabricated a novel amphiphilic oligopeptide imitating a natural NCP. We aimed to investigate the effectiveness of the oligopeptide in intrafibrillar mineralisation and partially reveal the corresponding mechanism in vitro. The effectiveness of the oligopeptide in intrafibrillar mineralisation was characterised from the following aspects: (1) mineral interaction, (2) collagen binding and (3) induction of intrafibrillar mineralisation. Results indicated that the self-assembled oligopeptide could attract calcium ions inducing the formation of amorphous precursors; and bind onto the surface of collagen fibrils. These processes were mainly driven by the electrostatic attraction and hydrogen bonds. The self-assembled oligopeptide induced the intrafibrillar mineralisation of reconstituted collagen fibrils, in which the c-axis of apatite crystallites was roughly parallel to the long axis of the fibrils. The collagen mineralisation was achieved by binding with the self-assembled oligopeptide to increase the pool of mineralization precursors available for intrafibrillar mineralisation. In addition, the self-assembled oligopeptide induced dentin collagen remineralisation and formed a 30 μm-thick remineralised layer within 96 h. Our work sheds light on the fabrication of a novel biomimetic molecule for collagen mineralisation. The results should serve as a reference for understanding the mechanism of intrafibrillar mineralisation.

Interactions between tetracycline and extracellular polymeric substances in anammox granular sludge

The effects of antibiotics on extracellular polymeric substances (EPS) using tetracycline as the model chemical were analyzed in terms of molecular property and structure. Results showed that three components, tryptophan, tryptophan type-proteins and polysaccharides in EPS of granular sludge from anaerobic ammonium oxidation (anammox) reactor can interacted with tetracycline, detected by the static quenching via the endogenous fluorescence quenching and transient fluorescence spectroscopy. Thermodynamic experiment confirmed that their interaction was dominated by the hydrophobic force. Combined with the synchronous fluorescence spectroscopy, it was found that tetracycline facilitated the extension degree of peptide chains in tryptophan type-proteins, leading to the enhancement of hydrodynamic diameter of the macromolecules in EPS when binding with tetracycline. EPS in AnGS demonstrated the resistance ability to tetracycline by converting from gel to sol state in rheological term. With the increase of tetracycline concentration, the stability of elastic structures in EPS declined, influencing the AnGS stability.

Exploration of the reduction mechanism of Cr(VI) in anaerobic hydrogen fermenter

The bio-reduction of hexavalent chromium (Cr(VI)) by anaerobic fermentation is considered as a promising, low-cost and environment-friendly way. However, it is unclear for the reduction mechanisms of Cr(VI) in an anaerobic hydrogen fermenter, such as reduction kinetics, related electron donors, migration and transformation, reduction site and key components, and related microorganisms. To clarify these issues, a hydrogen fermenter was designed to reduce Cr(VI) at 55 °C with glucose as initial substrate. Results show that 100 mg/L Cr(VI) can be completely reduced (99.5%) to trivalent chromium (Cr(III) through chemical and biological reactions. Bio-reduction dominates Cr(VI) removal in a first-order exponential decay mode with both glucose and its metabolites (volatile fatty acids) as electron donors. Moreover, volatile fatty acids are more suitable as electron donors for Cr(VI) bio-reduction than glucose. Bacilli, Clostridia and Thermotogae in the fermenter dominated the reduction of Cr(VI) by regulating the production and composition of extracellular polymers (EPSs), in which carboxyl and hydroxyl groups play an important role for Cr(VI) reduction by coordination. The results can guide us to regulate the bio-reduction of Cr(VI), and provide reference for the development of bio-reduction technology of Cr(VI).

Adsorption behaviors of Cu2+, Zn2+ and Cd2+ onto proteins, humic acid, and polysaccharides extracted from sludge EPS: Sorption properties and mechanisms

To clarify the adsorption behaviors of typical heavy metals onto sludge extracellular polymeric substances (EPS), the adsorption capacities and mechanisms, as well as the contributions of the different EPS components (proteins, humic acids and polysaccharides), to the adsorption of Zn²⁺, Cu²⁺ and Cd²⁺ were separately explored. Overall, proteins exhibited a relatively high adsorption capacity for the three metals ions, followed by humic acid, whereas least for polysaccharides. The adsorption of Cu²⁺ and Cd²⁺ onto proteins, humic acid and polysaccharides fit well to the Freundlich isotherm, whereas Langmuir model was the best fit for Zn²⁺ bindings onto polysaccharides/humic acid. The binding of Cu²⁺, Zn²⁺ and Cd²⁺ onto the three EPS components was exothermically favorable, and significant electrostatic interactions were observed for the heavy metals sorption onto humic acid and proteins. In addition, the effect of metal ions sorption on the spectrum of the proteins, polysaccharides and humic acid was also explored.

Phytostabilization as a phytoremediation strategy for mitigating water pollutants by the floating macrophyte Ludwigia stolonifera (Guill. & Perr.) P.H. Raven

The present study evaluated the phytoremediation potential of the floating macrophyte Ludwigia stolonifera for removing trace metals from contaminated water bodies. Forty quadrats, distributed equally in eight sites (six polluted two unpolluted sites) were selected seasonally for water, sediment and plant investigations. The leaf area, fresh and dry biomass, chlorophyll b and carotenoids contents of L. stolonifera were significantly reduced in polluted sites. L. stolonifera plants accumulated concentrations of the investigated trace metals in their roots higher than the shoots. The roots contributed to the highest concentrations of Al and Cu during spring; Fe, Mn and Ni during summer; Cd and Zn during autumn; and Cr and Pb during winter. Compared to the unpolluted sites, the below- and above-ground parts from the polluted sites accumulated higher concentrations of most investigated trace metals, except Fe. The below-ground parts of L. stolonifera had high seasonal potential for seasonal accumulation of Cd, Cu, Ni, Zn and Pb with a bioaccumulation factor that exceeded 1, the translocation factor of the investigated metals was <1. Therefore, the study species is suitable for metals phytostabilization and thus can be considered a potential phytoremediator of these metals.