Interaction Of Extracellular Polymeric Substances Research Articles

Impact of Hydroxy-Aluminum and Extracellular polymeric substances interactions on waste activated sludge Dewatering: A molecular perspective

Al13 and Al30 are the dominant aluminum (Al) species in polyaluminium chloride commonly used for sludge dewatering. However, the presence of extracellular polymeric substances (EPS) in the waste activated sludge hinders the coagulation effectiveness of Al-based coagulants. This study focused on the effects and mechanisms of Al13 and Al30 on treating sludge EPS. From a bulk perspective, the dosing of two coagulants significantly reduced the dissolved organic carbon and various organic compounds, reflecting their efficacy in removing organic substances in EPS. Further molecular characterization was revealed by FT-ICR MS. Al13 was more effective in removing lipids, lignins, and sulfur-containing compounds compared to Al30. Al13 also demonstrated a pronounced removal in components enriched in oxygen atoms (10–20) and KMD(COO) (0.5–0.7), suggesting its ability to remove molecules across a broader range of unsaturation. After coagulation with Al13, the areas corresponding to Al2p1/2 and Al2p2/3 in the Al2p spectra were more prominent compared to those in the Al30-coagulated EPS. Therefore, Al13 can both remove complex and low molecule weight compounds through abound forms of adsorption sites, making it more efficient in releasing bound water compared to Al30.

Algal EPS modifies the toxicity potential of the mixture of polystyrene nanoplastics (PSNPs) and triphenyl phosphate in freshwater microalgae Chlorella sp.

Triphenyl phosphate (TPP) and polystyrene nanoplastics (PSNPs) are prevalent freshwater contaminants obtained mainly from food packaging, textiles and electronics. Algal extracellular polymeric substances (EPS), a part of natural organic matter, may influence these pollutants' behaviour and toxicity. The presence of EPS can enhance the aggregation of TPP-PSNP mixtures, and reduce the bioavailability, and thus the toxicity potential. Understanding the mutual interactions between TPP, PSNPs, and EPS in the aquatic environment is a prerequisite for the environmental risk assessment of these chemicals. The study examines the toxicity effects of various surface-modified PSNPs (1 mg/L of plain, animated, and carboxylated) and TPP (0.05, 0.5, and 5 mg/L) in pristine and combined forms on freshwater microalgae, Chlorella sp., as a model organism. The physical-chemical interactions of algal EPS (10 mg/L) with PSNPs and TPP and their mixtures were studied. The toxicity potential of the PSNPs was estimated by quantifying growth inhibition, oxidative stress, antioxidant activity, and photosynthesis in the cells. TPP toxicity increased in the presence of the PSNPs, however the addition of algal EPS reduced the combined toxic effects. EPS plays a protective role by reducing oxidative stress and enhancing photosynthetic efficiency in the algal cells. The Pearson modeling analysis indicated a positive correlation between growth inhibition, and reactive oxygen species, malondialdehyde production. The cluster heatmap and correlation mapping revealed a strong correlation among the oxidative stress, growth inhibition, and photosynthetic parameters. The study clearly highlights the potential of EPS in mitigating the risk of mixed emerging pollutants in the aquatic environment.

Transport and interaction of cadmium and active sludge extracellular polymeric substances in saturated sand influenced by ionic strength and composition.

Artificial groundwater recharge with reclaimed water (secondary effluent from wastewater treatment plants) has become an important approach to solving water scarcity worldwide. Microorganisms in activated sludge can secrete many extracellular polymeric substances (EPS). However, information on the impact of EPS on the movement of heavy metals in porous media and their environmental effects on underground networks is limited. To assess this risk, we extracted EPS from the aerobic section of a wastewater treatment plant using hot sodium hydroxide and conducted experiments using one-dimensional sand columns to investigate how ion composition and strength affect the movement and interaction of cadmium (Cd) and EPS in porous media. The results showed that EPS facilitated Cd migration in porous media. Sodium (Na) and calcium (Ca) ions promoted the migration of Cd in porous media and EPS-Cd complexation. The effect of Ca was more significant than that of Na. As the Na adsorption ratio increased, the migration ability of Cd in porous media and the complexation ability of EPS with Cd decreased. Therefore, when estimating the migration of EPS and Cd in subsurface environments, careful consideration should be given to prevent the risk of groundwater pollution.

Effects of extracellular polymeric substances on silver nanoparticle bioaccumulation and toxicity to Triticum aestivum L.

The potential effects of extracellular polymeric substances (EPS) on the behavior and toxicity of silver nanoparticle (Ag-NPs) and silver sulfide nanoparticle (Ag2S-NPs) remains ambiguous. The interaction of EPS from Bacillus subtilis with Ag2S-NPs, metallic Ag-NPs, or ionic Ag, and the associated plant safety had been examined in this study. The biological impacts of Ag-NPs and Ag2S-NPs were Ag form-dependent and highly influenced by microbial EPS. Compared with metallic Ag-NPs, Ag2S-NPs exert inert biological impacts, as revealed by 3.44 times lower Ag bioaccumulation in wheat (Triticum aestivum L.) seedlings and nearly reduce plant biomass when wheat was subjected to 1.0 mg-Ag L−1 of Ag-NPs and Ag2S-NPs with the transfer factors of 151.56–930.87 vs. 12.52–131.81, respectively. These observations were coincident with the low dissolved Ag ([Ag]diss) in the Ag2S-NPs treatment than the Ag-NPs treatment (114.0 vs. 0.0791, μg L−1). Compared with the enhanced toxicity of Ag2S-NPs to wheat, Bacillus subtilis EPS significantly alleviate the phytotoxicity of Ag-NPs, as revealed by the relative root elongation (7.15–45.40% decrease vs. 2.39–11.75% increase), and malondialdehyde (1.47–83.22% increase vs. 8.57–25.25% decrease) and H2O2 (11.27–71.78% increase vs. 5.16–36.67% decrease) contents. These constrasting plant responses of B. subtilis EPS are mainly caused by their complexation property with toxic Ag+ and nutrient elements for wheat stressed by Ag-NPs and Ag2S-NPs, respectively. Our findings highlight the importance of rhizospheric EPS in affecting the biogeochemistry and ecotoxicity of metal nanoparticles including Ag-NPs and Ag2S-NPs in agricultural systems.

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) (10-50mgL-1) and selenite (79mgL-1) for 300days at pH7.3 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 > 100kDa 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 < 10kDa. The fingerprint of the humic-like substances showed emergence of a new peak with aMW of 13 to 300kDa 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.

Unraveling the capability of graphene nanosheets and γ-Fe2O3 nanoparticles to stimulate anammox granular sludge

In this study, we investigated the potentials of nanomaterials to enhance anaerobic ammonium oxidation (anammox) process, in terms of nitrogen removal, microbial enrichment, and activity of key enzymes. Graphene nanosheets (GNs) and γ-Fe2O3 nanoparticles (NPs) were selected due to their catalytic functions as conductive material and electron shuttles, respectively. The obtained results revealed that the optimum dosage of GNs (10 mg/L) boosted the nitrogen removal rate (NRR) by 46 ± 3.1% compared to the control, with maximum NH4+-N and NO2−-N removal of 86.5 ± 2.7% and 97.1 ± 0.5%, respectively. Moreover, hydrazine dehydrogenase (HDH) enzyme activity was augmented by 1.1-fold when using 10 mg/L GNs. The presence of GNs promoted the anammox granulation via enhancement of hydrophobic interaction of extracellular polymeric substances (EPS). Regarding the use of γ-Fe2O3 NPs, 100 mg/L dose increased NRR by 55 ± 3.8%; however, no contribution to HDH enzyme activity and a decrease in EPS compositions were observed. Given that the abiotic use of γ-Fe2O3 NPs further resulted in high adsorption efficiency (~92%), we conclude that the observed promotion due to γ-Fe2O3 NPs was mainly abiotic. Moreover, the 16S rRNA analysis revealed that the relative abundance of genus C. Jettenia (anammox related bacteria) increased from 11.9% to 12.3% when using 10 mg/L GNs, while declined to 8.3% at 100 mg/L γ-Fe2O3 NPs. Eventually, nanomaterials could stimulate the efficiency of anammox process, and this promotion and associated mechanism depend on their dose and composition.

Influence of metals and metalloids on the composition and fluorescence quenching of the extracellular polymeric substances produced by the polymorphic fungus Aureobasidium pullulans

Aureobasidium pullulans is a ubiquitous and widely distributed fungus in the environment, and exhibits substantial tolerance against toxic metals. However, the interactions between metals and metalloids with the copious extracellular polymeric substances (EPS) produced by A. pullulans and possible relationships to tolerance are not well understood. In this study, it was found that mercury (Hg) and selenium (Se), as selenite, not only significantly inhibited growth of A. pullulans but also affected the composition of produced EPS. Lead (Pb) showed little influence on EPS yield or composition. The interactions of EPS from A. pullulans with the tested metals and metalloids depended on the specific element and their concentration. Fluorescence intensity measurements of the EPS showed that the presence of metal(loid)s stimulated the production of extracellular tryptophan-like and aromatic protein-like substances. Examination of fluorescence quenching and calculation of binding constants revealed that the fluorescence quenching process for Hg; arsenic (As), as arsenite; and Pb to EPS were mainly governed by static quenching which resulted in the formation of a stable non-fluorescent complexes between the EPS and metal(loid)s. Se showed no significant interaction with the EPS according to fluorescence quenching. These results provide further understanding of the interactions between metals and metalloids and EPS produced by fungi and their contribution to metal(loid) tolerance.Key points• Metal(loid)s enhanced production of tryptophan- and aromatic protein-like substances.• Non-fluorescent complexes formed between the EPS and tested metal(loid)s.• EPS complexation and binding of metal(loid)s was dependent on the tested element.• Metal(loid)-induced changes in EPS composition contributed to metal(loid) tolerance.

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.

Efficient removal of disinfection by-products precursors and inhibition of bacterial detachment by strong interaction of EPS with coconut shell activated carbon in ozone/biofiltration

The change of water quality was investigated in pilot-scale ozone-biological activated carbon (O3-BAC) filters using an emerging coconut shell-based granular activated carbon (CAC) or traditional granular activated carbon (GAC), respectively. More dissolved organic carbon (DOC) and disinfection by-products (DBPs) precursors were removed, meanwhile, less microbes, less metabolites and smaller microbial clusters were detected in the effluent of CAC compared with GAC. Sequentially, lower DBPs formation and higher disinfection efficiency were achieved in drinking water distribution systems (DWDSs). Furthermore, it was observed that extracellular electron transfer was enhanced in the attached biofilms of CAC, hence improving the microbial metabolic activity and biological removal of DOC. The results were attributed to the strong interaction of extracellular polymeric substances (EPS) with highly graphitized CAC. In addition, CAC resulted in totally different EPS in attached biofilms with superior characteristics including stronger viscosity, higher flocculating efficiency, mechanical stability and numerous binding sites for bacterial cells. Consequently, a wide range of compact interconnected biofilms formed on the surface of CAC and exhibited certain binding effect for microbial flocs and metabolites. Therefore, CAC resulted in higher microbial metabolic activity and lower release of microbes and metabolites, which was beneficial to maintain water quality safety in downstream DWDSs.

An electrokinetic perspective into the mechanism of divalent and trivalent cation sorption by extracellular polymeric substances of Pseudomonas fluorescens

Extracellular polymeric substances (EPS) contain a vast number of functional groups which can provide sorption sites for heavy metal cations in solution, however, the mechanisms for the interaction of EPS with various metal cations were not well understood. In this study, the sorption potential of EPS from Pseudomonas fluorescens for different cations was investigated. The changes of electrokinetic properties that occurred on the surface of EPS once they adsorbed these cations were also studied using zeta potential measurements as a function of pH and cation concentration. The adsorption data fitted Freundlich isotherm better than Langmuir and D–R isotherms. The interactions of the cations with EPS were favourable with the separation factor Kr < 1. Under different pH conditions, the zeta potential of EPS in the different cation solution followed the order: Fe(III) (at pH ≤ 5.0) > Al(III) > Cu(II) > Mn(II) > Ni(II)≈Cd(II) > Ca(II) > EPS, while with respect to the initial cation concentration, the zeta potential of EPS was in the order: Fe(III) > Al(III) > Cu(II) > Cd(II) > Ni(II)≈Mn(II)≈Ca(II). The effect of cation sorption on the surface charge of EPS increased with pH as well as cation concentration. The thermodynamic analysis demonstrated that besides the sorption of Fe which was exothermic, all the other cations were adsorbed through an endothermic process. The ΔSads revealed that most of the cations interacted with EPS through the formation of inner-sphere complexes. The ATR-FTIR analyses confirmed that complexation occurred between the cations and functional groups on the surface of EPS. The zeta potential of EPS shifted to positive value direction due to sorption of cations on EPS, indicating that the specific interactions were involved in the sorption process. This study enhances our understanding of EPS aggregation and heavy metal bio-sorption through the electrokinetic mechanism. The results will provide useful references for immobilization of heavy metals and alleviation of Al toxicity in acidic soils.

Enhanced “contact mechanism” for interaction of extracellular polymeric substances with low-grade copper-bearing sulfide ore in bioleaching by moderately thermophilic Acidithiobacillus caldus

In order to enhance the “contact mechanism” governing the interaction of extracellular polymeric substances (EPS) with low-grade copper-bearing sulfide ore for the bioleaching of copper, moderately thermophilic Acidithiobacillus caldus was subjected to exogenous intervention with iron and sulfur. The enhancement of the contact mechanism was systematically investigated by evaluating the attached cells/EPS dynamics, intracellular adenosine triphosphate (ATP), cell functional groups, gene transcriptional level, and ore characteristics. Confocal laser scanning microscopy (CLSM) revealed that exogenous intervention with iron and sulfur led to the production of a denser EPS layer and faster adsorption of the attached cells to the ore based on differential fluorescence staining, which indicated enhancement of the “contact mechanism”. The increased intracellular ATP content of the attached cells in the exogenous substrate system provided the required energy for the adsorption processes associated with the “contact mechanism”. Fourier-transform infrared spectroscopic (FTIR) analysis of the attached cells and the ore showed a dramatic shift of the NH and COS peaks (associated with EPS formation), whereas the FTIR peaks of SO and SO42− associated with sulfur metabolism were also significantly influenced. Moreover, reverse transcription polymerase chain reaction (RT-PCR) analysis revealed that the expression of genes related to cellular energy metabolism (nuoB, nuoC, atpE, atpF), sulfur metabolism (sor, sqr, sdo, soxA), biofilm formation (pgaA, pgaB), and cell colonization (acfA, acfB, acfC, acfD) was up-regulated after exogenous intervention, verifying enhancement of the “contact mechanism” at the transcriptional level. In addition, scanning electron microscopy (SEM) indicated more obvious adsorption traces on the ore surface. X-ray diffraction (XRD) indicated the presence of more complex derivatives, such as Fe3(SO4)4, FeSO4, Fe2(SO4)3, and Cu2S, which is suggestive of more active iron/sulfur metabolism with addition of the exogenous iron and sulfur. Overall, a model for bioleaching of low-grade copper-bearing sulfide ore by moderately thermophilic A. caldus was constructed. The results of this investigation should provide a guide for similar industrial bioleaching processes.

Mechanism of Cu(II) and Cd(II) immobilization by extracellular polymeric substances (Escherichia coli) on variable charge soils

Extracellular polymeric substances (EPS) found in soils can reduce the mobility of heavy metals through the use of both electrostatic and non-electrostatic mechanisms. Their effects vary from one soil type to another. The influence of EPS from Escherichia coli on the adsorption behaviors of Cu(II) and Cd(II) by two bulk variable charge soils, Oxisol and Ultisol, was studied at constant and varied pH, and the results were compared to a constant charge Alfisol. The maximum adsorption capacities of the soils were significantly (P < 0.05) enhanced in the presence of EPS, with Cu(II) adsorption being greater. Interaction of EPS with soils made the soil surface charge more negative by neutralizing positive charges and shifting the zeta potentials in a negative direction: from −18.6 to −26.4 mV for Alfisol, +5.1 to −22.2 mV for Oxisol, and +0.3 to −28.0 mV for Ultisol at pH 5.0. The adsorption data fitted both the Freundlich and Langmuir isotherms well. Preadsorbed Cd(II) was more easily desorbed by KNO3 than preadsorbed Cu(II) from both the control and EPS treated soils. The adsorption of both metals was governed by electrostatic and non-electrostatic mechanisms, although more Cu(II) was adsorbed through the non-electrostatic mechanism. The information obtained in this study will improve our understanding of the mechanisms involved in reducing heavy metals mobility in variable charge soils and hence, their bioavailability.

Interactions of EPS with soil minerals: A combination study by ITC and CLSM

The adsorption of extracellular polymeric substances (EPS) from Pseudomonas putida on montmorillonite, kaolinite and goethite was investigated as a function of pH using batch studies coupled with confocal laser scanning microscopy (CLSM) and isothermal titration calorimetry (ITC). Characterization by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy showed that the extracted EPS contained carboxyl, phosphoryl, amino, and hydroxyl on functional groups as well as polysaccharides, protein and nucleic acid on components. The mass fraction of EPS adsorption on minerals decreased with the final pH increased from 3.0 to 9.0. The mass fraction of EPS-N adsorption varied with pH values and was higher than that of EPS-C or EPS-P on montmorillonite and kaolinite, while the mass fraction of EPS-P adsorption was the highest on goethite. CLSM results further demonstrated that proteins were predominantly distributed on the montmorillonite and kaolinite surfaces, while nucleic acids were mainly on the goethite surface. ITC results revealed that the adsorption process in all mineral systems was exothermic, and pH altered the heat effect of EPS-mineral reactions. The data obtained in this study would facilitate a better understanding of the adsorption mechanisms of EPS on minerals.

Multiple EPS interactions involved in the cohesion and structure of aerobic granules

This study aims to clarify the biochemical nature and interactions of Extracellular Polymeric Substances (EPS) involved in the structure and cohesive properties of aerobic granules. Granules were incubated with selective hydrolytic enzymes or with chemicals and the resistance of digested granules to shear stress was evaluated. After α-amylase digestion, the hydrodynamic stress released macro-particles (>315μm) while soluble molecules (<1.5μm) and micro-particles (1.5–315μm) where mainly recovered after savinase and EDTA treatments. These data show that α (1–4) glucans and proteins are key polymers for granule cohesion and that divalent cationic bridging is a major aggregative mechanism.On the basis of these experiments and microscopy observations, a model is proposed for the spatial organization of EPS in the granular structure, in which α glucans are arranged in a capsular layer surrounding bacterial clusters while anionic proteins constitute the intercellular cement that may reinforce cohesion inside the bacterial clusters.

Interaction between Enrofloxacin and the Extracellular Polymeric Substances from Platymonas Subcordiformis

Extracellular polymeric substances (EPS) in marine algae-Platymonas subcordiformisaffected by enrofloxacin (ENR), the typical quinolone antibiotics released to the environment through different ways, was studied. A 3-dimension EEM (excitation –emission matrix) fluorescence spectroscopy was used to examine the interaction between EPS and ENR, and the fluorescent peaks A and B were detected, whose fluorescence intensity remarkably decreased with the increased ENR concentration. It was demonstrated that the interaction of EPS with ENR well fitted the modified Stern-Volmer. It was concluded that the presence of EPS in marine algae affected the transport and transform of antibiotics in aquatic environment.

Effects of silver nanoparticles on wastewater biofilms

The goal of this research is to understand the potential antibacterial effect of silver nanoparticles (Ag-NPs) on biological wastewater treatment processes. It was found that original wastewater biofilms are highly tolerant to the Ag-NP treatment. With an application of 200 mg Ag/L Ag-NPs, the reduction of biofilm bacteria measured by heterotrophic plate counts was insignificant after 24 h. After the removal of loosely bound extracellular polymeric substances (EPS), the viability of wastewater biofilms was reduced when treated under the same conditions. By contrast, when treated as planktonic pure culture, bacteria isolated from the wastewater biofilms were highly vulnerable to Ag-NPs. With a similar initial cell density, most bacteria died within 1 h with the application of 1 mg Ag/L Ag-NPs. The results obtained here indicate that EPS and microbial community interactions in the biofilms play important roles in controlling the antimicrobial effects of Ag-NPs. In addition, slow growth rates may enhance the tolerance of certain bacteria to Ag-NPs. The effects of Ag-NPs on the entire microbial community in wastewater biofilms were analyzed using polymerase chain reaction–denaturing gradient gel electrophoresis, PCR–DGGE. The studies showed that the microbial susceptibility to Ag-NPs is different for each microorganism. For instance, Thiotrichales is more sensitive to Ag-NPs than other biofilm bacteria.

Distinct roles of extracellular polymeric substances in Pseudomonas aeruginosa biofilm development

Bacteria form surface attached biofilm communities as one of the most important survival strategies in nature. Biofilms consist of water, bacterial cells and a wide range of self-generated extracellular polymeric substances (EPS). Biofilm formation is a dynamic self-assembly process and several distinguishable stages are observed during bacterial biofilm development. Biofilm formation is shown to be coordinated by EPS production, cell migration, subpopulation differentiation and interactions. However, the ways these different factors affect each other and contribute to community structural differentiation remain largely unknown. The distinct roles of different EPS have been addressed in the present report. Both Pel and Psl polysaccharides are required for type IV pilus-independent microcolony formation in the initial stages of biofilm formation by Pseudomonas aeruginosa PAO1. Both Pel and Psl polysaccharides are also essential for subpopulation interactions and macrocolony formation in the later stages of P. aeruginosa PAO1 biofilm formation. Pel and Psl polysaccharides have different impacts on Pseudomonas quinolone signal-mediated extracellular DNA release in P. aeruginosa PAO1 biofilms. Psl polysaccharide is more important than Pel polysaccharide in P. aeruginosa PAO1 biofilm formation and antibiotic resistance. Our study thus suggests that different EPS materials play distinct roles during bacterial biofilm formation.

Assessment of metal - extracellular polymeric substances interactions by asymmetrical flow field-flow fractionation coupled to inductively coupled plasma mass spectrometry

Environmental context. Extracellular polymeric substances (EPS) are soluble polymers that are liberated from microorganisms and represent an important component of the natural organic matter in the aquatic and terrestrial environment. These substances affect nutrient and toxic metal cycling, both owing to their metal binding properties and their effect on aggregation and sedimentation. In order to obtain more information on their role in metal transport, EPS size (molar mass) distributions and the associated Ca, Cd and Pb were measured by using asymmetrical flow field-flow fractionation coupled to inductively coupled plasma mass spectrometry. Abstract. Extracellular polymeric substances (EPSs) excreted by the bacterium Sinorhizobium meliloti and associated Ca, Cd and Pb were characterised by asymmetrical flow field-flow fractionation coupled with UV spectrophotometry and inductively coupled plasma mass spectrometry in terms of molar-mass distributions, number- and weight-average molar masses and polydispersity index. Two major populations with weight-average molar masses of 74 × 103 and 1.35 × 106 g mol–1 were obtained for the EPS. Characterisation of the whole EPS–metal interactions evidenced the preferential binding of Ca and Cd to the low molar mass fraction, whereas Pb associated mainly with the high molar mass (HMM) fraction. Comparison with the EPS produced by exoY-mutant, deficient in HMM-EPS excretion, confirmed the preferential binding of Pb to the high molar mass fraction. Enrichment of the EPS with increasing metal concentrations induced the formation of aggregates, which was most pronounced in the presence of 10–4 mol L–1 Pb.

Complexation between Hg(II) and biofilm extracellular polymeric substances: An application of fluorescence spectroscopy

The three-dimensional excitation emission matrix (EEM) fluorescence spectroscopy was employed to investigate the interaction of extracellular polymeric substances (EPS) from natural biofilm with Hg(II). The EEM spectra demonstrated that EPS with molecular weight over 14 kDa had two protein-like fluorescence peaks. The fluorescence intensity at both peaks was strongly dependent on the solution pH in the absence and presence of Hg(II), with the maximal fluorescence intensity at neutral pH. Fluorescence of both protein-like peaks was significantly quenched by Hg(II). The values of conditional stability constants (log K(a)=3.28-4.48) derived from modified Stern-Volmer equation are approximate to those for humic substances and dissolved organic matter (DOM), indicating that fluorescent components in EPS have strong binding capacity for Hg(II). Our findings suggest that EPS from biofilm is a class of important organic ligands for complexation with Hg(II) and may significantly affect the chemical forms, mobility, bioavailability and ecotoxicity of heavy metals in the aquatic environment.

Utilizing QCM-D To Characterize the Adhesive Mucilage Secreted by Two Marine Diatom Species in-Situ and in Real-Time

The quartz crystal microbalance with dissipation monitoring (QCM-D) was used to monitor the deposition of adhesive extracellular polymeric substances (EPS) employed by the marine biofouling diatoms Craspedostauros australis Cox and Amphora coffeaeformis Cleve during initial adhesion and subsequent motility. Upon injection into the QCM chamber, initial negative frequency (f) shifts and positive dissipation (D) shifts were measured that correlated to cells impacting and adhering to the QCM sensor surface. Following this "initial adhesion" response, f continued to decrease while D increased logarithmically. Rather than the result of any cell morphological alterations at the substrate surface, the shifts were correlated to the time-dependent deposition of EPS upon the substrate surface as a result of cellular motility, or gliding. Experiments utilizing comparable cell concentrations of the diatom species C. australis and A. coffeaeformis revealed significant differences between the parameter responses recorded, where A. coffeaeformis produced Deltaf and DeltaD values of -32 Hz and 6.6, and C. australis produced values of -82 Hz and 42, respectively, after 20 h post-inoculation. The viscoelastic properties of the adhered EPS adlayer from both species were examined via a Deltaf/DeltaD plot, providing reproducible signature "ratio" values for each species that likely correlate to differences in EPS interactions with the substrate that may be associated directly to differences in the fouling potential of the two species. There is a distinct lack of knowledge regarding the chemical nature of the adhesive polymers engaged, and few quantitative techniques are applicable to the study of diatom EPS. We propose that QCM-D may be a useful tool in identifying differences in the EPS employed by diatoms of different fouling potential.