Functional Groups Of Extracellular Polymeric Substances Research Articles

Insights into the interaction between mineral formation and heavy metals immobilization, mediated by Virgibacillus exopolymeric substances

Heavy metal pollution poses significant risks to both the environment and human health due to their toxicity, long residence times, and their ability to bioaccumulate and bio magnify across the food chain. To address this issue, microbial biomineralization has emerged as a promising approach to the bio-removal of heavy metals through immobilization. This process is facilitated by extracellular polymeric substances (EPS), which also play a crucial role in mediating mineral formation. In this study, the interactions between several selected heavy metals (Cd2+, Cu2+, Ni2+, Zn2+), EPS, and mineral formation were investigated using two mineral-forming Virgibacillus strains isolated from the Qatari sabkhas, which are known to be suitable sites for the formation of biominerals. An additional non-mineral-forming Virgibacillus strain isolated from the Dukhan oil waste dumpsite was also investigated. Cd2+ and Zn2+ were to inhibit mineral formation, likely due to competition with Ca2+ and Mg2+ ions during biomineralization. However, exposure to Ni2+ or Cu2+ resulted in changes in the FTIR spectra of the EPS, suggesting the presence of specific functional group bindings within the EPS matrix. The EPS produced by each strain was also directly associated with their efficiency (%) at removing heavy metals. Notably, the EPS from Virgibacillus halodenitrificans Z4D1, the non-mineral-forming strain, exhibited the highest heavy metal removal efficiency of 31.7 % for Zn2+. These findings reveal that EPS do not only affect the biomineralization process but also that the functional groups in EPS have a direct effect on the immobilization of several heavy metals. Conditions that are not suitable for mineral formation may instead be appropriate for the removal of specific heavy metals.

Insights into the membrane fouling aggravation under polyethylene terephthalate microplastics contamination: From a biochemical point of view

This study evaluated the potential effects of polyethylene terephthalate microplastics (PET-MPs) on a membrane bioreactor. The results showed that 10–30 mg/L PET-MPs exposure showed a minor effect on reactor performances, while 50 mg/L PET-MPs significantly decreased the chemical oxygen demand and NH4+-N removal efficiencies. Long-term PET-MPs exposure resulted in sludge foaming, and significantly increased extracellular polymeric substances (EPS) contents from 463.08 ± 62.42 to 952.54 ± 23.67 mg/m2, which was the main factor in triggering severe membrane fouling. Excitation emission matrix and Fourier transform infrared spectroscopic analysis revealed significant changes in fluorescence properties and functional groups of EPS. Particularly, protein secondary structure analysis indicated that high abundant β-sheet facilitated the exposure of inner hydrophobic groups of bacterial cells and EPS, and consequently enhanced the interfacial interactions of foulants-foulants and membrane-foulants. Long-term PET-MPs exposure significantly shifted the microbial community structures. In particular, the abundances of foam-forming filamentous bacteria and quorum-sensing (QS) bacteria, such as Thiothrix, Kouleothrix and Aeromonas, were constantly increasing with the increasing PET-MPs concentration. Furthermore, PET-MPs exposure significantly up-regulated the abundances of genes encoding QS signaling molecules and exopolysaccharides, such as lasI, lsrA and algZ. Collectively, these findings suggested that PET-MPs exposure stimulated the excessive growth of fouling-causing bacteria, which contained more biofilm formation related genes, that consequently accelerated membrane fouling.

Aggregation and construction mechanisms of microbial extracellular polymeric substances with the presence of different multivalent cations: Molecular dynamic simulation and experimental verification

Interactions between cations and extracellular polymeric substances (EPS) play an important role in the formation of microbial aggregates and have key effects on the physical properties of activated sludge across wastewater and sludge treatment process. Here, a molecular model of EPS cluster in activated sludge was constructed and simulated by molecular dynamics (MD) to probe the structural properties of EPS and the interaction between EPS and prevalent multivalent cations (Ca2+, Mg2+, Al3+). Then the predicted changes in physical properties were validated against the dynamic light scattering, XAD resin fractionation and rheology test. The binding dynamics and interactions mechanisms between multivalent cations and EPS functional groups were further investigated using MD in combination with spectroscopic analysis. Results suggest that biopolymers are originally aggregated by electrostatic and intermolecular interactions forming dynamic clusters with negatively charged surface functional groups, which induced electrostatic repulsion preventing further agglomeration of biopolymer clusters. In the presence of multivalent cations, surface polar functional groups in biopolymers are connected, causing the rearrangement of EPS molecular conformation that forms larger and denser agglomerates. Reduced solvent accessible surface area, enhanced hydrophobicity, and increased binding free energy lead to a strong gel-like network of EPS. Ca2+ and Al3+ predominantly interact with functional groups in polysaccharides, promoting agglomeration of macromolecules. In contrast, Mg2+ and Al3+ disrupted the secondary structure of proteins, exposing hydrophobic interaction sites. Al3+ can better agglomerate biopolymers with its higher positive charge and shorter coordination distance as compared to Ca2+ and Mg2+, but compromised by the effect of hydration. This work offers a novel approach to explore the construction and molecular aggregation of EPS, enriching the theoretical basis for optimization of wastewater and sludge treatment.

Exposure to Cr(VI) affects partial denitrification process-nitrite accumulation, EPS characteristic and microbial community assembly

This study was aimed at assessing the effects of elevated Cr(VI) stresses on partial denitrification (PD) process. The results showed that 0.5–5 mg/L Cr(VI) exposure significantly decreased nitrite accumulation rate, while COD removal efficiencies increased due to the further conversion of NO2--N to N2. This suggested that Cr(VI) exposure shifted the biological process from partial denitrification to complete denitrification. The Cr(VI) removal efficiency decreased from 37.75 ± 15.97% to 10.48 ± 3.78% with increasing Cr(VI) concentration. Excitation-emission matrix fluorescence spectroscopy showed that Cr(VI) exposure significantly stimulated the synthesis of tryptophan protein-like, aromatic protein-like and humic acid-like substances in extracellular polymeric substances (EPS). In addition, significant changes in functional groups of EPS were found as revealed by Fourier transform infrared spectroscopy. Particularly, there was a considerable decrease in the α-Helix from 31.36% to 0% and a major increase in the antiparallel β-Sheet from 4.81% to 9.03% with increasing Cr(VI) stresses. The biodiversity decreased significantly under Cr(VI) stresses, and the microbial community structures gradually shifted with increasing Cr(VI) dosage. Sloan model revealed that the relative importance of deterministic processes on the community assembly increased after Cr(VI) exposure, indicating that Cr(VI)-induced selective processes have a profound influence on microbial community of PD process. Network analysis revealed that Cr(VI) exposure significantly altered species-species associations, topological features of individual OTU, and keystone species, implying that substantial changes occurred in bacterial ecology after exposure to Cr(VI).

Exploring the role of extracellular polymeric substances in the antimony leaching of tailings by Acidithiobacillus ferrooxidans.

The concentration of Sb bearing tailings in water located in abandoned antimony mines was found to be a big problem, as they contaminate other water resources and entire food chain. Microorganisms were found to be key in tailing leaching and reaction speeding in the presence of extracellular polymeric substances (EPS) produced by bacteria. Herein, we investigated the pattern of the Sb leaching from Sb bearing tailings using Acidithiobacillus ferrooxidans, and analyzed the mechanism of EPS in the leaching process of Sb. To completely and deeply understand the functions of EPS in the bioleaching of antimony tailings, the generation behavior of EPS produced by Acidithiobacillus ferrooxidans (A. ferrooxidans) during bioleaching was characterized by three-dimensional excitation-emission matrix (3D-EEM). Meanwhile, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) were used to show the changes of EPS functional groups before and after leaching. Compared with the functional groups in EPS produced by A. ferrooxidans before leaching, the content of hydroxyl and amino groups that reduce high-valent metals to low-valent metals in EPS decreases after leaching, and the carbonyl content increases, corresponding to the ratio of trivalent antimony increased, indicating that EPS could reduce the risk of pentavalent antimony to trivalent one. At the same time, with biological scanning electron microscopy and energy spectrum scanning, the observation of EPS on the mineral surface showed that Sb was adsorbed in the EPS, and the XPS of Sb was fine. Spectral analysis showed that the Sb adsorbed in EPS contained both Sb(III) and Sb(V). Besides, for revealing the influence of EPS in the leaching process of Sb from tailings, this work provided an in-depth understanding of the mechanism of Sb released from tailings under the action of A. ferrooxidans and further provides a basis for the biogeochemical cycle of Sb.

A novel treatment for amelioration of sludge dewaterability using green starch-grafted flocculant and realized mechanism

To clarify the effect of extracellular polymeric substances (EPS), protein and hydrophilic substances on the dewatering efficiency during starch-grafted flocculant (SBF) conditioning, a green and cost-saving SBF was synthesized. Dewatering performance of sludge, secondary structure of protein, change of hydrophobic substances and removal of bound water were investigated. Results showed that after SBF conditioning, filter cake moisture content and specific resistance to filtration decreased from 75.63 % and 2.31 × 1012 m/kg to 66.76 % and 5.68 × 1011 m/kg, respectively. SBF neutralized the negative charges from the sludge system, promoting the increase of sludge flocs size and EPS decomposition, decreasing the compressibility of sludge and constructing a channel for water release. Moreover, the secondary structures of protein were changed through the interaction between SBF and the oxygen-containing functional groups in EPS, resulting in the reduction of hydrophilic substances and the increase of hydrophobic substances, which increased the hydrophobicity of molecules and thus improved the dewatering capacity of sludge. Meanwhile, the construction of sludge skeleton channels, charge neutralization, hydrophobic association effect were the primary mechanisms of SBF conditioning sludge dewatering. Additionally, SBF has an excellent economy as a sludge conditioner. This paper provided a new ideal for starch-based flocculants for improving the dewatering capacity of sludge treatment.

Reduction mechanisms of V5+ by vanadium-reducing bacteria in aqueous environments: Role of different molecular weight fractionated extracellular polymeric substances

Extracellular polymeric substances (EPS) are high-molecular polymers secreted by microbes and play essential roles in metallic biogeochemical cycling. Previous studies demonstrated the reducing capacity of the functional groups on EPS for metal reduction. However, the roles of different EPS components in vanadium speciation and their responsible reducing substances for vanadium reduction are still unknown. In this study, the EPS of Bacillus sp. PFYN01 was fractionated via ultrafiltration into six components with different kDa (EPS>100, EPS100–50, EPS50–30, EPS30–10, EPS10–3, and EPS<3). Batch reduction experiments of the intact cells, EPS-free cells, the pristine and fractionated EPS with V5+ were conducted and characterized. The results demonstrated that the extracellular reduction of V5+ into V4+ by EPS was the major reduction process. Among the functional groups in EPS, C=O/C-N of amide in protein/polypeptide and CO of carboxyl in fulvic acid-like substances might act as the reductants for V5+, while CO in polysaccharide molecules and PO in phosphodiester played a key role in the adsorption process. The intracellular reduction was via translocating V5+ into the cells and releasing V4+ by the intracellular reductases. The reducing capacity of the fractionated EPS followed a sequence of EPS<3 > EPS10–3 > EPS50–30 > EPS100–50 > EPS30–10 > EPS>100. The small molecules of fulvic acid-like substances and amino acids were responsible for the high reducing capacity of EPS<3. EPS>100 had the lowest reducing capacity due to its macromolecular structure decreasing the exposure of the reactive sites. In addition to reduction, those intermediate EPS components may also have supporting functions, such as connecting protein skeletons and increasing the specific surface area of EPS. Therefore, the diverse effects of the EPS components cannot be neglected in vanadium biogeochemical cycling.

Extracellular Polymeric Substances and Biocorrosion/Biofouling: Recent Advances and Future Perspectives.

Microbial cells secrete extracellular polymeric substances (EPS) to adhere to material surfaces, if they get in contact with solid materials such as metals. After phase equilibrium, microorganisms can adhere firmly to the metal surfaces causing metal dissolution and corrosion. Attachment and adhesion of microorganisms via EPS increase the possibility and the rate of metal corrosion. Many components of EPS are electrochemical and redox active, making them closely related to metal corrosion. Functional groups in EPS have specific adsorption ability, causing them to play a key role in biocorrosion. This review emphasizes EPS properties related to metal corrosion and protection and the underlying microbially influenced corrosion (MIC) mechanisms. Future perspectives regarding a comprehensive study of MIC mechanisms and green methodologies for corrosion protection are provided.

Effects of coexisting Na+, Mg2+ and Fe3+on nitrogen and phosphorus removal and sludge properties using A2O process

Na+, Mg2+ and Fe3+ are generated in industrial production and human life such as petroleum refining, textiles process and seawater flushing. They can affect sludge activity and operation performance after entering sewage treatment plant. The effects of coexisting Na+, Mg2+ and Fe3+ on nitrogen and phosphorus removal and sludge flocculation were investigated and the distribution of alkaline phosphatase in the sludge was analyzed using A2O process. Fourier transform infrared spectroscopy (FTIR) and three-dimension excitation emission matrix (3D-EEM) were used to explore the changes of extracellular polymeric substances (EPS), and Brunauer-Emmett-Teller (BET) and scanning electron microscopy (SEM) were used to analyze the sludge microstructure, respectively. The results showed that when Na+ concentration was 0.5 g/L and mole ratio of Mg2+/Fe3+ was 3, removal efficiencies of COD, TN and TP were the highest (95%, 89% and 90%), and flocculation ability (FA) was the optimum (43.28%, 44.64% and 43.18%) in anaerobic zone, anoxic zone and oxic zone, respectively. Distribution rule of alkaline phosphatase was Pellet > tightly bound extracellular polymeric substances (TB-EPS) > loosely bound extracellular polymeric substances (LB-EPS) > supernatant. Coexisting Na+, Fe3+ and low concentration of Mg2+ (0.54 mmol/L) increased alkaline phosphatase activity and sludge surface roughness and reduced specific surface area of sludge. Furthermore, these coexisting ions increased EPS concentration, but did not change main compositions and functional groups of EPS.

The presence of low fouling-causing bacteria can lead to decreased membrane fouling potentials of mixed cultures

Presence of low fouling-causing bacteria (FCB) in a dual-species culture remarkably reduced membrane fouling potential of high FCB via interspecies interactions. The Fourier transform infrared analyses reveal that low FCB can modulate the extracellular polymeric substances functional groups of high/low FCB mixed cultures, which in turn alleviate membrane fouling. This suggests that isolation and application of low FCB in membrane bioreactors can be a promising method for membrane fouling control via specific cell-to-cell interactions.

Contrasting detoxification mechanisms of Chlamydomonas reinhardtii under Cd and Pb stress

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

Multiple roles of Ca2+ in the interaction of ciprofloxacin with activated sludge: Spectroscopic investigations of extracellular polymeric substances

Calcium ion is an important cation influencing the binding of recalcitrant organic contaminants with activated sludge during wastewater treatment process, but there is still unknown about its role in amphoteric fluoroquinolones binding. Binding experiments show that Ca2+ markedly inhibited binding of ciprofloxacin (CIP) onto sludge, causing 7–203 times of CIP release. Multi-spectroscopic examinations indicate that tryptophan-like and tyrosine-like proteins in extracellular polymeric substances (EPS) were dominant components for CIP binding by static quenching and forming CIP-proteins complexes. Addition of Ca2+ into EPS and CIP binding systems induced increase of association constants (from 0.024–0.064 to 0.027–0.084 L/μmol) and binding constants (from 0.002–0.039 to 0.012–0.107) and decrease of binding sites number (from 0.893–2.007 to 0.721–1.386). Functional groups of EPS and secondary structure of proteins were remarkably changed upon reactions with CIP and Ca2+. Calcium ion interacted with EPS and CIP binding system in two distinct ways: Ca2+ shielded CO in amide I in EPS for CIP binding, whereas strengthened binding between CIP and functional groups including CO in carboxyl groups in extra-microcolony polymers and OH in extra-cellular polymers by forming ternary complexes. Cation competition for CO in amide I is responsible for Ca2+ induced CIP release from the sludge. Results suggest the highly potential release of CIP from high saline wastewater and cation-conditioned sludge which needs further monitoring and evaluation.

Extracellular polymeric substances alter cell surface properties, toxicity, and accumulation of arsenic in Synechocystis PCC6803

Arsenic (As) contamination of water poses severe threats to human health and thus requires effective remediation methods. In this study, Synechocystis PCC6803, a model cyanobacterium common in aquatic environments, was used to investigate the role of extracellular polymeric substances (EPS) in As toxicity, accumulation, and transformation processes. We monitored the growth of Synechocystis with As exposure, measured the zeta potential and binding sites on the cell surface, and analysed As accumulation and speciation in Synechocystis cells with and without EPS. After EPS removal, the binding sites and zeta potential of the cell surface decreased by 44.43% and 31.9%, respectively. The growth of Synechocystis decreased 49.4% and 43.7% with As(III) and As(V) exposure, and As accumulation in the cells decreased by 12.8–44.5% and 14–42.7%, respectively. As absorption was enhanced in cells with EPS removed. The oxidation of As(III) and reduction of As(V) were significantly greater in cells with intact EPS compared to those with EPS removed. Fourier transform infrared spectroscopy (FTIR) showed that functional groups of EPS and Synechocystis cells, including –NH, –OH, CO, and CC, interacted with As species. Together the results of this work demonstrate that EPS have significant impacts on cell surface properties, thereby affecting As accumulation and transformation in Synechocystis PCC6803. This work provides a basis for using EPS to remedy As pollution in aquatic environments.

Effect of extracellular polymeric substances on arsenic accumulation in Chlorella pyrenoidosa

Inorganic arsenic (iAs) in its dominant dissolved phase in the environment is known to pose major threats to ecological and human health. While the biological effects in many arsenic-bearing freshwaters have been extensively studied, the behavior and bioaccumulation of dissolved iAS in the presence of extracellular polymeric substances (EPS) still remains to be a critical knowledge gap. In this study, the uptakes and kinetic characteristics of iAs were studied using Chlorella pyrenoidosa (a typical freshwater green algae) by addressing the different effects of EPS on arsenite (AsШ) and arsenate (AsV). The arsenic uptake capacity increased as the exposure concentration increased from 0 to 300 µmol L−1, and the uptake rate constants (Ku) in the Bio-dynamic model were greater for AsV than AsШ (0.63–11.57 L g−1 h−1 vs. 0.44–5.43 L g−1 h−1). The toxic effects as mitigated by EPS were observed through the morphological changes of algal cells by TEM and SEM. When compared with the EPS-free algal cells (EPS-F), EPS-covered cells (EPS-C) had a higher arsenic adsorption capacity through EPS-enhanced surface adsorption and reduced intracellular uptake. The overall decrease (35% and 23.3% for AsШ and AsV, respectively) in the maximum uptake capacity in intact algae cells favors cell’s tolerance to the toxic effects of iAs. These observed discrepancies between AsШ and AsV and between EPS-C and EPS-F were further elucidated through morphological images (TEM and SEM) and molecular/atomic spectroscopic data that combine three-dimensional excitation-emission matrix fluorescence spectroscopy (3D-EEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Altogether, the spectroscopic evidence revealed the interactions of iAs with C–O–C, C–O–H and –NH2 functional groups in EPS’ tyrosine- and tryptophan-like proteins as the binding sites. Overall, this study for the first time provides comprehensive evidence on the iAs-EPS interactions. Such insights will benefit our understanding of the biogeochemical processes of iAs and the strategic development of bioremediation techniques involving microalgae in the natural and engineered systems.

Extracellular Polymeric Substances of ANAMMOX Granular Sludge and Its Effects on Sludge Surface Characteristics

The anaerobic ammonium oxidation(ANAMMOX) granular sludge in the EGSB reactor was divided into three groups according to particle size, which were R1 (0.5-1.4 mm), R2 (1.4-2.8 mm), and R3 (>2.8 mm). Extracellular polymeric substances (EPS) of different sizes from ANAMMOX granular sludge were extracted, and the EPS characteristics and their influence on the surface characteristics of ANAMMOX aggregates were analyzed. With the increased particle size of ANAMMOX granular sludge, the PS content was between (10.69±0.11)-(12.28±0.15) mg·g-1, while the PN content increased from (56.88±0.86) mg·g-1 to (98.59±2.10) mg·g-1, and PN/PS increased from 5.32 to 9.05. The EPS functional groups and the content of three-dimensional fluorescent components of different size ANAMMOX granular sludge were different. As the granular sludge size increased, the value of α-helix/(β-sheet + random coil) gradually decreased from 0.60 to 0.43, which is beneficial to the hydrophobicity expression of the sludge. Due to the increased particle size of the granular sludge, the hydrophobicity of the sludge surface increased from 54.2% to 63.1%, and the Zeta potential increased from -41.2 mV to -31.5 mV. The increased hydrophobicity and surface charge are beneficial to the formation of sludge aggregates. EPS can enhance ANAMMOX sludge hydrophobicity and increase Zeta potential. The presence of PN in EPS is essential to this process.

Functional Determinants of Extracellular Polymeric Substances in Membrane Biofouling: Experimental Evidence from Pure-Cultured Sludge Bacteria.

The aim of this work was to better understand the roles of extracellular polymeric substances (EPS) in membrane biofouling at the single-strain level. In the present study, a total of 23 bacterial strains were isolated from a sludge sample. The EPS extracted from pure-cultured bacteria were assessed for their fouling potentials and were simultaneously analyzed using Fourier transform infrared spectroscopy (FTIR). Further, the impact of calcium on the chemical composition of EPS and membrane fouling behavior was investigated in a strain-dependent manner. The EPS of the 23 bacterial strains exhibited different IR features for protein and polysaccharide regions. In addition, an α-1,4-glycosidic linkage (920 cm-1) and amide II (1,550 cm-1) correlated very well with the fouling potentials of all pure-cultured bacteria. In contrast to low-fouling strains, medium- and high-fouling strains exhibited two distinct peaks at 1,020 cm-1 (uronic acids) and 1,250 cm-1 (O-acetyl), which accelerate membrane fouling given their gelling capacities. In the presence of calcium, the fouling potential of a high-fouling strain (Bacillus sp. strain JSB10) was profoundly reduced (P < 0.0005) due to the binding activity of an α-1,4-glycosidic linkage and amide II with calcium. However, the impact of calcium on a low-fouling strain (Vagococcus sp. strain JSB21) was insignificant. Two-dimensional FTIR correlation spectroscopic (2D-FTIR-COS) analysis further revealed that the susceptibilities of functional groups to calcium largely relied on the composition and abundance of the above-described functional groups in EPS. These findings suggest that bacterial strains with different fouling potentials exhibit varied responses to calcium.IMPORTANCE Membrane biofouling is one of the main challenges for the operation of membrane-based processes used for water and wastewater treatment. This study revealed the functional determinants of EPS in membrane biofouling of 23 bacterial strains isolated from a full-scale membrane bioreactor (MBR) plant. We found that an α-1,4-glycosidic bond, amide II, and uronic acids of EPS significantly correlated with the fouling potentials of bacteria. The roles of these EPS groups in membrane fouling were impacted by calcium resulting from EPS-calcium interactions. In addition, our results also demonstrated that any perturbations in the sludge bacterial community in MBRs can lead to varied filtration potentials of the bulk liquor.

Aggregation ability of three phylogenetically distant anammox bacterial species

Anaerobic ammonium-oxidizing (anammox) bacteria are well known for their aggregation ability. However, very little is known about cell surface physicochemical properties of anammox bacteria and thus their aggregation abilities have not been quantitatively evaluated yet. Here, we investigated the aggregation abilities of three different anammox bacterial species: “Candidatus Brocadia sinica”, “Ca. Jettenia caeni” and “Ca. Brocadia sapporoensis”. Planktonic free-living enrichment cultures of these three anammox species were harvested from the membrane bioreactors (MBRs). The physicochemical properties (e.g., contact angle, zeta potential, and surface thermodynamics) were analyzed for these anammox bacterial species and used in the extended DLVO theory to understand the force-distance relationship. In addition, their extracellular polymeric substances (EPSs) were characterized by X-ray photoelectron spectroscopy and nuclear magnetic resonance. The results revealed that the “Ca. B. sinica” cells have the most hydrophobic surface and less hydrophilic functional groups in EPS than other anammox strains, suggesting better aggregation capability. Furthermore, aggregate formation and anammox bacterial populations were monitored when planktonic free-living cells were cultured in up-flow column reactors under the same conditions. Rapid development of microbial aggregates was observed with the anammox bacterial population shifts to a dominance of “Ca. B. sinica” in all three reactors. The dominance of “Ca. B. sinica” could be explained by its better aggregation ability and the superior growth kinetic properties (higher growth rate and affinity to nitrite). The superior aggregation ability of “Ca. B. sinica” indicates significant advantages (efficient and rapid start-up of anammox reactors due to better biomass retention as granules and consequently stable performance) in wastewater treatment application.

Investigation of composition, structure and bioactivity of extracellular polymeric substances from original and stress-induced strains of Thraustochytrium striatum

This paper was the first to study extracellular polymeric substances (EPSs) of Thraustochytrium striatum on composition, structure and bioactivities. Two strains of T. striatum including original (ori) and high-biomass (mut) strains (induced by high-nitrogen stress) were compared. The EPSs from both strains mainly contained polysaccharide (41–64%, w/w, dry basis) and protein (25–40%, w/w, dry basis), which was shown by the morphology study with an AFM. The monosaccharide profile of the EPS polysaccharide was consisted of glucose, galactose, arabinose, and trace amount of xylose. Glucose and arabinose took up to 82–90% (w/w, dry basis) of the total polysaccharide. The structure and functional groups of EPSs were determined by FTIR and NMR. The NMR results revealed that the major structural linkages of the polysaccharides of both ori and mut EPSs were 1 → 6-β-glucan and 1 → 4-α-galactan branched with l-α-arabinose. The EPSs were found to have anti-tumor activities against mouse melanoma B16-F0, human prostate carcinoma DU145, human cervical carcinoma HeLa, and human lung carcinoma A549. The EPSs also showed antioxidant and anti-inflammatory activities and antibacterial activity against Pseudomonas aeruginosa.

Composition and functional group characterization of extracellular polymeric substances (EPS) in activated sludge: the impacts of polymerization degree of proteinaceous substrates

Characteristics of extracellular polymeric substances (EPS) in activated sludge strongly depend on wastewater substrates. Proteinaceous substrates (ProS) present in heterogeneous polymeric form are intrinsic and important parts of wastewater substrates for microorganisms in activated sludge systems. However, correlations between ProS and characteristics of EPS are scarce. This study systematically explored the impacts of monomeric (Mono-), low polymeric (LoP-) and high polymeric (HiP-) ProS on compositions and functional groups of EPS in activated sludge. The results showed that the change of polymerization degree of ProS significantly altered the composition of EPS. Compared to EPSMono-ProS, the proportion of proteins in EPSLoP-ProS and EPSHiP-ProS increased by 12.8% and 27.7%, respectively, while that of polysaccharides decreased by 22.9% and 63.6%, respectively. Moreover, the proportion of humic compounds in EPSLoP-ProS and EPSHiP-ProS were ∼6 and ∼16–fold higher than that in EPSMono-ProS, respectively. The accumulation of humic compounds in EPS increased the unsaturation degree of EPS molecules, and thereby reduced the energy requirement for electrons transition of amide bonds and aromatic groups. Size exclusion chromatography (SEC) analyses detected more molecular clusters in EPSHiP-ProS, indicating more complex composition of EPS in HiP-ProS fed activated sludge. Spectroscopic characterization revealed the dominance of hydrocarbon, protein, polysaccharide and aromatic associated bonds in all three EPS. Nevertheless, with the increase of polymerization degree of ProS, the protein associated bonds (such as CONH, CO, NC, NH) increased, while the polysaccharide associated bonds (such as COC, COH, OCOH) decreased. This paper paves a path to understand the role of ProS in affecting the production and characteristics of EPS in biological wastewater treatment systems.

Effects of hexavalent chromium on performance, extracellular polymeric substances and microbial community structure of anaerobic activated sludge in a sequencing batch reactor

AbstractBACKGROUNDBioremediation of Cr(VI) to Cr(III) was considered a promising and cost‐effective alternative to chemical and physical methods. However, Cr(VI) had toxic effects on microorganisms. This study focused on exploring the effects of different Cr(VI) concentrations on the performance of an anaerobic activated sludge reactor, extracellular polymeric substances (EPS) and microbial community structure.RESULTSAnaerobic sludge reduced and immobilized 100.0 mg L−1 Cr(VI) in 24 h. When the Cr(VI) concentration was increased from 0.0 to 50.0 mg L−1, the production of EPS was enhanced from 231.4 to 1262.9 mg g−1 VSS. With 80.0 mg L−1 Cr(VI) and 120.0 mg L−1 Cr(VI), EPS production was inhibited. Increase of Cr(VI) concentration changed the EPS components and had distinct effects on the functional groups of EPS. In addition, the increase of Cr(VI) stress reduced the abundance of most bacteria.CONCLUSIONLow Cr(VI) concentrations had no effect on CODCr and NO3‐N removal, while 120.0 mg L−1 Cr(VI) seriously inhibited on CODCr, NO3‐N and Cr(VI) removal. This was due to the toxicity and electron competition ability of Cr(VI). High Cr(VI) concentrations (80.0 and 120.0 mg L−1) also inhibited EPS production. Cr(VI) reduction was closely related with EPS. © 2017 Society of Chemical Industry