Microbial Extracellular Polymeric Substances Research Articles

The effect of extracellular polymeric substances on MICP solidifying rare earth slags and stabilizing Th and U.

Microbially induced carbonate precipitation (MICP) has been used to cure rare earth slags (RES) containing radionuclides (e.g. Th and U) and heavy metals with favorable results. However, the role of microbial extracellular polymeric substances (EPS) in MICP curing RES remains unclear. In this study, the EPS of Lysinibacillus sphaericus K-1 was extracted for the experiments of adsorption, inducing calcium carbonate (CaCO3) precipitation and curing of RES. The role of EPS in in MICP curing RES and stabilizing radionuclides and heavy metals was analyzed by evaluating the concentration and morphological distribution of radionuclides and heavy metals, and the compressive strength of the cured body. The results indicate that the adsorption efficiencies of EPS for Th (IV), U (VI), Cu2+, Pb2+, Zn2+, and Cd2+ were 44.83%, 45.83%, 53.7%, 61.3%, 42.1%, and 77.85%, respectively. The addition of EPS solution resulted in the formation of nanoscale spherical particles on the microorganism surface, which could act as an accumulating skeleton to facilitate the formation of CaCO3. After adding 20 mL of EPS solution during the curing process (Treat group), the maximum unconfined compressive strength (UCS) of the cured body reached 1.922 MPa, which was 12.13% higher than the CK group. The contents of exchangeable Th (IV) and U (VI) in the cured bodies of the Treat group decreased by 3.35% and 4.93%, respectively, compared with the CK group. Therefore, EPS enhances the effect of MICP curing RES and reduces the potential environmental problems that may be caused by radionuclides and heavy metals during the long-term sequestration of RES.

Biogeochemical traces and microbe-mineral interactions in the hyperarid core of the Atacama Desert

Life found various ways to thrive in hostile desert environments. Common adaptation mechanisms are protection against desiccation and UV radiation in biofilms and biocrusts as well as the hypolithic and endolithic colonization of rocks. One of those hostile regions is the Atacama Desert in Northern Chile with its hyperarid core, counted among the most arid places on Earth. Besides the aridity, life faces severe restrictions in these surroundings, e.g. extremely high UV radiation, scarce nutrient supply, and immense salt concentrations. Still, microbial communities and soil organic matter are crucial for the stability of soils and surface sediments in arid ecosystems. Combining molecular mass spectrometry for lipid biomarkers, scanning electron microscopy, and nuclear magnetic resonance spectroscopy, we individually investigated two factors that are of particular importance for the stability of dryland landscapes now and in the future: 1) We studied biogeochemical traces (organic remnants) in surface sediments along an aridity gradient with regard to possible decomposition and/or sequestration of organic compounds. 2) We investigated the interaction of lithobiontic and endolithic microbial communities with the mineral surface with special regard to the stability of soil and surface sediment structures in different areas of the Atacama Desert: in the region of the Salar Grande, Pisagua, and the Quebrada da Aroma. We analyzed halite- and calcium sulfate-dominated evaporitic crusts with and without visible microbial colonization. Organic traces were present in all investigated samples. Following an aridity gradient along the Quebrada de Aroma from an annual precipitation of about 20 mm to the hyperarid core with approx. 2 mm, we found a decrease in functionalized molecular compounds and plant-derived biomarkers (long-chain fatty acids, sterols) as well as an increase in aromatic hydrocarbons, indicating strongly decomposed remnants of plants and microorganisms. The investigation of halite- and calcium sulfate-dominated evaporitic crusts from the Salar Grande, Pisagua, and Aroma region revealed tight interactions of microorganisms with the mineral substrate. Indications of recent bacterial activity were ubiquitous (e.g. short-chain membrane fatty acids, carbohydrates of extracellular polymeric substances (EPS)). Scanning electron microscopy revealed that especially the microbial EPS within evaporites seems to biochemically stabilize mineral aggregates by agglutination. Moreover, fungal biomarkers showed that fungi and fungal parts of lichen were not only present at the surface of physical soil crusts but form widespread networks in the crusts and thereby contribute significantly to the physical stabilization of soils and surface sediments and erosion protection.

Microbial community and extracellular polymeric substance dynamics in arid–zone temporary pan ecosystems

Microbial extracellular polymeric substances (EPS) are an important component in sediment ecology. However, most research is highly skewed towards the northern hemisphere and in more permanent systems. This paper investigates EPS (i.e., carbohydrates and proteins) dynamics in arid Austral zone temporary pans sediments. Colorimetric methods and sequence–based metagenomics techniques were employed in a series of small temporary pan ecosystems characterised by alternating wet and dry hydroperiods. Microbial community patterns of distribution were evaluated between seasons (hot–wet and cool–dry) and across depths (and inferred inundation period) based on estimated elevation. Carbohydrates generally occurred in relatively higher proportions than proteins; the carbohydrate:protein ratio was 2.8:1 and 1.6:1 for the dry and wet season respectively, suggesting that EPS found in these systems was largely diatom produced. The wet– hydroperiods (Carbohydrate mean 102 μg g−1; Protein mean 65 μg g−1) supported more EPS production as compared to the dry– hydroperiods (Carbohydrate mean 73 μg g−1; Protein mean 26 μg g−1). A total of 15,042 Unique Amplicon Sequence Variants (ASVs) were allocated to 51 bacterial phyla and 1127 genera. The most abundant genera had commonality in high temperature tolerance, with Firmicutes, Actinobacteria and Proteobacteria in high abundances. Microbial communities were more distinct between seasons compared to within seasons which further suggested that the observed metagenome functions could be seasonally driven. This study's findings implied that there were high levels of denitrification by mostly nitric oxide reductase and nitrite reductase enzymes. EPS production was high in the hot–wet season as compared to relatively lower rates of nitrification in the cool–dry season by ammonia monooxygenases. Both EPS quantities and metagenome functions were highly associated with availability of water, with high rates being mainly associated with wet– hydroperiods compared to dry– hydroperiods. These data suggest that extended dry periods threaten microbially mediated processes in temporary wetlands, with implications to loss of biodiversity by desiccation.

Bioremediation of heavy metals-contaminated sites by microbial extracellular polymeric substances – A critical view

Heavy metal contamination in the atmosphere poses substantial threats to ecosystems. Traditional methods for the removal of HM-contaminated sites, such as physical and chemical treatments, often have limitations in terms of efficiency, cost, and potential negative impacts on the environment. As a result, there is growing interest in exploring alternative and sustainable approaches, such as bioremediation. Bioremediation is a promising technology that utilizes the inherent abilities of microorganisms to degrade or transform pollutants into less harmful forms. Microbial exopolysaccharides have gained attention as potential tools in bioremediation strategies due to their unique physicochemical properties and their ability to interact with heavy metals. This work aims to provide an overview of the role of microbial extracellular polymeric substances (EPS) in the bioremediation of HM-contaminated sites. First, the mechanisms by which EPS facilitates heavy metal sequestration are discussed. EPS can form metal-complexing agents, such as chelators and ion-binding sites, which enhance the immobilization and precipitation of heavy metals, reducing their bioavailability and toxicity. EPS can act as a protective barrier, shielding microorganisms from heavy metal stress and facilitating their survival and growth. Additionally, EPS production can be induced or enhanced in response to heavy metal exposure, potentially increasing the efficiency of bioremediation processes.

Electro living membrane bioreactor for highly efficient wastewater treatment and fouling mitigation: Influence of current density on process performances

The next generation of the self-forming dynamic membrane, referred to in this study as the “Living Membrane (LM)”, is a new patented technology based on an encapsulated biological layer that self-forms on a designed coarse-pore size support material during wastewater treatment and acts as a natural membrane filter. Integrating electrochemical processes with wastewater treatment using the LM approach has also been recently studied (the reactor is referred to as the Electro-Living Membrane Bioreactor or e-LMBR). This study investigated the effects of varying current densities, i.e., 0.3, 0.5, and 0.9 mA/cm2, on the performance of an e-LMBR. The results were also compared with those of the Living Membrane Bioreactor or LMBR (without applied current density).Higher pollutant removals were observed in the presence of the electric field. However, the effect of varying applied current densities on the COD (98–99 %), NH3-N (97–99 %), and PO43−P (100 %) removals was not statistically significant. The more prominent differences (p < 0.05) were observed in the decrease of NO3−-N concentrations from mixed liquor to effluent, with increasing current density resulting in lower mean NO3−-N effluent concentrations (0.3 mA/cm2: 6.13 mg/L; 0.5 mA/cm2: 4.38 mg/L; 0.9 mA/cm2: 3.70 mg/L). The reduction of NO3−-N concentrations as wastewater permeated through the LM layer also confirmed its role in removing nitrogen-containing compounds.Higher current densities resulted in lower concentrations of fouling substances, particularly those of microbial extracellular polymeric substances (EPS) and transparent exopolymer particles (TEPs). The average values of the temporal variation of transmembrane pressure (d(TMP)/d(t)) in the e-LMBR were extremely low, in the range of 0.013–0.041 kPa/day, throughout the operation period. The highest (d(TMP)/d(t)) was observed for the highest current density. However, the TMP values remained below 2 kPa in all the e-LMBR runs even after the initial LM formation stage.

Optimizing carbon sources regulation in the biochemical treatment systems for coal chemical wastewater: Aromatic compounds biodegradation and microbial response strategies

The complex composition of coal chemical wastewater (CCW), marked by numerous highly toxic aromatic compounds, induces the destabilization of the biochemical treatment system, leading to suboptimal treatment efficacy. In this study, a biochemical treatment system was established to efficiently degrade aromatic compounds by quantitatively regulating the dosage of co-metabolized substrates (specifically, the chemical oxygen demand (COD) Glucose: COD Sodium acetate = 3:1, 1:3, and 1:1). The findings demonstrated that the system achieved optimal performance under the condition that the ratio of COD Glucose to COD Sodium acetate was 3:1. When the co-metabolized substrate was added to the system at an optimal ratio, examination of pollutant removal and cumulative effects revealed that the removal efficiencies for COD and total organic carbon (TOC) reached 94.61 % and 86.40 %, respectively. The removal rates of benzene series, nitrogen heterocyclic compounds, polycyclic aromatic hydrocarbons, and phenols were 100 %, 100 %, 63.58 %, and 94.12 %, respectively. Research on the physiological response of microbial cells showed that, under optimal ratio regulation, co-metabolic substrates led to a substantial rise in microbial extracellular polymeric substances (EPS) secretion, particularly extracellular proteins. When the system reached the end of its operation, the contents of loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) for proteins in the optimal group were 7.12 mg/g-SS and 152.28 mg/g-SS, respectively. Meanwhile, the ratio of α-Helix / (β-Sheet + Random coil) and the proportion of intermolecular interaction forces were also increased in the optimal group. At system completion, the ratio of α-Helix / (β-Sheet + Random coil) reached 0.717 (LB-EPS) and 0.618 (TB-EPS), respectively. Additionally, the proportion of intermolecular interaction forces reached 74.83 % (LB-EPS) and 55.03 % (TB-EPS). An in-depth analysis of the metabolic regulation of microorganisms indicated that the introduction of optimal ratios of co-metabolic substrates contributed to a noteworthy upregulation in the expression of Catechol 2,3-dioxygenase (C23O) and Dehydrogenase (DHA). The expression levels of C23O and DHA were measured at 0.029 U/mg Pro·g MLSS and 75.25 mg TF·(g MLSS·h)−1 (peak value), respectively. Correspondingly, enrichment of aromatic compound-degrading bacteria, including Thauera, Saccharimonadales, and Candidatus_Competibacter, occurred, along with the upregulation of associated functional genes such as Catechol 1,2-dioxygenase, Catechol 2,3-dioxygenase, Protocatechuate 3,4-dioxygenase, and Protocatechuate 4,5-dioxygenase. Considering the intricate system of multiple coexisting aromatic compounds in real CCW, this study not only obtained an optimal ratio for carbon source addition but also enhanced the efficient utilization of carbon sources and improved the capability of the system to effectively degrade aromatic compounds. Additionally, this paper established a theoretical foundation for metabolic regulation and harmless treatment within the biochemical treatment of intricate systems, exemplified by real CCW.

Effects and mechanisms of oxytetracycline and norfloxacin on microbial extracellular polymeric substances (EPS) in biological denitrification of aquaculture wastewater

The direct equalizing ray method was employed to design three groups of mixtures of oxytetracycline(OTC) and norfloxacin(NOR) with varying proportions(Group R1 had a higher proportion of OTC, while R2 had similar concentrations of both antibiotics, and R3 had a higher proportion of NOR).The effects of these mixtures on the content and properties of extracellular polymeric substances (EPS) in the biological denitrification process were investigated using an sequencing batch reactor activated sludge reactor (SBR). The results revealed that the removal rates of ammonia nitrogen(NH3-N) decreased in all three groups with the addition of antibiotics. As the antibiotic concentration increased, the EPS content decreased by 68.46%, 55.53%, and 65.03% in R1, R2, and R3, respectively. To understand the interaction mechanism of mixed antibiotics on EPS in activated sludge, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) techniques were employed. The findings demonstrated significant effects of mixed antibiotics on functional groups such as C-O, CO, and C-O-C. Specifically, hydrogen bonding was found to be the primary influencing factor in the R1 ratio, while Π-Π conjugation played a major role in the R3 ratio.

Lead removal from the aqueous solution by extracellular polymeric substances produced by the marine diatom Navicula salinicola

ABSTRACT Microbial extracellular polymeric substances (EPS) have recently emerged as significant contributors in diverse biotechnological applications. Extracellular polymeric substances (EPS), produced by a Navicula salinicola strain, have been studied for potential applications in a specific heavy metal (lead (Pb II)) removal from wastewater. The optimisation of operational parameters, mainly pH, Pb and EPS concentrations, using the Box–Behnken design (BBD) was undertaken to enhance lead uptake. The higher Pb adsorption capacity reached 2211.029 mg/g. Hydroxyl, carbonyl, carboxyl, phosphoric, and sulfhydryl groups were identified quantitatively as potential sites for Pb adsorption. EPS exhibited a notable flocculation rate of 70.20% in kaolin clay at a concentration of 15 mg/L. They demonstrated an emulsifying activity greater than 88%, showcasing their versatile potential for both sedimentation processes and stabilising liquid–liquid systems. EPS could be excellent nonconventional renewable biopolymers for treating water and wastewater.

Biological soil crust elicits microbial community and extracellular polymeric substances restructuring to reduce the soil erosion on tropical island, South China Sea

Soil erosion stands as the preeminent environmental concern globally, attaining heightened significance, particularly within islands where land resources prove notably scarce. Biological soil crusts, referred to as biocrusts, assume a pivotal ecological role in soil conservation. Notably, they augment the horizontal stability of the substrate through the exudation of microbial extracellular polymeric substances (EPS), thereby shielding the soil against shear stress, exemplified in the form of water erosion. While extant research has delved into the anti-erosion mechanisms of biocrusts in arid landscapes, a conspicuous lacuna persists in the exploration of coral island environments. In this study, we collected and assessed 30 samples encompassing dark biocrusts, light biocrusts, and bare soil to scrutinize the potential anti-erosion efficacy of tropical coral island biocrusts within the South China Sea. Employing a cohesive strength meter, we quantified soil shear stress across various stages of biocrust development, revealing a discernible enhancement in soil erosion resistance during the formation of biocrusts. Relative to the exposed bare soil, the soil shear stress exhibited an escalation from 0.33 N m−2 to 0.61 N m−2 and 1.31 N m−2 in the light biocrusts and dark biocrusts, respectively. Mechanistically, we assayed microbial EPS contents, exposing a positive correlation between EPS and soil anti-erodibility, encompassing extracellular protein and polysaccharide. Concurrently, bacterial abundance displayed a significant augmentation commensurate with biocrust formation and development. In pursuit of elucidating the origin of EPS, high-throughput amplicon sequencing was executed to identify microorganisms contributing to biocrust development. Correlation analysis discerned Cyanobacteria, Chloroflexi, Deinococcota, and Patescibacteria as potential microbials fostering EPS production and fortifying erosion resistance. Collectively, our study presents the first evidence that biocrust from tropical coral reef island in the South China Sea promotes resistance to soil erosion, pinpointing key EPS-producing microbials against soil erosion. The findings would provide insights for island environment restoration.

Harnessing the potential of ginkgo biloba extract: Boosting denitrification performance through accelerated electron transfer

Ginkgo biloba extract (GBE) had several effects on the human body as one of the widely used phytopharmaceuticals, but it had no application in microbial enhancement in the environmental field. The study focused on the impact of GBE on denitrification specifically under neutral conditions. At the identified optimal addition ratio of 2% (v/v), the system exhibited a noteworthy increase in nitrate reduction rate (NRR) by 56.34%, elevating from 0.71 to 1.11 mg-N/(L·h). Moreover, the extraction of microbial extracellular polymeric substance (EPS) at this ratio revealed changes in the composition of EPS, the electron exchange capacity (EEC) was enhanced from 87.16 to 140.4 μmol/(g C), and the transfer impedance was reduced within the EPS. The flavin, fulvic acid (FA), and humic acid (HA) provided a π-electron conjugated structure for the denitrification system, enhancing extracellular electron transfer (EET) by stimulating carbon source metabolism. GBE also improved electron transfer system activity (ETSA) from 0.025 to 0.071 μL O2/(g·min·prot) and the content of NADH enhanced by 22.90% while significantly reducing the activation energy (Ea) by 85.6% in the denitrification process. The synergy of improving both intracellular and extracellular electron transfer, along with the reduction of Ea, notably amplified the initiation and reduction rates of the denitrification process. Additionally, GBE demonstrated suitability for denitrification across various pH levels, enhancing microbial resilience in alkaline conditions and promoting survival and proliferation. Overall, these findings open the door to potential applications of GBE as a natural additive in the environmental field to improve the efficiency of denitrification processes, which are essential for nitrogen removal in various environmental contexts.

In-situ characterization of dynamic Acidithiobacillus ferrooxidans-pyrite interaction via QCM-D-based method: Cell adhesion and biofilm formation in responding to surface sulfur speciation

Microbe-sulfide mineral interactions (MSMI), often manifested as biofilm formation, are ubiquitous in natural and engineered environments. Such interactions were much dependent upon the evolution of chemical species of mineral surface and microbial extracellular polymeric substances (EPS), and in-situ characterization of which have been a demanding and crucial task. In this study, quartz crystal microbalance with dissipation (QCM-D) was used to real time characterize the adhesion of Acidithiobacillus ferrooxidans onto the pyrite surface after introducing L-cysteine (an important component of EPS). And by combining with monitoring the EPS composition in biofilm by confocal laser scanning microscopy (CLSM) and the surface sulfur species by SEM-EDS and X-ray-photoelectron spectroscopy (XPS) as well as the changes in pH, ORP, [Fe2+] and [Fe3+] in solution during A. ferrooxidans-pyrite interaction, the results show that L-cysteine can lead to the Cys-S-S2Fe complex formation on pyrite surface, and under the dosage of 0.02 to 0.1 g/L of L-cysteine, the Cys-S-S2Fe complex promoted the cell adhesion and biofilm formation of A. ferrooxidans with secretion of more EPS proteins but less EPS glycoconjugates, resulting in the promotion of sulfur biooxidation with inhibition of iron biooxidation, corresponding to no obvious formation of jarosites. The higher dosage of L-cysteine (e.g., 0.2 g/L) inhibited biofilm formation, reduced iron/sulfur oxidation. These results deepen the understanding of the roles of L-cysteine on MSMI. This study demonstrates the QCM-D-based method can be widely used for in situ characterization of MSMI, and opens an alternative pathway for revealing the micro-mechanism of MSMI correlated to the macroscopic effects.

Formation of extracellular polymeric substances corona on TiO2 nanoparticles: Roles of crystalline phase and exposed facets

Nanoparticles (NPs) in the environment can interact with macromolecules in the surrounding environment to form eco-corona on their surfaces, which in turn affects the environmental fate and toxicity of nanoparticles. Wastewater treatment plants containing large amounts of microbial extracellular polymeric substances (EPS) are an important source of NPs into the environment, where the formation of EPS coronas on NPs is critical. However, it remains unclear how the crystalline phase and exposed facets, which are intrinsic properties of NPs, affect the formation of EPS coronas on NPs. This study investigated the formation of EPS corona on three TiO2 NPs (representing the most widely used engineered NPs) with different crystalline phases and exposed facets. The protein type and abundance in EPS coronas on TiO2 NPs varied depending on the crystalline phase and exposed facets. Anatase with {101} facets and {001} facets preferred to adsorb proteins with lower molecular weights and higher H-bonding relevant amino acids, respectively, while EPS corona on rutile with {110} facets had proteins with higher hydrophobicity. In addition, the selective adsorption of proteins was primarily determined by steric hindrance, hydrogen bonding, and hydrophobic interaction between TiO2 NPs and proteins, which were affected by changes in aggregation state, surface hydroxyl density, and hydrophobicity of TiO2 NPs induced by crystalline phase and exposed facets. Moreover, crystalline phase and exposed facets-induced EPS corona changes altered the aggregation state and oxidation potential of TiO2–EPS corona complexes. These findings emphasize the important role of crystalline phase and exposed facets in the environmental behavior of nanoparticles and may provide insights into the safe design of nanoparticles.

Rise of tissue- and species-specific 3D bioprinting based on decellularized extracellular matrix-derived bioinks and bioresins

Thanks to its natural complexity and functionality, decellularized extracellular matrix (dECM) serves as an excellent foundation for creating highly cell-compatible bioinks and bioresins. This enables the bioprinted cells to thrive in an environment that closely mimics their native ECM composition and offers customizable biomechanical properties. To formulate dECM bioinks and bioresins, one must first pulverize and/or solubilize the dECM into non-crosslinked fragments, which can then be chemically modified as needed. In bioprinting, the solubilized dECM-derived material is typically deposited and/or crosslinked in a layer-by-layer fashion to build 3D hydrogel structures. Since the introduction of the first liver-derived dECM-based bioinks, a wide variety of decellularized tissue have been employed in bioprinting, including kidney, heart, cartilage, and adipose tissue among others. This review aims to summarize the critical steps involved in tissue-derived dECM bioprinting, starting from the decellularization of the ECM to the standardized formulation of bioinks and bioresins, ultimately leading to the reproducible bioprinting of tissue constructs. Notably, this discussion also covers photocrosslinkable dECM bioresins, which are particularly attractive due to their ability to provide precise spatiotemporal control over the gelation in bioprinting. Both in extrusion printing and vat photopolymerization, there is a need for more standardized protocols to fully harness the unique properties of dECM-derived materials. In addition to mammalian tissues, the most recent bioprinting approaches involve the use of microbial extracellular polymeric substances in bioprinting of bacteria. This presents similar challenges as those encountered in mammalian cell printing and represents a fascinating frontier in bioprinting technology.

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.

Effect of free nitrous acid on extracellular polymeric substances production and membrane fouling in a nitritation membrane bioreactor

The membrane bioreactor (MBR) with nitritation based nitrogen removal processes has attracted growing interest in recent years, although membrane fouling in the nitritation MBR is a challenging issue. In this study, the inhibitory effect of free nitrous acid (FNA) on microbial extracellular polymeric substances (EPS) production and membrane fouling in a nitritation MBR was investigated. Results showed that EPS played a critical role in the biofouling process, and EPS production was affected by FNA concentration. As FNA concentration increased from 5.10 × 10−3 mg N/L to 1.34 × 10−2 mg N/L, protein (PN) and polysaccharide (PS) contents increased from 8.20 to 60.28 mg/g VSS and 4.74–30.46 mg/g VSS, respectively. However, when FNA concentration was 1.48 × 10−2 mg N/L, PN and PS reduced by 20.0% and 10.9%, respectively, indicating that the higher FNA concentration could reduce EPS production. The EPS reduction could be attributed to reduction in the loosely bound (LB) and tightly bound (TB) EPS but not the soluble microbial products (SMP). It was further revealed that higher FNA concentrations up to 1.48 × 10−2 mg N/L consequently mitigate trans-membrane pressure (TMP) rate in terms of dTMP/dt by 25.5% in the nitritation MBR. High throughput sequencing analysis revealed that the increase in FNA led to enrichment of Nitrosomonas but reduction in heterotrophic bacteria. This study showed that the appropriate FNA concentration affected EPS production and hence membrane fouling, leading to the possibility of membrane fouling mitigation by in-situ generated FNA in the nitritation MBR.

Remarkable potential of Na-montmorillonite as a sustainable and eco-friendly material for flocculant studied in the standardized mixing flow

This present study focuses on the ability of montmorillonite, a ubiquitous and non-toxic clay which can be used as an eco-friendly flocculant. For this purpose, coagulation behavior of Polystyrene Amidine Latex (AL) particles with Na-montmorillonite was investigated by the application of standardized mixing method. The flocculation rate of AL particles was assessed as a function of Na-montmorillonite concentration, considering ionic strength and pH. The results showed an enhancement factor (β) ranging from 2 to 5 at an optimal concentration of Na-montmorillonite (∅9.8×10−7). The obtained enhanced rate is attributed to the adsorbing conformation of montmorillonite onto AL particles detected by the combined experiment of electrophoretic mobility and measurement of hydrodynamic layer thickness of clay on AL particles. The finding and established method will be ultimately useful to assess the effect of bio-surfactants or biopolymers which are usually present in microbial extracellular polymeric substances (EPS) interacting with environmental colloidal particles.

Multichannel Biolayer Interferometry to Probe the Binding of Microbial Extracellular Polymeric Substances to Sulfamethoxazole

Microbial extracellular polymeric substances (EPS) can bind to sulfonamides, influencing the removal of antibiotics in biological wastewater treatment systems. However, information about the binding kinetics and affinities of EPS for sulfonamides remains unavailable due to the lack of an effective approach. In this study, biolayer interferometry (BLI), a multichannel sensing technique, is first established to probe the binding of the antibiotic sulfamethoxazole (SMX) to microbial EPS. The influence of environmental conditions, such as pH, ionic strength, and temperature, on this binding interaction is investigated. The results indicate that multichannel BLI can rapidly and accurately determine the association/dissociation rate constants and binding affinities of the binding interactions between EPS and SMX. The high reproducibility of the sensorgrams demonstrates the reliability of the BLI approach. Via comparison of the obtained parameters, the binding interactions between EPS and SMX are significantly improved under acidic conditions compared to those under neutral or alkaline conditions. A higher ionic strength and a lower temperature yield stronger binding between EPS and SMX. BLI analysis allows multichannel operations concurrently, substantially reducing the testing time. The BLI approach developed in this study provides a powerful tool for probing the binding interactions between complex environmental samples.

Microbial extracellular polymeric substances alleviate cadmium toxicity in rice (Oryza sativa L.) by regulating cadmium uptake, subcellular distribution and triggering the expression of stress-related genes

Cadmium (Cd) accumulation in crops causes potential risks to human health. Microbial extracellular polymeric substances (EPS) are a complex mixture of biopolymers that can bind various heavy metals. The present work examined the alleviating effects of EPS on Cd toxicity in rice and its detoxification mechanism. The 100 μM Cd stress hampered the overall plant growth and development, damaged the ultrastructures of both leaf and root cells, and caused severe lipid peroxidation in rice plants. However, applying EPS at a concentration of 100 mg/L during Cd stress resulted in increased biomass, reduced Cd accumulation and transport, and minimized the oxidative damage. EPS application also enhanced Cd retention in the shoot cell walls and root vacuoles, and actively altered the expression of genes involved in cell wall formation, antioxidant defense systems, transcription factors, and hormone metabolism. These findings provide new insights into EPS-mediated mitigation of Cd stress in plants and help us to develop strategies to improve crop yield in Cd-contaminated soils in the future.

Microbial influence on dolomite and authigenic clay mineralisation in dolocrete profiles of NW Australia.

Dolomite (CaMg(CO3 )2 ) precipitation is kinetically inhibited at surface temperatures and pressures. Experimental studies have demonstrated that microbial extracellular polymeric substances (EPS) as well as certain clay minerals may catalyse dolomite precipitation. However, the combined association of EPS with clay minerals and dolomite and their occurrence in the natural environment are not well documented. We investigated the mineral and textural associations within groundwater dolocrete profiles from arid northwest Australia. Microbial EPS is a site of nucleation for both dolomite and authigenic clay minerals in this Late Miocene to Pliocene dolocrete. Dolomite crystals are commonly encased in EPS alveolar structures, which have been mineralised by various clay minerals, including montmorillonite, trioctahedral smectite and palygorskite-sepiolite. Observations of microbial microstructures and their association with minerals resemble textures documented in various lacustrine and marine microbialites, indicating that similar mineralisation processes may have occurred to form these dolocretes. EPS may attract and bind cations that concentrate to form the initial particles for mineral nucleation. The dolomite developed as nanocrystals, likely via a disordered precursor, which coalesced to form larger micritic crystal aggregates and rhombic crystals. Spheroidal dolomite textures, commonly with hollow cores, are also present and may reflect the mineralisation of a biofilm surrounding coccoid bacterial cells. Dolomite formation within an Mg-clay matrix is also observed, more commonly within a shallow pedogenic horizon. The ability of the negatively charged surfaces of clay and EPS to bind and dewater Mg2+ , as well as the slow diffusion of ions through a viscous clay or EPS matrix, may promote the incorporation of Mg2+ into the mineral and overcome the kinetic effects to allow disordered dolomite nucleation and its later growth. The results of this study show that the precipitation of clay and carbonate minerals in alkaline environments may be closely associated and can develop from the same initial amorphous Ca-Mg-Si-rich matrix within EPS. The abundance of EPS preserved within the profiles is evidence of past microbial activity. Local fluctuations in chemistry, such as small increases in alkalinity, associated with the degradation of EPS or microbial activity, were likely important for both clay and dolomite formation. Groundwater environments may be important and hitherto understudied settings for microbially influenced mineralisation and for low-temperature dolomite precipitation.

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.