Composition Of Extracellular Polymeric Substances Research Articles

Extracellular Polymeric Substance Composition Effects on Biosorption for Primary Carbon Diversion

This paper characterizes the composition of extracellular polymeric substances (EPSs) in different types of activated sludge (AS) processes and analyzes the biosorption of soluble organics when waste AS (WAS) is mixed with raw wastewater for primary carbon diversion. The fraction of AS organics identified as EPSs was 26% in a membrane bioreactor (MBR), 54% in conventional AS (CAS), and 51% in a trickling filter/solids contact (TF/SC) process. EPSs were found to be approximately 15% carbohydrates, 40% proteins, 40% humics, and 5% uronics in CAS and MBR AS. Biosorption was not correlated to the organic portion (VSS) of the WAS; however, statistically significant correlations were found for the total amount of EPSs (for TF/SC and CAS) and the protein fraction (for TF/SC and MBR) in the VSS. EPSs from different types of AS biosorbed the same amount of soluble organics, removing 1.43 ± 0.15 (n = 16) mg of soluble chemical oxygen demand (sCOD), and 1.20 ± 0.18 (n = 16) mg of truly soluble COD (ffCOD), per mg of cation exchange resin (CER) total extracted EPSs. Utilizing multiple extraction methods in series (CER–base–sulfide) increased EPS extraction yields by nearly 100% relative to CER alone and indicated different EPS fractionization for CAS (a smaller fraction of carbohydrates and a larger fraction of humics).

Evaluation of autotrophic process influencing extracellular polymeric substances in aerobic membrane bioreactor with expanded ASM model

A mathematical model was developed to predict the formation of both the autotrophic and heterotrophic extracellular polymeric substances (EPS) in the aerobic membrane bioreactor (MBR). Batch experimental results and 45-day operation data on a pilot MBR at a sludge retention time (SRT) of 20 d were used to calibrate and validate the model. Simulated MBR setup results demonstrated the key role of the influent COD and NH4+-N in governing the composition of heterotrophic and autotrophic EPS in the MBR. These results also revealed that the autotrophic EPS process was non-ignorable in the system. According to the autotrophic EPS simulation in the MBR, the EPS yield increased with increasing influent COD/NH4+-N ratio towards a constant level. The EPS yield was significantly influenced by the SRT, attributed to the autotrophic process's impact on EPS. Simulation results revealed a slight increase in EPS yield with an SRT of up to 5 days, followed by a rapid decrease beyond that threshold.

Dissolved organic carbon spurs bacterial-algal competition and phosphorus-paucity adaptation: Boosting Microcystis' phosphorus uptake capacity

Dissolved organic carbon (DOC) can alter the availability of background nutrients by affecting the proliferation of heterotrophic bacteria, which exerts a notable influence on algal growth and metabolism. However, the mechanism of how allochthonous DOC (aDOC) precipitates shifts in bacterial-algal interactions and modulates the occurrence of cyanobacteria blooms remains inadequately elucidated. Therefore, this study investigated the relationship between bacteria and algae under aDOC stimulation. We found that excess aDOC triggered the breakdown and reestablishment of the equilibrium between Microcystis and heterotrophic bacteria. The rapid proliferation of heterotrophic bacteria led to a dramatic decrease in soluble phosphorus and thereby resulted in the inhibition of the Microcystis growth. When the available DOC was depleted, the rapid death of heterotrophic bacteria released large amounts of dissolved phosphorus, which provided sufficient nutrients for the recovery of Microcystis. Notably, Microcystis rejuvenated and showed higher cell density compared to the carbon-absent group. This phenomenon can be ascribed that Microcystis regulated the compositions of extracellular polymeric substances (EPS) and the expression of relevant proteins to adapt to a nutrient-limited environment. Using time of flight secondary ion mass spectrometry (TOF-SIM) and proteomic analysis, we observed an enhancement of the signal of organic matter and metal ions associated with P complexation in EPS. Moreover, Microcystis upregulated proteins related to organic phosphorus transformation to increase the availability of phosphorus in various forms. In summary, this study emphasized the role of DOC in algal blooms, revealing the underestimated enhancement of Microcystis nutrient utilization through DOC-induced heterotrophic competition and providing valuable insights into eutrophication management and control.

The potential effects of N-Acyl homoserine lactones on aerobic sludge granulation during phenolic wastewater treatment

The formation of aerobic granular sludge (AGS) is relatively difficult during the treatment of refractory wastewater, which generally shows small granular sizes and poor stability. The formation of AGS is regulated by N-Acyl homoserine lactones (AHLs)-mediated quorum sensing (QS). However, the potential role of AHLs in AGS formation under the toxic stress of refractory pollutants and the heterogeneity in the distribution and function of AHLs across different aggregates are not well understood. This study investigated the potential effects of AHLs on the formation of AGS during phenolic wastewater treatment. The distribution and succession of AHLs across varying granular sizes and development stages of AGS were investigated. Results showed that AGS was successfully formed in 13 days with an average granular size of 335 ± 39 μm and phenol removal efficiency of >99%. The levels of AHLs initially increased and then decreased. C4-HSL and 3-oxo-C10-HSL were enriched in large granules, suggesting they may play a pivotal role in regulating the concentration and composition of extracellular polymeric substances (EPS). The content of EPS constantly increased to 149.4 mg/gVSS, and protein (PN) was enriched in small and large granules. Luteococcus was the dominant genus constituting up to 62% after the granulation process, and exhibited a strong association with C4-HSL. AHLs might also regulate the bacterial community responsible for EPS production, and pollutant removal, and facilitate the proliferation of slow-growing microorganisms, thereby enhancing the formation of AGS. The synthesis and dynamics of AHLs were mainly governed by AHLs-producing bacterial strains of Rhodobacter and Pseudomonas, and AHLs-quenching strains of Flavobacterium and Comamonas. C4-HSL and 3-oxo-C10-HSL might be the major contributors to promoting sludge granulation under phenol stress and play critical roles in large granules. These findings enhance our understanding of the roles that AHLs play in sludge granulation under toxic conditions.

Mechanistic insight into the aggregation ability of anammox microorganisms: Roles of polarity, composition and molecular structure of extracellular polymeric substances

The chemical characteristics of extracellular polymeric substances (EPS) of anammox bacteria (AnAOB) play a crucial role in the rapid enrichment of AnAOB and the stable operation of wastewater anammox processes. To clarify the influential mechanisms of sludge EPS on AnAOB aggregation, multiple parameters, including the polarity distribution, composition, and molecular structure of EPS, were selected, and their quantitative relationship with AnAOB aggregation was analyzed. Compared to typical anaerobic sludge (anaerobic floc and granular sludge), the anammox sludge EPS exhibited higher levels of tryptophan-like substances (44.82–56.52 % vs. 2.57–39.81 %), polysaccharides (40.02–53.49 mg/g VSS vs. 30.22–41.69 mg/g VSS), and protein structural units including α-helices (20.70–23.98 % vs. 16.48–19.32 %), β-sheets (37.43–42.98 % vs. 25.78–36.72 %), and protonated nitrogen (Npr) (0.065–0.122 vs. 0.017–0.061). In contrast, it had lower contents of β-turns (20.95–27.39 % vs. 28.17–39.04 %). These biopolymers were found to originate from different genera of AnAOB. Specifically, the α-helix-rich proteins were mainly derived from Candidatus Kuenenia, whereas the extracellular proteins related to tryptophan and Npr were closely associated with Candidatus Brocadia. Critically, these EPS components could drive anammox aggregation through interactions. Substantial amounts of tryptophan-like substances facilitated the formation of β-sheet structures and the exposure of internal hydrophobic clusters, which benefited the anammox aggregation. Meanwhile, extracellular proteins with high Npr content played a pivotal role in the formation of mixed protein-polysaccharide gel networks with the electronegative regions of polysaccharides, which could be regarded as the key component in the maintenance of anammox sludge stability. These findings provide a comprehensive understanding of the multifaceted roles of EPS in driving anammox aggregation and offer valuable insights into the development of EPS regulation strategies aimed at optimizing the anammox process.

Extracellular polymeric substances in electroactive biofilms play a crucial role in improving the efficiency of microbial fuel and electrolysis cells.

In microbial electrochemical cells (MECs), electroactive microbial biofilms can transmit electrons from organic molecules to anodes. To further understand the production of anodic biofilms, it is essential to investigate the composition and distribution of extracellular polymeric substance (EPS) in the MECs. In this study, the structure of EPS was examined in microbial electrolysis cells from mixed cultures forming biofilm using carbon fiber fabric anode. EPS was extracted from the anode biofilm of microbial electrolysis cells inoculated with mixed microbial culture. The anode biofilm yielded 0.4mg of EPS, of which 51.2% was humic substance, 16.2% was protein, 12.6% was carbohydrates, and 20% consisted of undetermined substances. Using epifluorescence microscopy, the composition of bacterial cells and their location inside EPS were studied, and the distribution of microbial communities was compared based on current density results in the presence of various carbohydrates. On the electrode surface, bacteria and EPS gathered or overlapped in various locations can affect microbial electrochemical performance. Our findings showed that EPS formation in electroactive biofilms would be important for enhanced efficiency of electricity- or hydrogen-producing microbial electrolysis cells.

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.

Adaptive mechanism of the marine bacterium Pseudomonas sihuiensis-BFB-6S towards pCO2 variation: Insights into synthesis of extracellular polymeric substances and physiochemical modulation

Marine bacteria can adapt to various extreme environments by the production of extracellular polymeric substances (EPS). Throughout this investigation, impact of variable pCO2 levels on the metabolic activity and physiochemical modulation in EPS matrix of marine bacterium Pseudomonas sihuiensis - BFB-6S was evaluated using a fluorescence microscope, excitation-emission matrix (EEM), 2D-Fourier transform infrared correlation spectroscopy (2D-ATR-FTIR-COS), FT-NMR and TGA-DSC. From the results at higher pCO2 levels, there was a substantial reduction in EPS production by 58–62.8 % (DW). In addition to the biochemical composition of EPS, reduction in carbohydrates (8.7–47.6 %), protein (7.1–91.5 %), and lipids (16.9–68.6 %) content were observed at higher pCO2 levels. Functional discrepancies of fluorophores (tyrosine and tryptophan-like) in EPS, speckled differently in response to variable pCO2. The 2D-ATR-FTIR-COS analysis revealed functional amides (CN, CC, CO bending, -NH bending in amines) of EPS were preferentially altered, which led to the domination of polysaccharides relevant functional groups at higher pCO2. 1H NMR analysis of EPS confirmed the absence of chemical signals from H-C-COOH of proteins, α, β anomeric protons, and acetyl group relevant region at higher pCO2 levels. These findings can contribute new insights into the influence of pCO2 on the adaptation of marine microbes in future ocean acidification scenarios.

Synthesizing cationic polymers and tuning their properties for microalgae harvesting

This study reports a facile technique to synthesize and tune the cationic polymer, poly(3-acrylamidopropyl)trimethylammonium chloride (PAPTAC), in terms of molecular weight and surface change for harvesting three microalgae species (Scenedesmus sp., P.purpureum, and C. vulgaris). The PAPTAC polymer was synthesised by UV-induced free-radical polymerisation. Polymer tuning was demonstrated by regulating the monomer concentration (60 to 360 mg/mL) and UV power (36 and 60 W) for polymerisation. The obtained PAPTAC polymer was evaluated for harvesting three different microalgae species and compared to a commercially available polymer. The highest flocculation efficiency for Scenedesmus sp. and P. purpureum was observed at a dosage of 25 mg-polymer/g of dry biomass by using PAPTAC-90, resulting in higher flocculation efficiency than the commercial polymer. Results in this study show evidence of effective neutralisation of the negative charge surface of microalgae cells by the produced cationic PAPTAC polymer and polymer bridging for effective flocculation. The obtained PAPTAC polymer was less effective for harvesting C. vulgaris, possibly due to other factors such as cell morphology and composition of extracellular polymeric substances of at the cell membrane that may also influence harvesting performance.

Interrelation between extracellular polymer substances (EPSs) and MPs in an MBR

Nowadays, microplastics (MPs), as ubiquitous pollutants in aquatic ecosystems, present a major emerging threat. Wastewater treatment plants (WWTPs) are considered a hotspot of MP contamination. In this context, membrane bioreactors (MBRs), which combine conventional activated sludge processes with filtration, serve as an effective technology to remove MPs from wastewater. One of the main factors that affect MBR performance is the amount and composition of extracellular polymeric substances (EPSs) in the mixed liquor (ML). In previous studies carried out at lab-scale with model MPs, it has been found that the presence of MPs in wastewater treatment processes affect the EPS characteristics. In this work, the inter-relationship between EPSs and MPs has been investigated in a MBR at an industrial scale. Samples of the ML were taken from a WWTP during a six-month period and EPSs and MPs were analysed. It was observed that the higher the concentration of MPs, the higher the amount of EPSs were secreted by microorganisms, which seems to indicate that MPs act as an environmental stressor. Additionally, ML samples were centrifuged and the retention of MPs in the centrifuged solid (CS), which mainly depends on the size and morphology of MPs, was evaluated in relation to the amount and composition of EPSs. Remarkably, the concentration of humic acids showed a linear correlation with respect to the percentage of MPs retained in the CS. According to this, a possible mechanism based on hydrophobic interactions has been proposed as being responsible for the retention of MPs in sludge flocs.

Characterization of dual-species biofilms formed by bacteria isolated from milk

This study evaluated biofilm formation of bacteria isolated from raw milk and investigated the composition of extracellular polymeric substances (EPS) using Raman spectroscopy. Biofilms were formed from six isolates on a 96-well microplate at 7 and 25 °C in 1 and 10% reconstituted whole milk. Biofilms were then formed on stainless steel coupons at 7 °C from two isolates identified as strong biofilm producers. Pseudomonas fluorescens, a frequent contaminant of raw milk, forms single or dual-species biofilms with Staphylococcus aureus; however, the sessile cell number of S. aureus remained constant over ten days. Raman spectroscopy identified that EPS composition varied with carbohydrate and protein substrates, the predominant components in P. fluorescens single or dual-species biofilms. Understanding the formation and composition of biofilms at different temperatures and in milk concentrations that simulate the equipment used in the dairy industry is a significant subsidy for establishing adequate sanitary protocols for their mitigation.

Tourmaline mediated enhanced autotrophic denitrification: The mechanisms of electron transfer and Paracoccus enrichment

Autotrophic denitrification (AD) without carbon source is an inevitable choice for denitrification of municipal wastewater under the carbon peaking and carbon neutrality goals. This study first employed sulfur-tourmaline-AD (STAD) as an innovative nitrate removal trial technique in wastewater. STAD demonstrated a 2.23-fold increase in nitrate‑nitrogen (NO3−-N) removal rate with reduced nitrite‑nitrogen (NO2−-N) accumulation, effectively removing 99 % of nitrogen pollutants compared to sulfur denitrification. Some denitrifiers microorganisms that could secrete tyrosine, tryptophan, and aromatic protein (extracellular polymeric substances (EPS)). Moreover, according to the EPS composition and characteristics analysis, the secretion of loosely bound extracellular polymeric substances (LB-EPS) that bound to the bacterial endogenous respiration and enriched microbial abundance, was produced more in the STAD system, further improving the system stability. Furthermore, the addition of tourmaline (Tm) facilitated the discovery of a new genus (Paracoccus) that enhanced nitrate decomposition. Applying optimal electron donors through metabolic pathways and the microbial community helps to strengthen the AD process and treat low carbon/nitrogen ratio wastewater efficiently.

Enhancing anaerobic digestion performance of oxytetracycline-laden wastewater through micro-nano bubble ozonation pretreatment

This study investigated the potential of micro-nano bubble (MNB) ozonation pretreatment to eliminate oxytetracycline (OTC) from wastewater and improve subsequent anaerobic digestion (AD) performance. The findings revealed that MNB ozonation achieved efficient OTC oxidation (>99 % in 60 min), and significantly enhanced methane production by 51 % compared to conventional ozonation (under 30 min of pretreatment). Additionally, MNB ozonation resulted in a decrease in the soluble chemical oxygen demand and reduced volatile fatty acid accumulation compared to conventional ozonation. Furthermore, the study sheds light on the profound impact of OTC and its oxidation by-products on the sludge microbiome. Exposure to OTC and its oxidation by-products resulted in alterations in extracellular polymeric substances composition and led to significant shifts in microbial community structure. This study highlights the promise of MNB ozonation as an effective approach for pharmaceutical pollutant removal and the optimization of AD performance in wastewater treatment, with implications for improved environmental sustainability.

The influence of nutrients on biofilm formation of an ST87 strain of Listeria monocytogenes

Biofilm development by pathogenic organisms plays a pivotal role in certain foodborne illnesses. Listeria monocytogenes, specifically the sequence type 87 (ST87), has been widely identified in China. This study aimed to monitor the dynamic process of biofilm formation by a food-isolated L. monocytogenes ST87 strain under diverse nutritional conditions. Results showed that this strain can consistently exhibit high viable cell counts in both nutrient-rich and nutrient-limited conditions. By utilizing cell counting, we discovered the ability of L. monocytogenes ST87 to form biofilms in various nutritional environments, including beef juice and vegetable juice, maintaining levels above 2 Log10 CFU/cm2. Notably, biofilm formation was expedited under nutrient-limited conditions, with cell counts under nutrient-limited vegetable juice presenting significantly higher than that under the nutrient-rich one. The analysis of the composition of extracellular polymeric substances (EPS) showed a consistent pattern between viable cell count and extracellular protein variation within the biofilms. Moreover, an evaluation of nutritional components (protein, fat, total sugar, ash, and pH) in the culture medium unveiled a positive correlation between extracellular substances and pH, but a negative correlation was identified with other nutritional components.

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.

Exploring nutrient removal mechanisms in column-type SBR with simultaneous nitrification and denitrification

A comprehensive investigation utilized a column-type sequencing batch reactor (SBR) to efficiently remove nutrients throughout various phases of its operational cycle by forming granules. This study assessed the influence and mechanisms of a simultaneous nitrification and denitrification (SND) system employing a column-type sequential batch reactor (SBR). The primary focus was on elucidating the functional groups involved in nitrogen transformation and removal within the extracellular polymeric substances (EPS). The research findings demonstrate the superior performance of the SBR process compared to the control group. It achieved an impressive SND efficiency of 69%, resulting in a remarkable 66% total nitrogen removal. Furthermore, a detailed analysis unveiled that the SBR process had a beneficial impact on the composition and properties of EPS. This impact was observed through increased EPS content and enhanced capacity to transport, convert, and retain nitrogen effectively. Additionally, after initial acclimatization, the SBR process showed its effectiveness in removing nutrients (88–98%) and COD (93%) from the generated wastewater within a hydraulic retention time (HRT) of 6 h. A statistically significant difference between the treatments for the investigated mixing ratios was found by univariate analysis of variance (ANOVA). Machine learning (CatBoost model) was employed to understand each parameter’s relationship and predict the outcomes in measurable quantity. The findings of the SBR trials showed that the concentration of generated wastewater and the HRT impacted the treatment efficiency. However, the effluent may still need other physicochemical processes, such as membrane filtering, coagulation, electrocoagulation, etc., as post-treatment options, even though COD, nutrients, and turbidity have been entirely or significantly effectively removed. Overall, this work offers insightful information on the critical function of the SBR bacterial community in promoting SND.

Time-course adaption strategy of Tetraselmis-based consortia in response to 17α-ethinylestradiol

Estuarine ecosystem constitutes a microenvironment where the abundant green microalga Tetraselmis sp. co-exists with 17α-ethinylestradiol (EE2) pollution. However, the adaption mechanisms of this microalga-based consortia under EE2 shock are rarely recognized. Using extracellular polymeric substance (EPS) characterization, flow cytometry and transcriptomic, this study reveals the time-course response of Tetraselmis-based consortia under EE2 stress. Compared to the insignificant effect of 0.5 mg/L, a high dose of 2.5 mg/L EE2 induces persistent production of reactive oxygen species (ROS) and transiently physiological damages (membrane, chloroplast, organelle morphogenesis, and DNA replication), resulting in cell cycle alteration and division inhibition. These damages could be recovered through active DNA repair and persistently detoxifying processes of enhanced metabolism and ROS quenching. The enhanced EPS production is observed and in line with the significant up-regulation of most key enzymes involved in precursor synthesis and polysaccharides assembling. However, the up-regulation of glycoside hydrolases and most glycosyltransferases, down-regulation of flippases and changed expression of ABC family members indicate the changed EPS composition and synthesis strategy. The resulting increased colloidal polysaccharide is further consumed by associated bacteria whereas protein remains in the co-cultures. These results provide deeper insights into the adverse effects of chemical compounds to microalgae-bacteria and their coadaptation ability.

Insights into the effect of extracellular polymeric substances on anaerobic digestion foaming: From perspectives of composition, hydrophobicity, and functional groups

Foaming is a common issue limiting the efficient and stable operation of food waste anaerobic digesters, and extracellular polymeric substances (EPSs) have been identified as key contributors to the foaming process. To further elucidate the influence mechanism of EPSs on foaming, batch tests were performed under various conditions, including different total solid contents, substrate-to-inoculum ratios, stirring frequencies, and substrate compositions, to induce the production of EPSs with different characteristics. The contributions of EPS composition and hydrophilic and hydrophobic characteristics to the foam formation and foam stabilization processes were analyzed. Hydrophobic EPSs were the main contributor to foam formation (with a correlation coefficient [r] of 0.56 and p < 0.01), while hydrophilic EPSs increased the contribution of hydrophobic EPS by increasing sludge viscosity (r = 0.65, p < 0.01). For foam stabilization, hydrophobic proteins (r = 0.61, p < 0.01) and humic substances (HU) (r = 0.77, p < 0.01) were the main contributors. The former increased foam stability by reducing surface tension (r = 0.63, p < 0.01), while the latter contained functional groups such as amino, hydroxyl, and ether that might enhance the viscosity of the apparent molecular layer of the liquid film, thereby inhibiting foam breakup. Considering that the hydrophobicity of proteins was significantly correlated with the ratio of α-helix to (β-sheet + random coil) in their secondary structure (r = 0.80, p < 0.01), and that HU contributed to foam stabilization owing to the hydration of functional groups, disrupting the secondary structure of proteins and the hydration of HU might contribute to defoaming.

Production and composition of extracellular polymeric substances by a unicellular strain and natural colonies of Microcystis: Impact of salinity and nutrient stress.

The transfer of toxic cyanobacterial Microcystis blooms from freshwater to estuaries constitutes a serious environmental problem worldwide that is expected to expand in scale and intensity with anthropogenic and climate change. The formation and maintenance of Microcystis in colonial form is conditioned to the presence of extracellular polymeric substances (EPS). In this study, we attempted to better understand how the mucilaginous colonial form of Microcystis evolves under environmental stress conditions. In particular, we studied and compared the production and the composition of EPS fractions (attached and free) from natural colonies of a Microcystis bloom and from a unicellular M. aeruginosa strain under salinity and nutrient stress (representing a land-sea continuum). Our results highlighted a greater production of EPS from the natural colonies of Microcystis than the unicellular one under nutrient and combined stress conditions dominated by the attached form. In comparison to the unicellular Microcystis, EPS produced by the colonial form were characterized by high molecular weight polysaccharides which were enriched in uronic acids and hexosamines, notably for the free fraction in response to increased salinities. This complex extracellular matrix gives the cells the ability to aggregate and allows the colonial cyanobacterial population to cope with osmotic shock.

Responses of the microbial community and the production of extracellular polymeric substances to sulfamethazine shocks in a novel two-stage biological contact oxidation system.

The biological contact oxidation reactor is an effective technology for the treatment of antibiotic wastewater, but there has been little research investigating its performance on the sulfamethazine wastewater treatment. In this study, a novel two-stage biological contact oxidation reactor was used for the first time to explore the impact of sulfamethazine (SMZ) on the performance, microbial community, extracellular polymeric substances (EPS), and antibiotic-resistant genes (ARGs). The chemical oxygen demand (COD) and ammonia nitrogen (-N) removal efficiencies kept stable at 86.93% and 83.97% with 0.1-1 mg/L SMZ addition and were inhibited at 3 mg/L SMZ. The presence of SMZ could affect the production and chemical composition of EPS in the biofilm, especially for the pronounced increase in TB-PN yield in response against the threat of SMZ. Metagenomics sequencing demonstrated that SMZ could impact on the microbial community, a high abundance of Candidatus_Promineofilum, unclassified_c__Anaerolineae, and unclassified_c__Betaproteobacteria were positively correlated to SMZ, especially for Candidatus_Promineofilum. Candidatus_Promineofilum not only had the ability of EPS secretion, but also was significantly associated with the primary SMZ resistance genes of sul1 and sul2, which developed resistance against SMZ pressure through the mechanism of targeted gene changes, further provided a useful and easy-implement technology for sulfamethazine wastewater treatment.