Secretion Of Extracellular Polymeric Substances Research Articles

Extracellular polymeric substances induced cell-surface interactions facilitate bacteria transport in saturated porous media

Bacteria often respond to dynamic soil environment through the secretion of extracellular polymeric substances (EPS). The EPS modifies cell surface properties and soil pore-scale hydration status, which in turn, influences bacteria transport in soil. However, the effect of soil particle size and EPS-mediated surface properties on bacterial transport in the soil is not well understood. In this study, the simultaneous impacts of EPS and collector size on Escherichia coli (E. coli) transport and deposition in a sand column were investigated. E. coli transport experiments were carried out under steady-state flow in saturated columns packed with quartz sand with different size ranges, including 0.300–0.425 mm (sand-I), 0.212–0.300 mm (sand-II), 0.106–0.150 mm (sand-III) and 0.075–0.106 mm (sand-IV). Bacterial retention increased with decreasing sand collector size, suggesting that straining played an important role in fine-textured media. Both experiment and simulation results showed a clear drop in the retention rate of the bacterial population with the presence of additional EPS (200 mg L−1) (EPS+). The inhibited retention of cells in sand columns under EPS+ scenario was likely attributed to enhanced bacteria hydrophilicity and electrostatic repulsion between cells and sand particles as well as reduced straining. Calculations of the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) interactions energies revealed that high repulsive energy barrier existed between bacterial cells and sand particles in EPS+ environment, primarily due to high repulsive electrostatic force and Lewis acid-base force, as well as low attractive Lifshitz-van der Waals force, which retarded bacterial population deposition. Steric stabilization of EPS would also prevent the approaching of cells close to the quartz surface and thereby hinder cell attachment. This study was the first to show that EPS reduced bacterial straining in saturated porous media. These findings provide new insight into the functional effects of extrinsic EPS on bacterial transport behavior in the saturated soil environment, e.g., aquifers.

Effect of organic loading on phosphorus forms transformation and microbial community in continuous-flow A2/O process.

A continuous-flow Anaerobic/Anoxic/Oxic (A2/O) system was operated at different organic concentrations to systematically investigate the effect on the nutrient removal, secretion characteristics of extracellular polymer, phosphorus forms transformation and changes in functional flora in this system. The results showed that high organic loading was more conducive to promote the secretion of extracellular polymeric substance (EPS), the increase of polysaccharide content was more obvious compared with protein, the impact of organic loading on the components of loosely bound EPS (LB-EPS) was higher than that of tight-bound EPS (TB-EPS). Phosphorus in sludge floc mainly existed in the form of inorganic phosphorus (IP), and IP mainly existed in the form of apatite inorganic phosphorus (AP). High organic load showed higher phosphorus storage in EPS, and the phosphorus content in EPS was positively correlated with the content of EPS. Non-apatite phosphorus (NAIP) content played an important role in the extracellular dephosphorization. The abundance of Nitrosomonas and Nitrospira responsible for nitrification decreased with the increase in organic loading. The group of denitrifiers was large, and Azospira was the most abundant genus among them. Dechloromonas, Acinetobacter, Povalibacter, Chryseolinea and Pirellula were the functional genera closely associated with phosphorus removal.

Enhancing anaerobic digestion of kitchen wastes via combining ethanol-type fermentation with magnetite: Potential for stimulating secretion of extracellular polymeric substances

Magnetite, a common mineral that is abundant in the soils and sediments, has been widely documented to enhance the anaerobic digestion of organic wastes, whereas the mechanisms of magnetite promoting interspecies electron transfer are still unclear. In this study, under the conditions (ethanol-type fermentation) employed, magnetite stimulated the secretion of extracellular polymeric substances (EPS). Analysis of three-dimensional excitation emission matrix revealed that these EPS secreted in the presence of magnetite were primarily comprised of the redox-active organic functional groups. Electrochemical analysis showed that the EPS secreted with magnetite had the higher electron-accepting and electron-donating capacity than the EPS without magnetite. Syntrophomonas species capable of extracellularly transferring electron were enriched with supplementing magnetite. Together with the increased abundance of Methanospirillum and Methanobacterium species that could proceed direct interspecies electron transfer (DIET), the anaerobic digestion was likely improved due to the establishment of DIET with supplementing magnetite. As a result, anaerobic digestion of kitchen wastes was evidently enhanced. With decreasing the solid retention time to 30 d, the methane production rate only slightly declined to 18 ± 0.8 mL/g-VSS/d in the magnetite-supplemented digester, while almost no methane was detected in the digester without magnetite.

Potential role of nanobubbles in dynamically modulating the structure and stability of anammox granular sludge within biological nitrogen removal process

The generation of visible macrobubbles considerably affects the structure and function of anammox granules in the anammox granular sludge (AnGS) system. However, the existence of nanobubbles (NBs) and their role in maintaining the AnGS structure and stability are unclear because of the complexity of the system and lack of effective analytical methods. In this study, methods for NB analysis and assessment of their effects were developed to investigate the formation and characteristics of NBs in an AnGS system and the effects of NBs on the properties and function of AnGS. The results indicated that dissolved gas supersaturation caused by AnGS generated NBs of 2.75 × 108 bubbles/mL inside an AnGS reactor after running for 300 min at 30 °C. The increasing absolute value of the zeta potential of NBs with time indicated that the NBs in the AnGS system were gradually stable. The size of the stable NBs ranged from 150 nm to 400 nm. NB formation also increased the space and pressure between cells, leading to the breakage of the cell cluster and causing structural changes in granules. Changes in the local granular microstructure caused by NBs were favorable for the porous structure of granules to avoid granular disintegration and flotation caused by the excessive secretion of extracellular polymeric substances blocking gas channels. The formation and stability of NBs penetrating the cell clusters played a crucial role in the formation and stability of nanopores around or inside the cell clusters, further providing a basis for the formation of high-porosity structures and efficient mass transfer of AnGS.

Characterization and significance of extracellular polymeric substances, reactive oxygen species, and extracellular electron transfer in methanogenic biocathode

The microbial electrolysis cell assisted anaerobic digestion holds great promises over conventional anaerobic digestion. This article reports an experimental investigation of extracellular polymeric substances (EPS), reactive oxygen species (ROS), and the expression of genes associated with extracellular electron transfer (EET) in methanogenic biocathodes. The MEC-AD systems were examined using two cathode materials: carbon fibers and stainless-steel mesh. A higher abundance of hydrogenotrophic Methanobacterium sp. and homoacetogenic Acetobacterium sp. appeared to play a major role in superior methanogenesis from stainless steel biocathode than carbon fibers. Moreover, the higher secretion of EPS accompanied by the lower ROS level in stainless steel biocathode indicated that higher EPS perhaps protected cells from harsh metabolic conditions (possibly unfavorable local pH) induced by faster catalysis of hydrogen evolution reaction. In contrast, EET-associated gene expression patterns were comparable in both biocathodes. Thus, these results indicated hydrogenotrophic methanogenesis is the key mechanism, while cathodic EET has a trivial role in distinguishing performances between two cathode electrodes. These results provide new insights into the efficient methanogenic biocathode development.

Response of anammox bacteria to short-term exposure of 1,4-dioxane: Bacterial activity and community dynamics

Anammox process contaminated by 1,4-dioxane was evaluated using sets of batch experiments under different nitrogen loads and 1,4-dioxane concentrations. Toxicity of 1,4-dioxane to anammox consortia was negligible till the level of 200 mg-dioxane/L with a reduction in the total nitrogen (TN) removal efficiency, less than 8% at initial loads of <200 mgTN/L. However, 1,4-dioxane inhibition was also found to be substrate-dependent, where TN removal efficiency was declined by 19.3% at 500 mgTN/L and 200 mg-dioxane/L. The negative synergistic effect was exacerbated in the case of 500 mgTN/L and 2000 mg-dioxane/L, with the minimum TN removal efficiency of 24.1 ± 1.2%. Moreover, the impact of 1,4-dioxane on anammox activity was evaluated in terms of specific anammox activity (SAA), hydrazine dehydrogenase (HDH) activity, and extracellular polymeric substances (EPS). These parameters revealed a significant reduction when 1,4-dioxane surpassed 200 mg/L. Their lowest values of 0.90 ± 0.02 mgTN/gVSS/h (54.7% lower than control), 0.45 ± 0.03 µmol cytochrome-c reduced/min/mg protein (45.1% lower than control), and 74.8 ± 8.5 mg/gVSS (32.6% lower than control) were recorded when anammox bacteria were subjected to initial TN and 1,4-dioxane loads of 200 and 2000 mg/L, respectively. The inhibition mechanism of 1,4-dioxane on the anammox process was expected owing to HDH enzyme inactivation that led to a reduction in SAA and EPS secretion ability. Further, the 16S rRNA analysis revealed that the exposure to 1,4-dioxane caused a significant drop in the dominant anammox genus Candidatus Brocadia, along with a progression of denitrifying bacteria, particularly genus Limnobacter.

Effect of ultraviolet disinfection on the fouling of reverse osmosis membranes for municipal wastewater reclamation

Membrane fouling is a prominent problem that hinders the stable and efficient operation of the reverse osmosis (RO) system for wastewater reclamation. Previous studies showed that chlorine disinfection, which was commonly used in industrial RO systems as pretreatment, could lead to significant change in microbial community structure and resulted in serious biofouling. In order to prevent biofouling during wastewater reclamation, the effect of ultraviolet (UV) disinfection on RO membrane fouling was investigated and the mechanism was also revealed in this study. With the disinfection pretreatment by UV of 20, 40 and 80 mJ/cm2, the bacteria in the feed water were inactivated significantly with a log reduction of 1.11, 2.55 and 3.61-log, respectively. However, RO membrane fouling aggravated with higher UV dosage. Especially, in the group with the UV dosage of 80 mJ/cm2, the normalized RO membrane flux decreased by 15% compared with the control group after 19-day operation. The morphology of the fouled RO membranes indicated serious biofouling in all groups. The analysis on the microbial amount of the foulants showed that the heterotrophic plate counts (HPC) and ATP content on the fouled RO membranes with and without UV disinfection were at the same level. However, the total organic carbon content of the foulants with the UV dosage of 40 and 80 mJ/cm2 was significantly higher than the control group, with higher content of proteins and polysaccharides as indicated by EEM and FTIR spectrum. Microbial community structure analysis showed that some typical UV-resistant bacteria were selected and remained on the RO membrane after disinfection with high UV dosage, including. These residual bacteria after disinfection with high UV dosage showed higher extracellular polymeric substances (EPS) secretion compared with those without UV disinfection, and thus aggravated RO membrane fouling. Thicker EPS could decrease the transmission of UV rays, and thus bacteria with higher EPS secretion might be selected after UV disinfection.

Bacteria enhance the production of extracellular polymeric substances by the green dinoflagellate Lepidodinium chlorophorum

High biomasses of the marine dinoflagellate Lepidodinium chlorophorum cause green seawater discolorations along Southern Brittany (NE Atlantic, France). The viscosity associated to these phenomena has been related to problems in oyster cultivation. The harmful effect of L. chlorophorum might originate from the secretion of Extracellular Polymeric Substances (EPS). To understand whether the EPS are produced by L. chlorophorum or its associated bacteria, or if they are a product of their interaction, batch cultures were performed under non-axenic and pseudo-axenic conditions for three strains. Maximum dinoflagellate cell abundances were observed in pseudo-axenic cultures. The non-sinking fraction of polymers (Soluble Extracellular Polymers, SEP), mainly composed of proteins and the exopolysaccharide sulphated galactan, slightly increased in pseudo-axenic cultures. The amount of Transparent Exopolymer Particles (TEP) per cell increased under non-axenic conditions. Despite the high concentrations of Particulate Organic Carbon (POC) measured, viscosity did not vary. These results suggest that the L. chlorophorum-bacteria interaction could have a detrimental consequence on the dinoflagellate, translating in a negative effect on L. chlorophorum growth, as well as EPS overproduction by the dinoflagellate, at concentrations that should not affect seawater viscosity.

Fatigue of anammox consortia under long-term 1,4-dioxane exposure and recovery potential: N-kinetics and microbial dynamics

Long-term exposure of anammox process to 1,4-dioxane was investigated using periodic anammox baffled reactor (PABR) under different 1,4-dioxane concentrations. The results generally indicated that PABR (composed of 4 compartments) has robust resistance to 10 mg-dioxane/L. The 1st compartment acted as a shield to protect subsequent compartments from 1,4-dioxane toxicity through secretion of high extracellular polymeric substance (EPS) of 152.9 mg/gVSS at 10 mg-dioxane/L. However, increasing 1,4-dioxane to 50 mg/L significantly inhibited anammox bacteria; e.g., ~ 93% of total nitrogen removal was lost within 14 days. The inhibition of anammox process at this dosage was most likely due to bacterial cell lysis, resulting in the decrease of EPS secretion and specific anammox activity (SAA) to 105.9 mg/gVSS and 0.04 mg N/gVSS/h, respectively, in the 1st compartment. However, anammox bacteria were successfully self-recovered within 41 days after the cease of 1,4-dioxane exposure. The identification of microbial compositions further emphasized the negative impacts of 1,4-dioxane on abundance of C. Brocadia among samples. Furthermore, the development of genus Planococcus in the 1st compartment, where removal of 1,4-dioxane was consistently observed, highlights its potential role as anoxic 1,4-dioxane degrader. Overall, long-term exposure to 1,4-dioxane should be controlled not exceeding 10 mg/L for a successful application.

Unveiling the different faces of chlortetracycline in fermentative volatile fatty acid production from waste activated sludge

One of the key challenges of wastewater treatment today is to understand the potential effect of residual pollutants on the management of waste activated sludge (WAS). This study aims to clarify the effect of chlortetracycline (CTC) as a residual antibiotic on the anaerobic fermentation of WAS to produce volatile fatty acids (VFAs). The results show that CTC with a concentration of 10 mg/kg total suspended solids enhances the VFA production by 21.1%. Mechanistically, CTC was found to prompt the secretion of extracellular polymeric substances to provide more substrates for anaerobic fermentation. Meanwhile, CTC stimulates acidification by increasing the activity of acetate kinase, and inhibits methanogenesis by reducing F420 activity, thereby increasing the accumulation of VFAs. This article provides new insights into the behavior of CTC in WAS fermentation, which is essential for resource recovery from WAS containing CTC.

Single-cell Raman micro-spectroscopy for tracking of carotenoids in cyanobacteria exposed to Mn and Zn doped ferrite nanoparticles

Ferrite nanoparticles are increasingly produced and exploited as adsorbents for environmental pollutants. However, their impact on the aquatic microbiota such as cyanobacteria, are not yet investigated. Targeting the environmental monitoring context, in this paper we explored for the first time if any change in the carotenoid signal from cyanobacteria Coelomoron pussilum (AICB 1012) exposed to non-lethal doses of Mn and Zn doped ferrite nanoparticles (NPs) can be associated with the nano-aggression on single-cell level, using micro-Raman spectroscopy. UV–Vis absorption spectroscopy of the bulk culture and single-cell Raman microscopy showed that the carotenoid signal increases relative to the chlorophyll contribution upon exposure of the cells to the Mn-ferrite NPs throughout the 7 days of the experiment. The red-shift and broadening of the strongest carotenoid Raman band arising from (CC) stretching modes indicates the change of carotenoid profile towards increased amount of β-carotene in answer to the NPs stress. The increase of this band intensity relative to the fluorescence background was also observed in Zn-ferrite NPs treatment. Using a simplified and rapid sample preparation procedure, electron microscopy in both transmission and scanning modes, showed greater coverage of the cells by the stable colloidal AgNPs than by the magnetic ferrite NPs. The latter mostly clumped together rather than adhering to the cells. The combined single-cell micro-Raman tracking of physiological response of the unicellular photosynthetic microorganisms coupled with electron microscopy approach to visualise cell-NPs interaction and the extracellular polymeric substance secretion holds the promise for rapid assessment of the NPs-induced environmental stress acting on the unicellular organisms.

In Vitro Effects of Lactobacillus plantarum LN66 and Antibiotics Used Alone or in Combination on Helicobacter pylori Mature Biofilm.

Helicobacter pylori is a gastrointestinal pathogen with high prevalence that harms human health. Studies have shown that H. pylori can form antibiotic-tolerant biofilms, which may interfere with the efficacy of clinical antibiotic therapy. Probiotics can antagonize planktonic and biofilm pathogen cells and thus may play an auxiliary role in H. pylori antibiotic therapy. However, the effects of different probiotic strains and antibiotic combinations on H. pylori biofilms need to be further investigated. We determined the cell viability of H. pylori mature biofilms after treatment with Lactobacillus plantarum LN66 cell-free supernatant (CFS), clarithromycin (CLR), and levofloxacin (LVX) alone or in combination by the XTT method. Biofilm cells were observed by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). Subsequently, protein and polysaccharide concentrations in biofilm extracellular polymeric substances (EPSs) were quantitatively detected by the Bradford method and the phenol-sulfate method. The results showed that LN66 CFS had an eradication effect on mature H. pylori biofilm. When used in combination with CLR, LN66 CFS significantly attenuated the eradication effect of CLR on biofilms; in contrast, when used in combination with LVX, LN66 CFS enhanced the disrupting effect of LVX. We speculate that the different effects of CFS and antibiotic combinations on biofilms may be related to changes in the content of proteins and polysaccharides in EPS and that the combination of CFS and CLR might promote the secretion of EPS, while the combination of CFS and LVX might have the opposite effect. Accordingly, we suggest that supplementation with L. plantarum LN66 may provide additional help when therapy involving LVX is used for clinical H. pylori biofilm eradication, whereas it may impair CLR efficacy when therapy involving CLR is used.

Biofilm formation of Pectobacteriumcarotovorum subsp. carotovorum on polypropylene surface during multiple cycles of vacuum cooling

SummaryDuring vacuum cooling, polypropylene turnover boxes are repeatedly used for containing vegetables for cooling, while Pectobacterium carotovorum subsp. carotovora (Pcc) can form a biofilm on polypropylene adhesion surface. This study evaluated the effects of multiple cycles of vacuum cooling on the morphology and composition of Pcc biofilm formed on polypropylene turnover boxes. Results showed that Pcc biofilm in different growth stages including adhesion, development and mature phases displayed different responses to vacuum cooling. Pcc biofilm in adhesion stage decreased from 106 to 105 CFU cm−2, indicating the positive interference of vacuum cooling on biofilm formation in the initial developmental stage. However, with the increasing of the number of vacuum cooling cycles from 0 to 3, the biomass of Pcc biofilm in the development stage increased from 107 to 108 CFU cm−2 and the polysaccharide secretion increased from 7.96 to 16.7 mg cm−2, showing the promotion of biofilm formation and the secretion of extracellular polymeric substances. Therefore, regular cleansing and sterilisation of turnover boxes are necessary to prevent cross‐contamination during vacuum cooling.

Effects of Fe2O3 nanoparticles on extracellular polymeric substances and nonylphenol degradation in river sediment

In this study, the impact of Fe2O3 nanoparticles (nFe2O3) on microbial extracellular polymeric substances (EPS) and nonylphenol (NP) degradation in sediment were investigated. The results showed that the addition of nFe2O3 lowered the degree of EPS overproduction and the amount of polysaccharides and proteins secreted in NP contaminated sediment. Particularly, the secretion of colloidal EPS (C-EPS) lowered significantly (P < 0.05), and the content of tyrosine-like, tryptophan-like, and soluble microbial by-product-like substances in C-EPS also decreased, leading to a lower aromaticity, humification, and hydrophobicity of C-EPS. Furthermore, with lower C-EPS content in water, NP was adsorbed to sediment more easily, and the weakened toxic effect of NP to bacteria as well as a higher proportion of organic matter degrading microbes stimulated NP degradation. These findings revealed the vital role of nFe2O3 in alleviating NP toxicity to microbes and reducing NP ecological risk in aquatic environments.

Quorum sensing inhibitory effects of vanillin on the biofilm formation of Pseudomonas fluorescens P07 by transcriptome analysis

Pseudomonas fluorescens is an important psychrotrophic food-spoilage bacterium. Quorum sensing (QS) enables bacteria to control various physiological processes. Hence, targeting bacterial QS would be a novel method to improve food quality. In this study, P. fluorescens P07 was treated with vanillin, which showed strong QS inhibitory activity, and its resultant effects on swarming motility, biofilm formation, and extracellular polymeric substance (EPS) secretion were measured. The mechanisms underlying the inhibitory effects were then explored by transcriptomic analysis. The results showed that vanillin had inhibitory effects on swarming motility, biofilm formation, N-acyl-L-homoserine Lactone (AHLs) and EPS secretion of P. fluorescens P07. The result of transcriptionomic tests indicated that the decrease in bacterial biofilm formation was probably due to the influence of vanillin on mobility, adhesion, chemotaxis, EPS secretion, and QS system of the bacteria. Keywords: Pseudomonas fluorescens, quorum sensing, biofilm formation, transcriptome analysis, swarming motility

Microplastics affect the ammonia oxidation performance of aerobic granular sludge and enrich the intracellular and extracellular antibiotic resistance genes

Microplastics (MPs) and antibiotic resistance genes (ARGs), as emerging pollutants, are frequently detected in wastewater treatment plants, and their threats to the environment have received extensive attentions. However, the effects of MPs on the nitrification of aerobic granular sludge (AGS) and the spread patterns of intracellular and extracellular ARGs (iARGs and eARGs) in AGS were still unknown. In this study, the responses of AGS to the exposure of 1, 10 and 100 mg/L of typical MPs (polyvinyl chloride (PVC), polyamide (PA), polystyrene (PS) and polyethylene (PE)) and tetracycline were focused on in 3 L nitrifying sequencing batch reactors. 10 mg/L MPs decreased the nitrification function, but nitrification could recover. Furthermore, MPs inhibited ammonia-oxidizing bacteria and enriched nitrite-oxidizing bacteria, leading partial nitrification to losing stability. PVC, PA and PS stimulated the secretion of extracellular polymeric substances and reactive oxygen species. PE had less negative effect on AGS than PVC, PA and PS. The abundances of iARGs and eARGs (tetW, tetE and intI1) increased significantly and the intracellular and extracellular microbial communities obviously shifted in AGS system under MPs stress. Potential pathogenic bacteria might be the common hosts of iARGs and eARGs in AGS system and were enriched in AGS and MPs biofilms.

Predictive performance of auto-aerated immobilized biomass reactor treating anaerobic effluent of cardboard wastewater enriched with bronopol (2-bromo-2-nitropropan-1,3-diol) via artificial neural network

Anaerobically-pretreated cardboard wastewater (APCW) contains significant residuals of organics, nitrogen species and coarse suspended solids, making the effluent quality not complying for disposal. This is the 1st investigation for treating APCW by an auto-aerated immobilized biomass (AIB) reactor packed with sponge media and ventilated naturally. The optimum hydraulic retention time (HRT) was 4.3 h, achieving CODtotal, CODsoluble, TSS, VSS, TKN, carbohydratetotal, and carbohydratesoluble removal efficiencies of 63.0, 58.8, 71.6, 66.0, 25.5, 38.0, and 33.5%, respectively. The bronopol (2-bromo-2-nitropropan-1,3-diol) supplementation to the APCW feed reduced those removal efficiencies by 20%–40%. The mitigation of bronopol toxicity was illustrated regarding the secretion of extracellular polymeric substances (EPS) to protect the bacterial biomass against the severe environment. The FTIR bands revealed the presence of bound EPS at 1633 and 1403 cm−1 and free EPS at 1035 and 862 cm−1. The alkanes (CH) peaks could be an indicator for the biodegradation of bronopol into formaldehyde by the sponge-retained biomass. An artificial neural network (ANN) model was developed and optimized to predict the COD removal efficiency based on the reactor’s operational conditions, attaining high accuracy (R2: 0.90). The model findings verify the applicability of ANN to simulate the performance of sponge-packing systems, retaining various aerobic, anoxic, and anaerobic species.

Improvement of α-amylase to the metabolism adaptions of soil bacteria against PFOS exposure

Toxicity of perfluoroalkyl substances (PFASs) in soils towards bacteria shows an impact on its ecosystem function. This study aims to obtain insight into the effect of hydrolase (e.g. α-amylase) in soil on metabolism adaptions of bacteria (e.g. Bacillus substilis) against PFOS exposure. Results show that exogenous α-amylase alleviates PFOS toxicity to bacteria growth, disturbance to membrane permeability and stimulation to reactive oxygen species (ROS) production. The mechanisms were owing to that α-amylase strongly influences the strategies of metabolism adaptions of bacteria against PFOS stress. In details, α-amylase prompts bacteria to regulate the secretion of extracellular polymeric substances (EPSs) and the production of metabolic signal (acetic acid), which leads to changes in the physicochemical properties (hydrophilicity, surface charge) of the bacterial surface and the inactivation of the interaction with PFOS, thereby reducing the PFOS toxicity. Molecular simulations show that PFOS combines with Srt A at Gly 53 and Trp 171, which may induce the increase of permeability and changes of surface characteristics. Meanwhile, α-amylase competes with Srt A to bind PFOS at Arg 125 and Lys 176. This competition changes the physicochemical characteristics of PFOS and its bioavailability, further improving the metabolism adaptions of bacteria against PFOS. Altogether, this work provides direct evidences about α-amylase buffering effect of PFOS and demonstrates that the presence of α-amylase affects the essential but complex metabolic response in bacteria triggered by PFOS.

Long-term effect of graphene oxide on the aerobic granular sludge wastewater treatment process

This study investigated the bioreactor performance, production of extracellular polymeric substance (EPS), and microbial activity of a granulated sequencing batch reactor (SBR) by increasing the graphene oxide nanoparticle (GO NP) concentration stepwise. The GO NPs reduced the removal of chemical oxygen demand (COD), ammonia, and phosphorus, whereas the nitrite and nitrate contents of the effluent were kept stable during the experiment. The ammonia-nitrogen (NH4-N) and COD removal rates were deceased considerably from 99% and 95–96.2% and 78.6% at 55 mg/L GO NPs; furthermore, at 115 mg/L GO NPs, the NH4-N and COD removal rates further decreased to 88.5% and 59.3%. The removal of phosphorus decreased even at small concentrations of graphene oxide (GO), and the inhibitory effect enhanced with an increase in the GO NP content. The increased amounts of nanoparticles significantly influenced the microbial activity of aerobic granular sludge (AGS). The specific oxygen uptake rate (SOUR) decreased from 42.04 to 33.14 mg O2/g MLVSS*h, specific ammonia oxidation rate (SAOR) declined from 4.84 to 4.12 mg N/g MLVSS*h, specific phosphorus uptake rate (SPUR), and specific phosphorus release rate (SPRR) significantly decreased from 13.1 and 10.05–8.2 and 8.7 mg P/g MLVSS*h after 98 days. However, the specific nitrite and nitrate reduction rate (SNIRR and SNRR), and the specific nitrite oxidation rate (SNOR) remained relatively stable. The EPS content of sludge was initially 5.95 mg/g MLVSS, but the presence of GO up a concentration of 55 mg/L promoted the secretion of EPS and increased to 11.86 mg/g MLVSS. At higher GO concentrations, the secretion of EPS was inhibited. After 14 days, when the influent synthetic wastewater (SWW) did not contain GO NP, the AGS SBR performance showed a remarkable recovery capability.

Anaerobic co-digestion of chicken manure and cardboard waste: Focusing on methane production, microbial community analysis and energy evaluation

This study aimed to investigate the synergistic effect and microbial community changes between chicken manure (CM) and cardboard (CB) during anaerobic co-digestion. Meanwhile, the energy balance of biogas engineering was extrapolated based on the batch tests. In batch tests, co-digestion system achieved the highest improvement (14.2%) and produced 319.62 mL CH4/gVS with a 65:35 ratio of CB: CM. More extracellular polymeric substance secretion promoted the electron transfer for acidogenesis and more hydrolase was provided with 31.6% improvement. The microbial analysis illustrated that higher acetoclastic Methanosaeta abundance was achieved, leading to 211% enhancement of acetoclastic pathway. Moreover, associated network illustrated that the higher methane production was mainly achieved through matching of hydrolytic bacteria and acidogenesis bacteria. As for energy balance, the synergistic effect increased the energy output by 38% and energy recovery to 46.4%.