Microbial extracellular polymeric substances (EPS) acted as a potential reservoir in responding to high concentrations of sulfonamides shocks during biological wastewater treatment

Exposure to zinc and dialkyldimethyl ammonium compound alters bacterial community structure and resistance gene levels in partial sulfur autotrophic denitrification coupled with the Anammox process

Dialkyldimethyl ammonium compound (DADMAC) is widely used in daily life as a typical disinfectant and often co-exists with the heavy metal zinc in sewage environments. This study investigated the effects of co-exposure to zinc (1 mg/L) and DADMAC (0.2-5 mg/L) on the performance, bacterial community, and resistance genes (RGs) in a partial sulfur autotrophic denitrification coupled with anaerobic ammonium oxidation (PSAD-Anammox) system in a sequencing batch moving bed biofilm reactor for 150 days. Co-exposure to zinc and low concentration (0.2 mg/L) DADMAC did not affect the nitrogen removal ability of the PASD-Anammox system, but increased the abundance and transmission risk of free RGs in water. Co-exposure to zinc and medium-to-high (2-5 mg/L) DADMAC led to fluctuations in and inhibition of nitrogen removal, which might be related to the enrichment of heterotrophic denitrifying bacteria dominated by Denitratisoma. Co-exposure to zinc and high concentration DADMAC (5 mg/L) stimulated the secretion of extracellular polymeric substances and increased the proliferation risk of intracellular RGs in sludge. This study provided insights into the application of PSAD-Anammox system and the ecological risks of wastewater containing zinc and DADMAC.

Molecular spectra and docking simulations investigated the binding mechanisms of tetracycline onto E. coli extracellular polymeric substances

Extracellular polymeric substances (EPS), which were an important fraction of natural organic matter (NOM), played an important role in various environmental processes. However, the heterogeneity, complexity, and dynamics of EPS make their interactions with antibiotics elusive. Using advanced multispectral technology, this study examined how EPS interacts with different concentrations of tetracycline (TC) in the soil system. Our results demonstrated that protein-like (C1), fulvic-like (C2), and humic-like (C3) fractions were identified from EPS. Two-dimensional synchronous correlation spectroscopy (2D-SF-COS) indicated that the protein-like fraction gave faster responses than the fulvic-like fraction during the TC binding process. The sequence of structural changes in EPS due to TC binding was revealed by two-dimensional Fourier Transformation Infrared correlation spectroscopy (2D-FTIR-COS) as follows: 1550 > 1660 > 1395 > 1240 > 1087 cm-1. It is noteworthy that the sensitivity of the amide group to TC has been preserved, with its intensity gradually increasing to become the primary binding site for TC. The integration of hetero-2DCOS maps with moving window 2D correlation spectroscopy (MW2DCOS) provided a unique insight into understanding the correlation between EPS fractions and functional groups during the TC binding process. Moreover, molecular docking (MD) discovered that the extracellular proteins would provide plenty of binding sites with TC through salt bridges, hydrogen bonds, and π-π base-stacking forces. With these results, systematic investigations of the dynamic changes in EPS components under different concentrations of antibiotic exposure demonstrated the advanced capabilities of multispectral technology in examining intricate interactions with EPS in the soil environment.

Differential impacts of organic and inorganic phosphorus on the growth and phosphorus utilization of Microcystis aeruginosa

Phytoplankton growth in freshwater is often limited by the availability of phosphorus (P), and thorough understandings of P availability are essential to prevent algal blooms. However, the differences in bioavailability and utilization mechanisms of different P forms remain unclear, especially whether organophosphorus could be used as P sources. This study investigated the effects of 0.5, 1.0, and 2.0 mg/L P on Microcystis aeruginosa, including dissolved organic P (DOP) (1-hydroxyethane 1,1-diphosphonic acid) and dissolved inorganic P (DIP) (dipotassium phosphate). Compared with DIP, intracellular P content absorbed in DOP treatment was significantly lower. DOP was more conducive to the synthesis of soluble protein and the release of extracellular polymeric substances. Alkaline phosphatase activity was generally enhanced in response to DIP deficiency. Both DIP and DOP promoted carbon uptake to the same extent. DOP groups absorbed carbon to synthesize energy and proteins in response to stress, while DIP groups were mainly used carbon for growth. They all reduced the content of microcystin releasing into the aquatic environment and therefore reduced ecological risk caused by microcystin. Compared with DIP, the expressions of photosynthesis-related genes were significantly down-regulated in DOP group, while the expressions of nucleoside phosphate catabolism, P transporter, and amino acid biosynthesis and metabolism were significantly up-regulated in response to P deficiency environment and the stress of 1.0 mg/L DOP concentration. In summary, the bioavailability of different P forms on cyanobacteria is different, so it is not sufficient to only use total P for assessing environmental risk. P forms should also be considered for risk management of freshwater ecosystems.

Occurrence and mechanism of sulfamethoxazole in alginate-like extracellular polymers from excess sludge

The recovery of biopolymers, particularly alginate-like extracellular polymers, from municipal sludge represents a promising step toward sustainable sludge treatment practices. Originating from wastewater plants in complexly polluted environments, alginate-like extracellular polymers carry potential environmental risks concerning their reuse. This study employs ultrahigh-performance liquid chromatography-tandem mass spectrometry to investigate the distribution coefficients and occurrence of alginate-like extracellular polymers and sulfamethoxazole. Results demonstrate a negative distribution coefficient, suggesting an inhibitory effect on sulfamethoxazole dissolution. The ethanol-extracted alginate-like extracellular polymers exhibits higher sulfamethoxazole levels (approximately 52%) than those obtained via dialysis extraction. Three-dimensional excitation-emission matrix analysis and adsorption studies indicate the absence of tyrosine-like substances in the alginate-like extracellular polymers, unlike in other extracellular polymeric substances. This absence diminishes hydrophobic interactions, highlighting that electrostatic interactions play a more important role. These insights are crucial for understanding the adsorption behavior of alginate-like extracellular polymers and optimizing their large-scale extraction processes.

Role of membrane fouling layer in microbial fuel cell-membrane bioreactor (MFC-MBR) for controlling sulfamethoxazole and corresponding resistance genes

Integrated MFC-MBR systems effectively remove antibiotics and control the release of antibiotic resistance genes (ARGs). However, the fouling layers on membranes can potentially act as reservoirs for ARGs. This study aims to elucidate the roles of membrane fouling layers and levels in influencing sulfamethoxazole (SMX) removal and ARGs control within an MFC-MBR system. Our findings demonstrate that low-intensity bioelectricity (400-500 mV) mitigates membrane fouling rates. The membrane fouling layer significantly contributes (39%-47%) to SMX removal compared to the cathode/anode zones. Higher extracellular polymeric substance (EPS) content and a lower protein/polysaccharide (PN/PS) ratio favor SMX removal by the membrane fouling layer. Across different levels of membrane fouling, the PN/PS ratio rather than EPS concentration plays a crucial role in SMX removal efficiency. The MFC-MBR with low fouling achieved superior SMX removal (69.1%) compared to medium (54.3%) and high fouling conditions (46.8%). The presence of ARGs in the membrane fouling layer increases with fouling formation, with intrinsic ARGs prevailing. Dense membrane fouling layers effectively retain ARGs, thereby reducing the risk of extracellular ARGs (eARGs) diffusion in effluents. These results provide insights into controlling ARGs in MFC-MBR systems and underscore the significant role of membrane fouling layers in antibiotics and ARGs removal.

Distribution characteristics of sulfonamide antibiotics between water and extracellular polymeric substances in municipal sludge

The interaction between extracellular polymeric substances (EPS) in municipal sludge and antibiotics in wastewater is critical in wastewater treatment, resource recovery, and sludge management. Therefore, it is increasingly urgent to investigate the distribution coefficient (Log K) of sulfonamide antibiotics (SAs) in EPS, particularly in sludge-derived dissolved organic carbon (DOC) and aqueous phase systems. Herein, through balance experiments, the concentrations of SAs were determined using alkaline extraction EPS (AEPS) and alginate-like extracellular polymer (ALE) systems, and the Log KDOC values were determined. The results showed that the Log KDOC of AEPS was higher than that of ALE, which exhibited a negative KDOC value, indicating an inhibitory effect on dissolution. For the three SAs studied, the Log KDOC values were in the following order: sulfamethoxazole > sulfapyridine > sulfadiazine. This order can be attributed to the differing physicochemical properties, such as polarity, of the SAs. Three-dimensional excitation-emission matrix fluorescence spectra and fitting results indicated a lack of aromatic proteins dominated by tryptophan and humus-like substances in ALE. Meanwhile, the hydrophobic interaction of aromatic proteins dominated by tryptophan was the main driving force in the binding process between AEPS and SAs.

Physiological responses and molecular mechanisms of biofilm formation induced by extracellular metabolites of euglena in Pseudomonas aeruginosa LNR1 for diesel biodegradation based on transcriptomic and proteomic

Diesel, as a toxic and complex pollutant, is one of the main components in oily wastewater, and poses serious threats to the aquatic environment and the health of organisms. Employing environmentally friendly biostimulants to enhance the metabolic functions of microorganisms is currently the optimal choice to improve the biodegradation of oil-containing wastewater efficiency. This study takes Pseudomonas aeruginosa LNR1 as the target, analyzing the physiological responses and molecular mechanisms of biofilm formation when enhanced by the extracellular metabolites of euglena (EME) for diesel degradation. The results show that EME not only induces auto-aggregation behavior of strain LNR1, forming aerobic suspended granule biofilm, but also promotes the secretion of signaling molecules in the quorum sensing (QS) system. Transcriptomic and proteomic analyses indicate that the stimulatory effect of EME on strain LNR1 mainly manifests in biofilm formation, substance transmembrane transport, signal transduction, and other biological processes, especially the QS system in signal transduction, which plays a significant regulatory role in biofilm formation, chemotaxis, and two-component system (TCS). This study collectively unveils the molecular mechanisms of biostimulant EME inducing strain LNR1 to enhance diesel degradation from different aspects, providing theoretical guidance for the practical application of EME in oily wastewater pollution control.

Study on mechanism of removal of sudden Tetracycline by compound modified biological sand filtration process

The removal of tetracycline from the sewage plant effluents through advanced treatment methods is key to controlling tetracycline levels in the water environment. In this study, modified quartz sands (QS) were used in a biological sand filter to remove tetracycline. The modified QS, with different surface characteristics, were prepared using glass etching technology combined with subsequent chemical modification methods, including hydroxylation treatment, metal ion modification, and amino modification. The adsorption efficiency of hydroxylated QS was higher than that of metal ion modified and amino modified QS, with adsorption efficiencies of 20.4331 mg/kg, 12.8736 mg/kg, and 10.1737 mg/kg, respectively. Results indicated that QS primarily reduce tetracycline through adsorption. Adsorption on ordinary QS fit the pseudo-first-order kinetic model, while adsorption on other modified QS and biofilm-coated QS fit the pseudo-second-order kinetics model. Biodegradation was identified as another mechanism for tetracycline reduction, which fit the zero-order kinetic model. Pseudomonas alcaligenes and unclassified Pseudomonas accounted for 96.6% of the total tetracycline-degrading bacteria. This study elucidates the effectiveness and mechanisms of five types of QS in treating tetracycline from sewage plant effluents. It provides a novel method for tetracycline reduction in real-world wastewater scenarios.

Biotransformation characteristics of tetracycline by strain Serratia marcescens MSM2304 and its mechanism evaluation based on products analysis and genomics

Microbial biotransformation is a recommended and reliable method in face of formidable tetracycline (TC) with broad-spectrum antibacterial activity. Herein, comprehensive characteristics of a newfound strain and its molecular mechanism in process of TC bioremediation were involved in this study. Specifically, Serratia marcescens MSM2304 isolated from pig manure sludge grew well in presence of TC and achieved optimal removal efficiency of 61% under conditions of initial TC concentration of 10 mg/L, pH of 7.0, cell inoculation amount of 5%, and tryptone of 10 g/L as additional carbon. The pathways of biotransformation include EPS biosorption, cell surface biosorption and biodegradation, which enzymatic processes of biodegradation were occurred through TC adsorbed by biofilms was firstly broken down by extracellular enzymes and part of TC migrated towards biofilm interior and degraded by intracellular enzymes. Wherein extracellular polysaccharides in extracellular polymeric substances (EPS) from biofilm of strain MSM2304 mainly performed extracellular adsorption, and changes in position and intensity of CO, =CH and C-O-C/C-O of EPS possible further implied TC adsorption by it. Biodegradation accounting for 79.07% played a key role in TC biotransformation and could be fitted well by first-order model that manifesting rapid and thorough removal. Potential biodegradation pathway including demethylation, dihydroxylation, oxygenation, and ring opening possibly involved in TC disposal process of MSM2304, TC-degrading metabolites exhibited lower toxicity to indicator bacteria relative to parent TC. Whole genome sequencing as underlying molecular evidence revealed that TC resistance genes, dehydrogenases-encoding genes, monooxygenase-encoding genes, and methyltransferase-encoding genes of strain MSM2304 were positively related to TC biodegradation. Collectively, these results favored a theoretical evaluation for Serratia marcescens MSM2304 as a promising TC-control agent in environmental bioremediation processes.

Regulation of ARGs abundance by biofilm colonization on microplastics under selective pressure of antibiotics in river water environment

Interactions of microplastics (MPs) biofilm with antibiotic resistance genes (ARGs) and antibiotics in aquatic environments have made microplastic biofilm an issue of keen scholarly interest. The process of biofilm formation and the degree of ARGs enrichment in the presence of antibiotic-selective pressure and the impact on the microbial community need to be further investigated. In this paper, the selective pressure of ciprofloxacin (CIP) and illumination conditions were investigated to affect the physicochemical properties, biomass, and extracellular polymer secretion of polyvinyl chloride (PVC) microplastic biofilm. In addition, relative copy numbers of nine ARGs were analyzed by real-time quantitative polymerase chain reaction (qPCR). In the presence of CIP, microorganisms in the water and microplastic biofilm were more inclined to carry associated ARGs (2-3 times higher), which had a contributing effect on ARGs enrichment. The process of pre-microplastic biofilm formation might have an inhibitory effect on ARGs (total relative abundance up to 0.151) transfer and proliferation compared to the surrounding water (total relative abundance up to 0.488). However, in the presence of CIP stress, microplastic biofilm maintained the abundance of ARGs (from 0.151 to 0.149) better compared to the surrounding water (from 0.488 to 0.386). Therefore, microplastic biofilm act as abundance buffer island of ARGs stabilizing the concentration of ARGs. In addition, high-throughput analyses showed the presence of antibiotic-resistant (Pseudomonas) and pathogenic (Vibrio) microorganisms in biofilm under different conditions. The above research deepens our understanding of ARGs enrichment in biofilm and provides important insights into the ecological risks of interactions between ARGs, antibiotics, and microplastic biofilm.

Deterioration of sludge characteristics and promotion of antibiotic resistance genes spread with the co-existing of polyvinylchloride microplastics and tetracycline in the sequencing batch reactor

With the continuous increase in microplastics (MPs) and tetracycline (TC) entering wastewater treatment plants (WWTPs) along with sewage, the co-existence of MPs and TC in the biological treatment of wastewater has attracted extensive attention. This study investigated the effect of 1 mg/L polyvinyl chloride (PVC) MPs and 100 ng/L TC co-existing on sequencing batch reactors (SBRs) (S2) treating phenol wastewater in contrast to the control with TC alone (S1). The phenol removal efficiency was significantly inhibited by the co-existence of PVC MPs and TC. Sludge characteristics were also distinctively influenced. The decreased zone sludge velocity (ZSV) and increased sludge volume index (SVI) indicated that the combined effect of PVC MPs and TC deteriorated sludge settleability, which had positive and negative linear correlations with extracellular polymeric substances (EPS) content and the protein (PN)/polysaccharide (PS) ratio, respectively. Moreover, the decreased and increased relative abundances of potential phenol-degraders and antibiotic resistance gene (ARG) carriers may elucidate the inhibition of phenol removal and promotion of ARGs propagation with the co-occurrence of PVC MPs and TC. In addition, the enhanced potential ARGs hosts, loss of the EPS protective effect, and increased membrane permeability induced by reactive oxygen species (ROS) jointly promoted ARGs dissemination in the co-existence of PVC MPs and TC. Notably, the co-occurrence of ARGs and mobile genetic element (MGEs) indicated that the co-existence of PVC MPs and TC promoted the spread of some transposase-associated ARGs mediated by horizontal gene transfer (HGT).

The performance and mechanism of tetracycline and ammonium removal by Pseudomonas sp. DX-21

To remove ammonium and tetracycline (TC) from wastewater, a new strain, DX-21, was isolated and exhibited simultaneous removal ability. The performance of DX-21 in TC removal, its removal mechanism, and the potential toxicities of the degradation products were investigated with genomics, mass spectrometry, density functional theory calculations, quantitative structure-activity relationship analyses, and Escherichia coli exposure experiments. DX-21 exhibited removal of ammonium (9.64 mg·L-1·h-1) via assimilation, and TC removal (0.85 mg·L-1·h-1) primarily occurred through cell surface bio-adsorption and biodegradation. Among the 12 identified degradation products, the majority exhibited lower toxicities than TC. Moreover, potential degradation pathways were proposed, including hydroxylation and deamination. Furthermore, DX-21 possessed TC resistance genes, various oxygenases and peroxidases that could potentially contribute to TC degradation. DX-21 colonized activated sludge and significantly enhanced the biodegradation of TC. Therefore, DX-21 showed potential for treating wastewater containing both ammonium and TC.

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

Introduction

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.

Methods

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).

Results

The chemical oxygen demand (COD) and ammonia nitrogen (NH 4 + -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.

Discussion

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.

Deciphering the distribution and microbial secretors of extracellular polymeric substances associated antibiotic resistance genes in tube wall biofilm

Antibiotics and disinfectants have both been proposed to exert selective pressures on the biofilm as well as affecting the emergence and spread of antibiotic resistance genes (ARGs). However, the transfer mechanism of ARGs in drinking water distribution system (DWDS) under the coupling effect of antibiotics and disinfectants has not been completely understood. In the current study, four lab-scale biological annular reactors (BARs) were constructed to evaluate the effects of sulfamethoxazole (SMX) and NaClO coupling in DWDS and reveal the related mechanisms of ARGs proliferation. TetM was abundant in both the liquid phase and the biofilm, and redundancy analysis showed that the total organic carbon (TOC) and temperature were significantly correlated with ARGs in the water phase. There was a significant correlation between the relative abundance of ARGs in the biofilm phase and extracellular polymeric substances (EPS). Additionally, the proliferation and spread of ARGs in water phase were related to microbial community structure. Partial least-squares path modeling showed that antibiotic concentration may influence ARGs by affecting MGEs. These findings help us to better understand the diffusion process of ARGs in drinking water and provide a theoretical support for technologies to control ARGs at the front of pipeline.

Sub-inhibitory concentrations of ampicillin affect microbial Fe(III) oxide reduction

Antibiotics are ubiquitous in the iron-rich environments but their roles in microbial reduction of Fe(III) oxides are still unclear. Using ampicillin and Geobacter soli, this study investigated the underlying mechanism by which antibiotic regulated microbial reduction of Fe(III) oxides. Results showed that sub-minimal inhibitory concentrations (sub-MIC) of ampicillin significantly affected ferrihydrite reduction by G. soli, with a stimulatory effect at 1/64 and 1/32 MIC and an inhibitory effect at 1/8 MIC. Increasing ampicillin concentration resulted in increasing cell length and decreasing bacterial zeta potential that were beneficial for ferrihydrite reduction, and decreasing outer membrane permeability that was unfavorable for ferrihydrite reduction. The respiratory metabolism ability was enhanced by 1/64 and 1/32 MIC ampicillin and reduced by 1/8 MIC ampicillin, which was also responsible for regulation of ferrihydrite reduction by ampicillin. The ferrihydrite reduction showed a positive correlation with the redox activity of extracellular polymeric substances (EPS) which was tied to the cytochrome/polysaccharide ratio and the content of α-helices and β-sheet in EPS. These results suggested that ampicillin regulated microbial Fe(III) oxide reduction through modulating the bacterial morphology, metabolism activity and extracellular electron transfer ability. Our findings provide new insights into the environmental factors regulating biogeochemical cycling of iron.

Microplastics inhibit biofloc formation and alter microbial community composition and nitrogen transformation function in aquaculture

Biofloc technology, extensively used in intensive aquaculture systems, can prompt the formation of microbial aggregates. Microplastics (MPs) are detected abundantly in aquaculture waters. This study explored the effects of MPs on biofloc formation, microbial community composition and nitrogen transformation function in simulated biofloc aquaculture production systems. The formation process and settling performance of bioflocs were examined. High-throughput sequencing of 16S and 18S rRNA genes was used to investigate the microbial community compositions of bioflocs. Nitrogen dynamics were monitored and further explained from functional genes and microorganisms related to nitrogen transformation by metagenome sequencing. We found that the aggregates consisting of bioflocs and MPs were formed and the systems with MPs had relatively weak settling performance. No significant differences in bacterial diversity (p > 0.05) but significant differences in eukaryotic diversity (p < 0.05) were found between systems without and with MPs. Significant separations in the microbial communities of prokaryotes (p = 0.01) and eukaryotes (p = 0.01) between systems without and with MPs were observed. The peak concentration of nitrite nitrogen (NO₂^--N) in systems with MPs was lower than that in systems without MPs (p_{Control/MPs Low} = 0.02 and p_{Control/MPs High} = 0.03), probably due to the low abundance of hao and affiliated Alphaproteobacteria_bacterium_HGW-Alphaproteobacteria-1 and Alphaproteobacteria_bacterium, but the high abundance of nxrA and affiliated Alphaproteobacteria_bacterium_SYSU_XM001 and Hydrogenophaga_pseudoflava that related to nitrification. The low concentration of NO₂^--N in systems with MPs suggested that the presence of MPs might inhibit ammonia oxidation but promote nitrite oxidation by altering the microbial community structure and function. These results indicated that aggregates consisting of bioflocs and MPs could be formed in aquaculture water, and thus, inhibiting their settlement and altering nitrogen transformation function by affecting the microbial community composition.

Effect of minute amounts of arsenic on the sulfamethoxazole removal and microbial community structure via the SBR system

In this study, the effect of arsenic on the sulfamethoxazole (SMX) removal efficiency and microbial community structure was investigated over 60 days using the SBR process. The results showed that the presence of arsenic had no significant impact on the system performance, the removal efficiencies of two reactors, R1 (the control test) and R2 (with the addition of arsenic), were 13.36 ± 5.71 and 14.20 ± 5.27%, which were attributed to the adsorption of SMX by fulvic acid-like substances and tryptophan-like proteins of extracellular polymeric substances. Compared to the seed sludge, the species number indicated that R2 possessed the richer diversity, while R1 possessed the lower diversity on day 60, which might be relative to the transferring of antibiotic resistance genes (ARGs) in sludge bacterial communities; the minute amounts of arsenic could make the relative levels of Sul1 and Sul2 genes which encode ARGs of sulfonamides in R2 (2.07 and 2.47%) be higher than that in R1 (1.65 and 1.27%), which made the bacterial community of the R2 system more adaptable to SMX stress. Therefore, the minute amounts of arsenic weakened the effect of SMX on the system and enhanced the stability of the microbial community structure.

Extracellular polymeric substances-antibiotics interaction in activated sludge: A review

Antibiotics, the most frequently prescribed drugs, have been widely applied to prevent or cure human and veterinary diseases and have undoubtedly led to massive releases into sewer networks and wastewater treatment systems, a hotspot where the occurrence and transformation of antibiotic resistance take place. Extracellular polymeric substances (EPS), biopolymers secreted via microbial activity, play an important role in cell adhesion, nutrient retention, and toxicity resistance. However, the potential roles of sludge EPS related to the resistance and removal of antibiotics are still unclear. This work summarizes the composition and physicochemical characteristics of state-of-the-art microbial EPS, highlights the critical role of EPS in antibiotics removal, evaluates their defense performances under different antibiotics exposures, and analyzes the typical factors that could affect the sorption and biotransformation behavior of antibiotics. Next, interactions between microbial EPS and antibiotic resistance genes are analyzed. Future perspectives, especially the engineering application of microbial EPS for antibiotics toxicity detection and defense, are also emphatically stressed.

Response of electroactive biofilms from real wastewater to metal ion shock in bioelectrochemical systems

The electrochemical activity of bioelectrochemical systems (BESs) was proven to be dependent on the stability of electroactive biofilms (EABs), but the response of EABs based on real wastewater to external disturbances is not fully known. Herein, we used real wastewater (beer brewery wastewater) as a substrate for culturing EABs and found that current generation, biomass, redox activity and extracellular polymeric substances (EPS) content in those EABs were lower as compared to EABs cultured with synthetic wastewaters (acetate and glucose). However, the EABs from the beer brewery wastewater showed moderate anti-shock resistance capability. The proteins and humic acid in loosely bound EPS (LB-EPS) exhibited a positive linear relationship with current recovery after Ag⁺ shock, indicating the importance of LB-EPS for protecting the EABs. Fluorescence and Fourier transform infrared spectroscopy integrated with two-dimensional correlation spectroscopy verified that the spectra of the protein-like region of LB-EPS changed considerably under the interference of Ag⁺ concentration and the CO group of humic acid or proteins was mainly responsible for binding with Ag⁺ to attenuate its toxicity to the EABs. This is the first study revealing the underlying molecular mechanism of EABs cultured with real wastewater against external heavy metal shock and provides useful insights into enhancing the application of BESs in future water treatment.

Efficient removal of organic compounds in eutrophic water via a synergy of cyanobacterial extracellular polymeric substances and permanganate

This study provides a new thinking for the efficient utilization of permanganate (Mn (VII)) in eutrophic water treatment. Eutrophic water contained a large amount of extracellular polymeric substances (EPS) with reduction and chelation; this study used phenol as typical organic matter and cyanobacteria EPS as a representative EPS to explore the mechanism by which EPS influences the oxidation of phenol by Mn(VII) at pH 5.0-9.0. The results showed that under the condition of pH 5.0-7.0, adding 0.2-10 mg/L EPS to the Mn(VII) system could effectively improve the oxidation efficiency of Mn(VII) for phenol. EPS promoted the continuous formation and stability of in situ EPS-MnO₂ colloids and significantly enhanced the oxidation of Mn(VII). EPS also combined with phenol and increased the electron cloud density to promote the oxidation of phenol by Mn(VII).

Deciphering the role of extracellular polymeric substances in the regulation of microbial extracellular electron transfer under low concentrations of tetracycline exposure: Insights from transcriptomic analysis

Low concentrations of antibiotics can regulate the formation of electroactive biofilms, however, the underlying mechanisms, especially the composition and spatial distribution of extracellular polymeric substances (EPS) and their effects on extracellular electron transfer (EET) process, have not been fully deciphered. Here, the response of EPS of Geobacter sulfurreducens biofilm to low concentrations of tetracycline (μg L^-1 to mg L^-1) was explored, and the impact of such EPS variations on EET efficiency was further elucidated by transcriptomic analysis. Results showed that 0.05 mg L^-1 of tetracycline achieved both beneficial quantitative and spatial regulation of redox-active proteins and non-conducting exopolysaccharides in EPS, while higher concentrations induced negative effects. Moreover, 1 mg L^-1 of tetracycline upregulated multiple exopolysaccharide biosynthesis-related genes, indicating a stress response for cell-protection, while 0.05 mg L^-1 of tetracycline upregulated most direct EET-related gene expressions, resulting in the promoted EET efficiency. Furthermore, 0.05 mg L^-1 of tetracycline selectively enriched Geobacter (45.55% vs 19.55% in control, respectively) from mixed inoculum. This research provides a new insight of how antibiotics at low concentrations regulated EET process through modulation of EPS.

Performance and mechanism of tetracycline removal by the aerobic nitrate-reducing strain Pseudomonas sp. XS-18 with auto-aggregation

The coexistence of multiple pollutants has become a distinctive feature of water pollution. However, there are a few strains that can remove nitrate and tetracycline (TC). Here, the efficiency of strain XS-18 in removing nitrate and TC was analyzed, and the mechanism of tolerance and removal of TC was investigated by infrared spectroscopy, three-dimensional fluorescence spectroscopy, and genome analysis. XS-18 could efficiently remove TC (0.40 mg·L^-1·h^-1) at pH 7.0-11.0 with auto-aggregation. TC was removed via extracellular polymeric substance (EPS) (55.90%) and cell surface (44.10%) adsorption. TC (10 mg/L) could stimulate XS-18 to secrete more polysaccharides and hydrophobic proteins to improve its auto-aggregation ability. The findings also confirmed that TC resistance genes were present. Furthermore, the bacterial flagellum, signal transduction of the chemotactic system and regulatory genes were shown to be related to the auto-aggregation of the strain. XS-18 has potential applications in the treatment of wastewater containing nitrate and TC.

The impact of synthetic musk compounds in biofilms from drinking water bacteria

Musk fragrances have been detected in drinking water (DW) at trace concentrations. However, their impact on the microbial quality of DW has been disregarded. This work provides a pioneer evaluation of the effects of two synthetic musks contaminants, tonalide (AHTN) and galaxolide (HHCB), in microbial biofilms formed on two different surfaces, polyvinyl chloride (PVC) and stainless steel AISI 316 (SS316). Three bacterial species isolated from DW (Acinetobacter calcoaceticus, Burkholderia cepacia and Stenotrophomonas maltophilia), were used to develop 7-day-old single and mixed species biofilms. The impact of musks was assessed directly on biofilms but also on the bacteria motility, biofilm formation ability and biofilm susceptibility to chlorination. AHTN musk caused the most remarkable effects by increasing the cellular density and viability of mixed biofilms, and the extracellular polysaccharides content of biofilms on SS316. Most of the alterations caused by the direct exposure of biofilms to musks were observed when SS316 was used as an adhesion surface. In contrast, the ability to form biofilms and their susceptibility to chlorine were more affected for bacteria from HHCB-exposed biofilms on PVC. The overall results demonstrate that the presence of musks at residual concentrations influences DW bacterial dynamics, with the potential to impact the DW quality and safety. The type of plumbing material may further impact the effects of musks.

Enhanced sulfonamides removal via microalgae-bacteria consortium via co-substrate supplementation

Both co-cultivation and co-substrate addition strategies have exhibited massive potential in microalgae-based antibiotic bioremediation. In this study, glucose and sodium acetate were employed as co-substrate in the cultivation of microalgae-bacteria consortium for enhanced sulfadiazine (SDZ) and sulfamethoxazole (SMX) removal. Glucose demonstrated a two-fold increase in biomass production with a maximum specific growth rate of 0.63 ± 0.01 d^-1 compared with sodium acetate. The supplementation of co-substrate enhanced the degradation of SDZ significantly up to 703 ± 18% for sodium acetate and 290 ± 22% for glucose, but had almost no effect on SMX. The activities of antioxidant enzymes, including peroxidase, superoxide dismutase and catalase decreased with co-substrate supplementation. Chlorophyll a was associated with protection against sulfonamides and chlorophyll b might contribute to SDZ degradation. The addition of co-substrates influenced bacterial community structure greatly. Glucose enhanced the relative abundance of Proteobacteria, while sodium acetate improved the relative abundance of Bacteroidetes significantly.

Trace antibiotics increase the risk of antibiotic resistance genes transmission by regulating the biofilm extracellular polymeric substances and microbial community in the sewer

Sewer is considered a potential hotspot for antibiotic resistance, but the occurrence and proliferation of antibiotic resistance genes (ARGs) under trace antibiotics exposure have received little attention. This work evaluated the effects of tetracycline (TC) and sulfamethoxazole (SMX) individually and in combination in the sewer system and revealed the related mechanisms of ARG proliferation. The relative abundance of tetA and sul1 increased the most under TC and SMX stress, respectively, whereas sul1 increased the most under combined stress. Intl1 was abundant in both the liquid phase and the biofilm, and redundancy analysis confirmed that horizontal gene transfer was the main reason for the proliferation of ARGs. The increase in extracellular polymeric substances (EPS) secretion and the enhancement of the main hydrophobic functional groups facilitated the accumulation of biofilms, which promoted the proliferation of ARGs in biofilms. The relative abundance of most ARGs in the liquid phase was significantly correlated with EPS, protein and tryptophan-like substances. Furthermore, the microbial community structure and diversity affected the proliferation and spread of ARGs in the sewer. These findings contribute to our further understanding of the proliferation and development of ARGs in the sewer and lay the foundation for the front-end control of ARGs.

Bioremediation of sulfonamides by a microalgae-bacteria consortium - Analysis of pollutants removal efficiency, cellular composition, and bacterial community

Antibiotics in wastewaters (e.g., sulfonamides (SAs)) are not effectively removed by the conventional bacterial processes. In this study, a microalgae (Scenedesmus obliquus)-based process was evaluated for the removal of SAs. The maximum removal efficiency of sulfadiazine (SDZ) and sulfamethoxazole (SMX) by the consortium was 5.85% and 40.84%, respectively. The lower SDZ biodegradation efficiency could be due to the difference in the lipophilic degree related to cell binding. The presence of SAs did not significantly inhibit the biomass production of the consortium (1311-1952 mg/L biomass) but led to a 36-51% decrease in total polysaccharide content and an increase in microalgae's protein content, which caused granule formation. The presence of SMX and SDZ resulted in an increase in lipid peroxidation activity with a 6.2 and 23.5-fold increase in malondialdehyde content, respectively. Rhodobacter and Phreatobacter were abundant in the consortium with SAs' presence, while alinarimonas, Catalinimonas and Cecembia were seen in their absence.

Enhanced metronidazole removal by binary-species photoelectrogenic biofilm of microaglae and anoxygenic phototrophic bacteria

High efficient removal of antibiotics during nutriments recovery for biomass production poses a major technical challenge for photosynthetic microbial biofilm-based wastewater treatment since antibiotics are always co-exist with nutriments in wastewater and resist biodegradation due to their strong biotoxicity and recalcitrance. In this study, we make a first attempt to enhance metronidazole (MNZ) removal from wastewater using electrochemistry-activated binary-species photosynthetic biofilm of Rhodopseudomonas Palustris (R. Palustris) and Chlorella vulgaris (C. vulgaris) by cultivating them under different applied potentials. The results showed that application of external potentials of -0.3, 0 and 0.2 V led to 11, 33 and 26-fold acceleration in MNZ removal, respectively, as compared to that of potential free. The extent of enhancement in MNZ removal was positively correlated to the intensities of photosynthetic current produced under different externally applied potentials. The binary-species photoelectrogenic biofilm exhibited 18 and 6-fold higher MNZ removal rate than that of single-species of C. vulgaris and R. Palustris, respectively, due to the enhanced metabolic interaction between them. Application of an external potential of 0V significantly promoted the accumulation of tryptophan and tyrosine-like compounds as well as humic acid in extracellular polymeric substance, whose concentrations were 7.4, 7.1 and 2.0-fold higher than those produced at potential free, contributing to accelerated adsorption and reductive and photosensitive degradation of MNZ.

Recent Advances in Autotrophic Biological Nitrogen Removal for Low Carbon Wastewater: A Review

Due to carbon source dependence, conventional biological nitrogen removal (BNR) processes based on heterotrophic denitrification are suffering from great bottlenecks. The autotrophic BNR process represented by sulfur-driven autotrophic denitrification (SDAD) and anaerobic ammonium oxidation (anammox) provides a viable alternative for addressing low carbon wastewater. Whether for low carbon municipal wastewater or industrial wastewater with high nitrogen, the SDAD and anammox process can be suitably positioned accordingly. Herein, the recent advances and challenges to autotrophic BNR process guided by SDAD and anammox are systematically reviewed. Specifically, the present applications and crucial operation factors were discussed in detail. Besides, the microscopic interpretation of the process was deepened in the viewpoint of functional microbial species and their physiological characteristics. Furthermore, the current limitations and some future research priorities over the applications were identified and discussed from multiple perspectives. The obtained knowledge would provide insights into the application and optimization of the autotrophic BNR process, which will contribute to the establishment of a new generation of efficient and energy-saving wastewater nitrogen removal systems.

Enhancing recovery performance of the toluene-removing biofilter after the short/long interference-shutdown period

In this study, the feasibility of three methods on enhancing the recovery performance of biofilter after the interference and starvation periods was evaluated. Results show that despite the pressure drop risk, supplementation of 7.5% (w/v) Polyethylene glycol-600 (PEG-600) resulted in quick recovery on removal efficiency in both short- and long-term interference shutdown experiments. Tinidazole Tablets (2 mg/L), a Bacteroidetes-specific antibiotic, are more suitable to apply as a one-time shot to improve recovery of biofilter as the second dose of Tinidazole Tablets was no longer effective presumably caused by the increased drug resistance. It is worth noting that the maximum elimination capacity of 134 g/(m³·h) was observed with Pseudomonas putida (P. putida) BRJC1032 addition. The biodegradation kinetic, biological characteristics and microbial community evolution in biofilters were systematically analyzed for finding the suitable methods to enhance recovery performance, which is of great value for the further industrial application of the biofilter technology.

Bacterial biofilm and extracellular polymeric substances in the moving bed biofilm reactor for wastewater treatment: A review

Among the several biofilm-based bioreactors, moving bed biofilm reactors (MBBR) have been extensively used for wastewater treatment due to low operational costs, technical feasibility, and stability. Biofilm forming strains, e.g., Stenotrophomonas maltophila DQ01, achieved 94.21% simultaneous nitrification and denitrification (SND) and 94.43% removal of total nitrogen (TN) at a cycle time of 7 h, and a biofilm consortium consisting of Chryseobacteriumsp. andRhodobactersp. achieved 86.8% removal of total organic carbon (TOC) at hydraulic retention time (HRT) of 24 h using lab-scale MBBR. Modifications in the surface properties of the biocarrier materials achieved 99.5 ± 1.1% chemical oxygen demand (COD) and 93.6 ± 2.3% NH₄⁺-N removal, significantly higher than the conventional commercial carrier. This review article summarizes the application of MBBR technology for wastewater treatment. The importance of bacterial biofilm and extracellular polymeric substances (EPS), anammox-n-DAMO coupled processes, and carrier surface modifications in MBBR technology have also been discussed.

The promotion and inhibition effect of graphene oxide on the process of microbial denitrification at low temperature

This study found that graphene oxide (GO) improved microbial denitrification at low temperatures (~12 °C), and the optimal concentration was 10 mg/L as the removal rate of NO₃-N increased by 17%. At the optimal concentration, GO improved the electron transport system activity of the microbes and enhanced the activity of nitrate reductase and nitrite reductase while exhibited low microbial toxicity. The addition of GO increased the content of tightly bound extracellular polymeric substances (EPS). The results of fluorescence spectrometer indicated that GO accelerated the renewal of bound EPS (B-EPS). Fourier Transform infrared spectroscopy (FTIR) results showed that GO affected the secondary structure of the protein in B-EPS, making B-EPS more hydrophobic and promoting microbial aggregation. B-EPS affected by GO can promote the electron transfer process of microorganisms. However, high concentration (>25 mg/L) of GO may inhibit denitrification by competing for electrons, which was not conducive to denitrification thermodynamically.

Enhancing performance evaluation and microbial community analysis of the biofilter for toluene removal by adding polyethylene glycol-600 into the nutrient solution

Polyethylene glycol-600 (PEG-600), as a carrier for slow release of organic substances, can improve the biocompatibility of packing fillers and the construction of biofilms. The gradient experiments were established to evaluate the feasibility of adding different content of PEG-600 to the biofilter for enhancing toluene removal. In particular, the evolution trend of microbial community embedded in packing fillers was measured by 16S rRNA-based gene sequencing. Results showed that the toluene removal efficiency of biofilter with 7.5% adding content of the PEG-600 was greatly improved, and the maximum elimination capacity of 152 g/(m³·h) was obtained. The introduction of PEG-600 enhanced the tolerance ability to withstand the transient impact loading and intensified the production of extracellular polymeric substances and bonding strength of biofilms. It should be noted that the abundance of Pseudomonas and Steroidobacter at genus level increased significantly. The microbial community evolved into a co-degradation system of toluene and PEG-600.

Response of anammox granules to the simultaneous exposure to macrolide and aminoglycoside antibiotics: Linking performance to mechanism

Antibiotic pollution is becoming increasingly severe due to its extensive use. The potential application of the anaerobic ammonium oxidation (anammox) process in the treatment of wastewater containing antibiotics has attracted much attention. As common antibiotics, spiramycin (SPM) and streptomycin (STM) are widely used to treat human and animal diseases. However, their combined effects on the anammox process remain unknown. Therefore, this study systematically evaluated the response of the anammox process to both antibiotics. The half maximal inhibitory concentrations of SPM and STM were determined. The continuous-flow anammox system could adapt to SPM and STM at low concentrations, while antibiotics at high concentrations exhibited inhibitory effects. When the concentrations reached 5 mg L^-1 SPM and 50 mg L^-1 STM, the nitrogen removal efficiency dramatically decreased and then rapidly recovered within 8 days. Correspondingly, the abundances of dominant bacteria and genes also changed with antibiotic concentrations. In general, the anammox process showed a stable performance and a high resistance to SPM and STM, suggesting that acclimatization by elevating the concentrations was beneficial for the anammox process to obtain resistance to different antibiotics with high concentrations. This study provides guidance for the stable operation of anammox-based biological treatment of antibiotics containing wastewater.

Response of soil bacterial communities to sulfadiazine present in manure: Protection and adaptation mechanisms of extracellular polymeric substances

Extracellular polymeric substances (EPS) play a dominant role in protective biofilms. However, studies exploring the underlying protective mechanism of EPS have mainly focused on activated sludge, whereas their positive roles in protecting soil microbes from environmental stress have not been elucidated. In this study, we revealed the response of soil bacterial communities to various dosages of sulfadiazine (SDZ) present in manure, with a special emphasis on the role of EPS. Sequencing analysis showed that the bacterial community demonstrated stronger symbiotic relationships and weaker competitive interaction patterns to cope with disturbance induced by SDZ. EPS was mainly composed of tyrosine-like and tryptophan-like substances, and moreover, carboxyl, hydroxyl and ether groups were the main functional groups. An adaptation mechanism, namely the enhanced secretion of tryptophan-like substances, could help alleviate the SDZ stress effectively in the biofilms occurring in soil that experienced long-term manure application. Furthermore, the existence of EPS weakened the accumulation of antibiotic resistance genes (ARGs) in soil. Our results for the first time systematically uncover the joint action of biofilm tolerance and ARGs in resisting SDZ stress, which enhances understanding of the protective role of EPS and the underlying mechanisms governing biofilm functions in soil environments.

Interaction between tetracycline and microorganisms during wastewater treatment: A review

Tetracycline (TC) is a commonly used human and veterinary antibiotic that is mostly discharged into wastewater in the form of the parent compounds. At present, wastewater treatment plants (WWTPs) use activated sludge processes that are not specifically designed to remove such pollutants. Considering the biological toxicity of TC in aquatic environment, the migration and fate of TC in the process of wastewater treatment deserve attention. This paper reviews the influence of TC on the functional bacteria in the sludge matrix and the development of tetracycline-resistant genes, and also discusses their adsorption removal rates, their adsorption kinetics and adsorption isotherm models, and infers their adsorption mechanism. In addition, the biodegradation of TC in the process of biological treatment is reviewed. Co-metabolism and the role of dominant bacteria in the degradation process are described, along with the formation of degradation byproducts and their toxicity. Furthermore, the current popular integrated coupling-system for TC degradation is also introduced. This paper systematically introduces the interaction between TC and activated sludge in WWTPs. The review concludes by providing directions to address research and knowledge gaps in TC removal from wastewater.

Enhancing inhibition of disinfection byproducts formation and opportunistic pathogens growth during drinking water distribution by Fe2O3/Coconut shell activated carbon

The effects of biological activated carbon treatment using Fe₂O₃ modified coconut shell-based activated carbon (Fe/CAC) were investigated on the occurrence of opportunistic pathogens (OPs) and formation of disinfection by-products (DBPs) in simulated drinking water distribution systems (DWDSs) with unmodified CAC as a reference. In the effluent of annular reactor (AR) with Fe/CAC, the OPs growth and DBPs formation were inhibited greatly. Based on the differential pulse voltammetry and dehydrogenase activity tests, it was verified that extracellular electron transfer was enhanced in the attached biofilms of Fe/CAC, hence improving the microbial metabolic activity and biological removal of organic matter especially DBPs precursors. Meanwhile, the extracellular polymeric substances (EPS) on the surface of Fe/CAC exhibited stronger viscosity, higher flocculating efficiency and better mechanical stability, avoiding bacteria or small-scale biofilms falling off into the water. Consequently, the microbial biomass and EPS substances amount decreased markedly in the effluent of Fe/CAC filter. More importantly, Fe/CAC did significantly enhance the shaping role on microbial community of downstream DWDSs, continuously excluding OPs advantage and inhibiting EPS production. The weakening of EPS in DWDSs resulted in decrease of microbial chlorine-resistance ability and EPS-derived DBPs precursors supply. Therefore, the deterioration of water quality in DWDSs was inhibited greatly, sustainably maintaining the safety of tap water. Our findings indicated that optimizing biological activated carbon treatment by interface modification is a promising method for improving water quality in DWDSs.

Interaction and removal of oxytetracycline with aerobic granular sludge

Aerobic granular sludge as a promising technology showed great resistance to adverse conditions. However, the interaction between oxytetracycline (OTC) and granular sludge was not studied sufficiently. This study therefore investigated OTC-tolerance ability of incomplete and complete granulation sludge from aspects of simultaneous nutrients removal, sludge characteristics, microbial activity, community changes, and vice versa OTC removal performance. Incomplete granulation sludge showed better denitrification performance and resistance. Whereas, denitrification and phosphorus removal of complete granulation sludge suffered a permanent collapse under 5 mg/L OTC. OTC could be removed by rapid adsorption and slow biodegradation via granular sludge. The EPS, especially TB-PS, played a significant role during the operational period subjected to OTC. The major genera of Lysobacter and Candidatus_Competibacter laid the biological basis for stability and functionality of granules, which acted as the putative contributors for resisting and removing OTC. This study showed that incomplete-granulated sludge qualified more promising application prospect.