Tetracycline exposure shifted microbial communities and enriched antibiotic resistance genes in the aerobic granular sludge

Effect of UV pretreatment on the source control of floR during subsequent biotreatment of florfenicol wastewater

UV photolysis has been recommended as an alternative pretreatment method for the elimination of antibacterial activity of antibiotics against the indicator strain, but the pretreated antibiotic intermediates might not lose their potential to induce antibiotic resistance genes (ARGs) proliferation during subsequent biotreatment processes. The presence of florfenicol (FLO) in wastewater seriously inhibits the metabolic performance of anaerobic sludge microorganisms, especially the positive correlation between UV irradiation doses and ATP content, while it did not significantly affect the organics utilization ability and protein biosynthetic process of aerobic microorganisms. After sufficient UV pretreatment, the relative abundances of floR from genomic or plasmid DNA in subsequent aerobic and anaerobic biotreatment processes both decreased by two orders of magnitude, maintained at the level of the groups without FLO selective pressure. Meanwhile, the abundances of floR under anaerobic condition were always lower than that under aerobic condition, suggesting that anaerobic biotreatment systems might be more suitable for the effective control of target ARGs. The higher abundance of floR in plasmid DNA than in genome also indicated that the potential transmission risk of mobile ARGs should not be ignored. In addition, the relative abundance of intI1 was positively correlated with floR in its corresponding genomic or plasmid DNA (p < 0.05), which also increased the potential horizontal transfer risk of target ARGs. This study provides new insights into the effect of preferential UV photolysis as a pretreatment method for the enhancement of metabolic performance and source control of target ARGs in subsequent biotreatment processes. KEY POINTS: • Sufficient UV photolytic pretreatment efficiently controlled the abundance of floR • A synchronous decrease in abundance of intI1 reduced the risk of horizontal transfer • An appreciable abundance of floR in plasmid DNA was a potential source of total ARGs.

Research progress on the origin, fate, impacts and harm of microplastics and antibiotic resistance genes in wastewater treatment plants

Previous studies reported microplastics (MPs), antibiotics, and antibiotic resistance genes (ARGs) in wastewater treatment plants (WWTPs). There is still a lack of research progress on the origin, fate, impact and hazards of MPs and ARGs in WWTPs. This paper fills a gap in this regard. In our search, we used "microplastics", "antibiotic resistance genes", and "wastewater treatment plant" as topic terms in Web of Science, checking the returned results for relevance by examining paper titles and abstracts. This study mainly explores the following points: (1) the origins and fate of MPs, antibiotics and ARGs in WWTPs; (2) the mechanisms of action of MPs, antibiotics and ARGs in sludge biochemical pools; (3) the impacts of MPs in WWTPs and the spread of ARGs; (4) and the harm inflicted by MPs and ARGs on the environment and human body. Contaminants in sewage sludge such as MPs, ARGs, and antibiotic-resistant bacteria enter the soil and water. Contaminants can travel through the food chain and thus reach humans, leading to increased illness, hospitalization, and even mortality. This study will enhance our understanding of the mechanisms of action among MPs, antibiotics, ARGs, and the harm they inflict on the human body.

Gamma-ray irradiation as an effective method for mitigating antibiotic resistant bacteria and antibiotic resistance genes in aquatic environments

The prevalence of antibiotic resistance genes (ARGs) in municipal wastewater treatment plants (MWTPs) has emerged as a significant environmental concern. Despite advanced treatment processes, high levels of ARGs persist in the secondary effluent from MWTPs, posing ongoing environmental risks. This study explores the potential of gamma-ray irradiation as a novel approach for sterilizing antibiotic-resistant bacteria (ARB) and reducing ARGs in MWTP secondary effluent. Our findings reveal that gamma-ray irradiation at an absorbed dose of 1.6 kGy effectively deactivates all culturable bacteria, with no subsequent revival observed after exposure to 6.4 kGy and a 96-h incubation in darkness at room temperature. The removal efficiencies for a range of ARGs, including tetO, tetA, blaTEM-1, sulI, sulII, and tetW, were up to 90.5% with a 25.6 kGy absorbed dose. No resurgence of ARGs was detected after irradiation. Additionally, this study demonstrates a considerable reduction in the abundances of extracellular ARGs, with the transformation efficiencies of extracellular tetracycline and sulfadiazine resistance genes decreasing by 56.3-81.8% after 25.6 kGy irradiation. These results highlight the effectiveness of gamma-ray irradiation as an advanced and promising method for ARB sterilization and ARG reduction in the secondary effluent of MWTPs, offering a potential pathway to mitigate environmental risks associated with antibiotic resistance.

Effect of antibiotic exposure on the characteristics of activated sludge in a landfill leachate biological treatment system

Changes in the activated sludge performance in an anaerobic/aerobic biological treatment system for leachate was discussed under the condition of tetracycline (TC) exposure. The results show that a low concentration of TC did not have an obvious effect on the removal of chemical oxygen demand (COD) while a high concentration of TC had a certain promoting effect. Under the stimulation of TC, the particle size distribution of anaerobic/aerobic sludge tended to be more uniform, the particle size of anaerobic sludge decreased while the settleability increased; however, the particle size of aerobic sludge increased due to bulking. With the addition of TC, the concentration of most heavy metal ions in sludge samples increased.TC exposure results in the release of a large amount of extracellular polymeric substances (EPS), thus leading to a smoother surface of anaerobic sludge and a rougher surface of aerobic sludge. The high removal efficiency of COD under the high concentration of TC was also presumed to be due to EPS promoting the microbial absorption of anaerobic substances in the leachate. The results clearly showed that TC had a bacteriostatic effect. After antibiotic exposure, the abundance and diversity index of bacteria in each reactor decreased obviously, the microbial community evolved, and the dominant species at the genus and phylum levels of anaerobic/aerobic reactors changed. This study provides a better understanding the effect of TC on activated sludge and has reference value for the management of antibiotic exposure in leachate treatment facilities.

Response of marine anammox bacteria to long-term hydroxylamine stress: Nitrogen removal performance and microbial community dynamics

The response of anammox bacteria to hydroxylamine has not been well explained. Herein, hydroxylamine was long-term added as the sole substrate to marine anammox bacteria (MAB) in saline wastewater treatment for the first time. MAB could tolerate 5 mg/L hydroxylamine. However, MAB activity was inhibited by the high dose of hydroxylamine (40 mg/L), and hydroxylamine removal efficiency was only 3 %. Remarkably, when hydroxylamine reached 20 mg/L, ammonium was produced the most at 2.88 mg/L, mainly by the hydroxylamine and hydrazine disproportionations. Besides, the relative abundance of Candidatus Scalindua decreased from 4.6 % to 0.6 % as the hydroxylamine increased from 0 to 40 mg/L. MAB secreted more extracellular polymeric substances to resist hydroxylamine stress. However, long-term hydroxylamine loading led to the disintegration of MAB granules. This work shed light on the response of MAB to hydroxylamine in saline wastewater treatment.

Effects of voltage and tetracycline on horizontal transfer of ARGs in microbial electrolysis cells

The abuse of antibiotics leads to the production of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs). Microbial electrolysis cells (MECs) have been widely applicated in the field of degrading antibiotics. ARGs were increased via horizontal transfer in single and two-chamber MECs. As one of the critical parameters in MECs, voltage has a particular impact on the ARGs transfer via horizontal transfer. However, there have been few studies of ARGs transfer under the exposure of antibiotics and voltage in MECs. In this study, five concentrations of tetracycline (0, 1, 5, 10, 20 mg/L) were selected to explore the conjugative transfer frequency of plasmid-encoded the ARGs from the donor (E. coli RP4) to receptor (E. coli HB101) in MECs, two voltages (1.5 and 2.0 V) were used to explore the conjugative transfer frequency of ARGs in MECs, then, the transfer of ARGs in MECs under the co-effect of tetracycline and voltage was explored. The results showed that the conjugative transfer frequency of ARGs was significantly increased with the increase of tetracycline concentration and voltage, respectively (p < 0.05). Under the pressure of tetracycline and voltage, the conjugative transfer frequency of ARGs is significantly enhanced with the co-effect of tetracycline and voltage (p < 0.05). The oxidative response induced by electrical stimulation promotes the overproduction of reactive oxygen species and the enhancement of cell membrane permeability of donor and recipient bacteria in MECs. These findings provide insights for studying the spread of ARGs in MECs.

Key genes of electron transfer, the nitrogen cycle and tetracycline removal in bioelectrochemical systems

BACKGROUND

Soil microbial fuel cells (MFCs) can remove antibiotics and antibiotic resistance genes (ARGs) simultaneously, but their removal mechanism is unclear. In this study, metagenomic analysis was employed to reveal the functional genes involved in degradation, electron transfer and the nitrogen cycle in the soil MFC.

RESULTS

The results showed that the soil MFC effectively removed tetracycline in the overlapping area of the cathode and anode, which was 64% higher than that of the control. The ARGs abundance increased by 14% after tetracycline was added (54% of the amplified ARGs belonged to efflux pump genes), while the abundance decreased by 17% in the soil MFC. Five potential degraders of tetracycline were identified, especially the species Phenylobacterium zucineum, which could secrete the 4-hydroxyacetophenone monooxygenase encoded by EC 1.14.13.84 to catalyse deacylation or decarboxylation. Bacillus, Geobacter, Anaerolinea, Gemmatirosa kalamazoonesis and Steroidobacter denitrificans since ubiquinone reductase (encoded by EC 1.6.5.3), succinate dehydrogenase (EC 1.3.5.1), Coenzyme Q-cytochrome c reductase (EC 1.10.2.2), cytochrome-c oxidase (EC 1.9.3.1) and electron transfer flavoprotein-ubiquinone oxidoreductase (EC 1.5.5.1) served as complexes I, II, III, IV and ubiquinone, respectively, to accelerate electron transfer. Additionally, nitrogen metabolism-related gene abundance increased by 16% to support the microbial efficacy in the soil MFC, and especially EC 1.7.5.1, and coding the mutual conversion between nitrite and nitrate was obviously improved.

CONCLUSIONS

The soil MFC promoted functional bacterial growth, increased functional gene abundance (including nitrogen cycling, electron transfer, and biodegradation), and facilitated antibiotic and ARG removal. Therefore, soil MFCs have expansive prospects in the remediation of antibiotic-contaminated soil. This study provides insight into the biodegradation mechanism at the gene level in soil bioelectrochemical remediation.

The presence of copper ions alters tetracycline removal pathway in aerobic granular sludge: Performance and mechanism

This study investigated the removal characteristics of tetracycline (TC) in the presence of copper ions (Cu2+) in aerobic granular sludge by analyzing the TC removal pathway, composition and functional group changes of extracellular polymeric substances (EPS), and microbial community structure. The TC removal pathway changed from cell biosorption to EPS biosorption, and the microbial degradation rate of TC was reduced by 21.37% in the presence of Cu2+. Cu2+ and TC induced enrichment of denitrifying bacteria and EPS-producing bacteria by regulating the expression of signaling molecules and amino acid synthesis genes to increase the content of EPS and -NH2 groups in EPS. Although Cu2+ reduced the content of acidic hydroxyl functional groups (AHFG) in EPS, an increase in TC concentration stimulated the secretion of more AHFG and -NH2 groups in EPS. The long-term presence of TC presence of the relative abundances of Thauera, Flavobacterium and Rhodobacter and improved the removal efficiency.

Fluoroquinolone Residues in the Environment Rapidly Induce Heritable Fluoroquinolone Resistance in Escherichia coli

Extensive antibiotic use increases the environmental presence of their residues and may accelerate the development of antibiotic resistance, although this remains poorly understood at environmentally relevant concentrations. Herein, susceptible Escherichia coli K12 was continuously exposed to five antibiotics at such concentrations for 100 days. The de novo-evolved mutants rapidly obtained fluoroquinolone resistance within 10 days, as indicated by the 4- and 16-fold augmentation of minimum inhibitory concentrations against enrofloxacin and ciprofloxacin, respectively. Moreover, the mutants maintained heritable fluoroquinolone resistance after the withdrawal of antibiotics for 30 days. Genomic analysis identified Asp87Gly or Ser83Leu substitutions in the gyrA gene in the mutants. Transcriptomics data showed that the transcriptional response of the mutants to fluoroquinolones was primarily involved in biofilm formation, cellular motility, porin, oxidative stress defense, and energy metabolism. Homologous recombination and molecular docking revealed that mutations of gyrA primarily mainly conferred fluoroquinolone resistance, while mutations at different positions of gyrA likely endowed different fluoroquinolone resistance levels. Collectively, this study revealed that environmentally relevant concentrations of antibiotics could rapidly induce heritable antibiotic resistance; therefore, the discharge of antibiotics into the environment should be rigorously controlled to prevent the development of antibiotic resistance.

Nanoparticles and antibiotics stress proliferated antibiotic resistance genes in microalgae-bacteria symbiotic systems

The comprehensive effect of exogenous pollutants on the dispersal and abundance of antibiotic-resistance genes (ARGs) in the phycosphere, bacterial community and algae-bacteria interaction remains poorly understood. We investigated community structure and abundance of ARGs in free-living (FL) and particle-attached (PA) bacteria in the phycosphere under nanoparticles (silver nanoparticles (AgNPs) and hematite nanoparticles (HemNPs)) and antibiotics (tetracycline and sulfadiazine) stress using high-throughput sequencing and real-time quantitative PCR. Meanwhile, the intrinsic connection of algae-bacteria interaction was explored by transcriptome and metabolome. The results showed that the relative abundance of sulfonamide and tetracycline ARGs in PA and FL bacteria increased 103-129 % and 112-134 %, respectively, under combined stress of nanoparticles and antibiotics. Antibiotics have a greater effect on ARGs than nanoparticles at environmentally relevant concentrations. Proteobacteria, Firmicutes, and Bacteroidetes, as the primary potential hosts of ARGs, were the dominant phyla. Lifestyle, i.e., PA and FL, significantly determined the abundance of ARGs and bacterial communities. Moreover, algae can provide bacteria with nutrients (carbohydrates and amino acids), and can also produce antibacterial substances (fatty acids). This algal-bacterial interaction may indirectly affect the distribution and abundance of ARGs. These findings provide new insights into the distribution and dispersal of ARGs in microalgae-bacteria symbiotic systems.

Application of spray-dried erythromycin fermentation residue as a soil amendment: antibiotic resistance genes, nitrogen cycling, and microbial community structure

Erythromycin fermentation residue (EFR) after spray drying could be reused as a soil amendment. However, the effects of spray-dried EFR on antibiotic resistance genes (ARGs), nitrogen cycling, and microbial community structure in soil are rarely reported. In this study, a pot experiment was conducted by adding spray-dried EFR to soil. For the application of 1.0% spray-dried EFR, the residual erythromycin (ERY) could be rapidly removed with the half-life of 22.2 d; the total relative abundance of ARGs increased at first, but decreased to the initial level of the control group in the end; genes related to ammonium assimilation (glnA, gltB, gltD), ammonification (gdhA, gudB, cynT, cynS, ncd2), denitrification (narI, narG, narH), assimilatory nitrate reduction (nirA, nasA), and dissimilatory nitrate reduction (nirD) were enriched; soil microbial community structure presented temporary variation. Network analysis showed significant negative correlations between ARGs and nitrogen cycling genes. The addition of 6.0% spray-dried EFR resulted in the amplification of ARGs and inhibition of nitrogen cycling. This work provides new insights into the effects of spray-dried EFR on ARGs, nitrogen cycling, and microbial community structure within the fertilized soil.

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.

Plastisphere showing unique microbiome and resistome different from activated sludge

Plastisphere (the biofilm on microplastics) in wastewater treatment plants (WWTPs) may enrich pathogens and antibiotic resistance genes (ARGs) which can cause risks to the ecological environment by discharging into receiving waters. However, the microbiome and resistome of plastisphere in activated sludge (AS) systems remain inconclusive. Here, metagenome was applied to investigate the microbial composition, functions and ARGs of the Polyvinyl chloride (PVC) plastisphere in lab-scale reactors, and revealed the effects of tetracycline (TC) and/or Cu(II) pressures on them. The results indicated that the plastisphere provided a new niche for microbiota showing unique functions distinct from the AS. Particularly, various potentially pathogenic bacteria tended to enrich in PVC plastisphere. Moreover, various ARGs were detected in plastisphere and AS, but the plastisphere had more potential ARGs hosts and a stronger correlation with ARGs. The ARGs abundances increased after exposure to TC and/or Cu(II) pressures, especially tetracycline resistance genes (TRGs), and the results further showed that TRGs with different resistance mechanisms were separately enriched in plastisphere and AS. Furthermore, the exogenous pressures from Cu(II) or/and TC also enhanced the association of potential pathogens with TRGs in PVC plastisphere. The findings contribute to assessing the potential risks of spreading pathogens and ARGs through microplastics in WWTPs.

Source prevention of halogenated antibiotic resistance genes proliferation: UV/sulfite advanced reduction process achieved accurate and efficient elimination of florfenicol antibacterial activity

The production and consumption of halogenated antibiotics, such as florfenicol (FLO), remain high, accompanied by a large amount of antibiotic-containing wastewater, which would induce the potential proliferation and transmission of antibiotic resistance genes (ARGs) in conventional biological systems. This study revealed that the introduction of reductive species (mainly H) by adding sulfite during UV irradiation process accelerated the decomposition rate of FLO, increasing from 0.1379 min^-1 in the single UV photolytic system to 0.3375 min^-1 in the UV/sulfite system. The enhanced photodecomposition in UV/sulfite system was attributed to the improved dehalogenation performance and additional removal of sulfomethyl group at the site of the benzene ring, which were the representative structures consisting of FLO antibacterial activity. Compared with single UV photolysis, UV/sulfite advanced reduction process saved the light energy requirement by 40 % for the evolutionary suppression of floR, and its corresponding class of ARGs in subsequent biotreatment system was controlled at the level of the negative group. Compared with UV/H₂O₂ and UV/persulfate systems, the decomposition rate of FLO in the UV/S system was the highest and preserved the corresponding carbon source of the coexisting organic compounds for the potential utilization of microbial metabolism in subsequent biotreatment process. These results demonstrated that UV/sulfite advanced reduction process could be adopted as a promising pretreatment option for the source prevention of representative ARGs proliferation of halogenated antibiotics in subsequent biotreatment process.

Fates of antibiotic resistance genes and bacterial/archaeal communities of activated sludge under stress of copper: Gradient increasing/decreasing exposure modes

Effect of copper (Cu) on antibiotic resistance genes (ARGs) and bacterial/archaeal community of activated sludge under gradient increasing (0.5-10 mg/L) or decreasing exposure (10-0.5 mg/L) modes was explored. Here, 29 genes were detected among 48 selected ARGs and mobile gene elements (MGEs). Two exposure modes showed dissimilar effects on ARGs and distribution was more affected by environmental concentrations of Cu, which promoted transmission of ARGs (multiple drug resistance and sulfonamide). Cellular protection was main resistance mechanism, which was less inhibited than efflux pumps. The tnpA-02, as main MGE, interacted closely with ARGs (sul2, floR, etc.). Gradient increasing exposure mode had more effects on bacterial/archaeal structure and composition. Bacteria were main hosts for specific ARGs and tnpA-02, while archaea carried multiple ARGs (cmx(A), adeA, etc.), and bacteria (24.24 %) contributed more to changes of ARGs than archaea (19.29 %). This study clarified the impacts of Cu on the proliferation and transmission of ARGs.

Effects of oxytetracycline on aerobic granular sludge process: Granulation, biological nutrient removal and microbial community structure

Formation of aerobic granular sludge (AGS), process performance and microbial community structure were investigated in lab-scale sequencing batch reactors (SBR) operated without and with oxytetracycline (OTC). Granulation of activated sludge and appearance of AGS was observed in parallel SBRs operated without and with OTC. However, formation of well-settling aerobic granules was relatively faster in the SBR fed with 100 μg/L OTC and observed within 2 weeks of start-up. Ammonium, total nitrogen, and phosphorus removals were quickly established in the AGS cultivated without OTC. In contrast, nitrogen and phosphorus removals were lower in the OTC fed SBR. But, a gradual improvement in nitrogen and phosphorus removals was observed. After 45 days, nitrogen and phosphorous removals were stabilized at 99% and 70%, respectively, due to establishment of OTC-tolerant community. qPCR revealed the impact of OTC on ammonium oxidizing bacteria, polyphosphate accumulating organisms and their enrichment during exposure to OTC. Ammonium and phosphorus were majorly removed via nitritation-denitritation and enhanced biological phosphorus removal (EBPR) pathways, respectively, in the presence of OTC. Brevundimonas (35%), Thaurea (14%) sp. Ca. Competibacter (5.6%), and Ca. Accumulibacter (4.2%) were enriched in OTC-fed AGS. Of the two OTC-tolerant strains isolated, Micrococcus luteus exhibited growth and efficient OTC biotransformation at different OTC concentrations. Moreover, M. luteus was predominantly growing in the form of aggregates. Key traits such as tolerance, biotransformation and high autoaggregation ability allowed a niche for this strain in the granules. This work has important implications in understanding the effect of antibiotics on AGS and designing AGS based treatment for antibiotic-laden wastewaters.

High concentration of ammonia sensitizes the response of microbial electrolysis cells to tetracycline

Microbial electrolysis cell (MEC) is a promising technology for effective energy conversion of wastewater organics to biogas. Yet, in swine wastewater treatment, the complex contaminants including antibiotics may affect MEC performance, while the high ammonia concentration might increase this risk by increasing cell membrane permeability. In this work, the responses of MECs on tetracycline (TC) with low and high ammonia loadings (80 and 1000 mg L^-1) were fully investigated. The TC of 0 to 1 mg L^-1 slightly improved MEC performance in current production and electrochemical characteristics with low ammonia loading, while TC ≥ 4 mg L^-1 started to show negative effects. Generally, the high ammonia loading sensitized MECs to TC concentration, inducing the current and COD removal of MECs to sharply decline with TC ≥ 0.5 mg L^-1. The positive effect of high ammonia loading on MEC due to conductivity increase was counteracted with TC ≥ 1 mg L^-1. The co-contamination of TC and ammonia significantly decreased the bioactivity and biomass of anode biofilm. Although the high concentration of co-existing TC and ammonia inhibited MEC performance, the reactors still obtained positive energy feedback. The network analyses indicated that the effluent suspension contributed much to antibiotic resistance gene (ARG) transmission, while the microplastics (MPs) in wastewater greatly raised the risks of ARGs spreading. This work systematically examined the synergetic effects of TC and ammonia and the transmission of ARGs in MEC operation, which is conducive to expediting the application of MECs in swine wastewater treatment.

The responses of marine anammox bacteria-based microbiome to multi-antibiotic stress in mariculture wastewater treatment

Saline mariculture wastewater containing multi-antibiotics poses a challenge to anaerobic ammonia oxidation (anammox) process. Herein, the halophilic marine anammox bacteria (MAB)-based microbiome was used for treating mariculture wastewater (35‰ salinity) under multi-antibiotics (enrofloxacin + oxytetracycline + sulfamethoxazole, EOS) stress. And the main focus of this study lies in the response of MAB-based microbiome against multi-antibiotics stress. It is found that MAB-based microbiome shows stable community structure and contributes high nitrogen removal efficiency (>90%) even under high stress of EOS (up to 4 mg·L^-1). The relative abundance of main functional genus Candidatus Scalindua, responsible for anammox, had little change while controlling the influent EOS concentration within 4 mg·L^-1, whereas, significantly decreased to 2.23% at EOS concentration of as high as 24 mg·L^-1. As an alternative, antibiotic resistance bacteria (ARB) species Rheinheimera dominated the microbial community of MAB-based biological reactor under extremely high EOS stress (e.g. 24 mg·L^-1 in influent). The response mechanism of MAB-based microbiome consists of extracellular and intracellular defenses with dependence of EOS concentration. For example, while EOS within 4 mg·L^-1 in this study, most of the antibiotics were retained by extracellular polymeric substances (EPS) via adsorption; If increasing the EOS concentration to 8 and even 24 mg·L^-1, part of antibiotics could intrude into the cells and cause the intracellular accumulation of antibiotic resistance genes (ARGs) (total abundance up to 2.44 × 10^-1 copies/16S rRNA) for EOS response. These new understandings will facilitate the practical implementation of MAB-based bioprocess for saline nitrogen- and antibiotics-laden wastewater treatment.

Effects of g-C3N4 on bacterial community and tetracycline resistance genes in two typical sediments in tetracycline pollution remediation

Photocatalysis, as a novel technique, has been widely used for antibiotic pollution remediation in wastewater. In the processes of degradation and removal of antibiotics, the impact of photocatalysts on microenvironment is very important but remains poorly understood. In the present study, the effect of typical photocatalyst g-C3N4 (Graphitic carbon nitride) on microbial community was investigated in two sediment types (riverbed sediment and pig-farm sediment) polluted by tetracycline (TC) in central southern China. The riverbed sediment and pig farm sediment samples were respectively exposed to g-C3N4 (25, 75, 125 mg⋅kg-1) and TC (60, 120, 180 mg⋅L-1) treatments alone or combination for 30 days, respectively. The bacterial community and antibiotic resistance genes (ARGs) of the treated sediments were analyzed by Illumina sequencing and metagenomic sequencing. Studies had shown that: TC, g-C3N4, and TC/g-C3N4 have significant effects on the changes of microbial communities and components in riverbed sediment, but they do not exist in pig farm sediment. The most alterations of microbial taxa were Acidobacteriota, Actinobacteriota, and Desulfobacterota in riverbed sediment, and Elusimicrobiota in the pig farm sediment under various treatments. Through network analysis, it was found that the distribution of microorganisms in the pig farm sediment is more complex and more stable. The addition of g-C3N4 reduced the absolute abundance of ARGs in the two examined sediments, but not significantly changed their relative abundance of ARGs. The g-C3N4 application was beneficial to the removal of TC residues and to the prevention of the generation and transmission of ARGs in sediments. Our results suggested that g-C3N4 was a suitable photocatalyst with excellent application prospect for the removal of TC residues and the control of ARGs in environment.

Microalgae simultaneously promote antibiotic removal and antibiotic resistance genes/bacteria attenuation in algal-bacterial granular sludge system

This study investigated the effects of microalgae growth on antibiotic removal and the attenuation of antibiotic resistance genes (ARGs)/ARGs host bacteria in algal-bacterial granular sludge (ABGS) system. In the presence of tetracycline (TC) and sulfadiazine (SDZ) mixture (2-4 mg/L), microalgae could grow on bacterial granular sludge (BGS) to form ABGS, with a chlorophyll-a content of 7.68-8.13 mg/g-VSS being achieved. The removal efficiencies of TC and SDZ by ABGS were as high as 79.0 % and 94.0 %, which were 4.3-5.0 % higher than those by BGS. Metagenomic analysis indicated that the relative abundances of TC/SDZ- related ARGs and mobile genetic elements (MGEs) in BGS were 56.1 % and 22.1 % higher than those in ABGS. A total of 26 ARGs were detected from the granules, and they were identified to associate with 46 host bacteria. 13 out of 26 ARGs and 13 out of 46 hosts were shared ARGs and hosts, respectively. The total relative abundance of host bacteria in BGS was 30.8 % higher than that in ABGS. Scenedesmus and Chlorella were the dominant microalgae that may reduce the diversity of ARGs hosts. Overall, ABGS is a promising biotechnology for antibiotic-containing wastewater treatment.

Anaerobic electrochemical membrane bioreactor effectively mitigates antibiotic resistance genes proliferation under high antibiotic selection pressure

The spread of antibiotics and antibiotic resistance genes (ARGs) in environments has posed potential threats to public health. Unfortunately, conventional biological wastewater treatment technologies generally show insufficient removal of antibiotics and ARGs. Bioelectrochemical systems, which can effectively degrade refractory organic pollutants via enhancing microbial metabolisms through electrochemical redox reaction, may provide an alternative for the control of antibiotics and ARGs. Herein, an anaerobic electrochemical membrane bioreactor (AnEMBR) was conducted by combining bioelectrochemical system and anaerobic membrane bioreactor to treat antibiotic-containing wastewater. The AnEMBR at open circuit showed stable CH4 production and high removal of COD and chlortetracycline (CTC) in treating 2.5-15 mg/L CTC. However, increasing CTC to 45 mg/L completely inhibited the methanogenesis of AnEMBR at open circuit. After applying external voltage in AnEMBR, the performances of AnEMBR were significantly improved (e.g., increased CH4 production and CTC removal). Moreover, CTC exposure significantly increased the relative abundances of ARGs in sludge, supernatant, and effluent in AnEMBR at open circuit. Applying voltage greatly attenuated the total relative abundances of ARGs in the supernatant and effluent of AnEMBR compared to those at open circuit. This could be attributed to the enrichment of tetracycline degradation gene tetX, which greatly enhanced the removal of CTC by the AnEMBR and thus reduced the selective pressure of CTC on the microorganisms in supernatant and effluent for ARGs proliferation. These results would provide an effective wastewater treatment technology for treating high-level antibiotic-containing wastewater to mitigate the potential risk of ARGs and antibiotics spread in receiving water body.

Step feed mode synergistic mixed carbon source to improve sequencing batch reactor simultaneous nitrification and denitrification efficiency of domestic wastewater treatment

The limited efficiency of nitrogen removal has traditionally hindered wide application of simultaneous nitrification and denitrification (SND) technology. Here, the nitrogen removal characteristics of a sequencing batch reactor were studied by adopting a strategy of a step-feeding mode, synergistic regional oxygen limitation, and a mixed carbon source. The changes of the microbial population succession and nitrogen metabolism functional genes were analyzed. This strategy provided a favorable level of dissolved oxygen and continuous carbon sources for driving the denitrification process. The total nitrogen removal efficiency and SND rate reached 92.60% and 96.49%, respectively, by regulating the ratio of sodium acetate to starch in the step feed to 5:1. This procedure increased the relative abundance of denitrifying functional genes and induced the growth of a variety of traditional denitrifying bacteria and aerobic denitrifying bacteria participating in the process of nitrogen removal. Overall, this work offers a new strategy for achieving efficient SND.

The Dual Roles of Nano Zero-Valent Iron and Zinc Oxide in Antibiotics Resistance Genes (ARGs) SPREAD in Sediment

Nanoparticles (NPs) are widely used and ubiquitous in the environment, but the consequences of their release into the environment on antibiotics resistance genes (ARGs), microbial abundance, and community, are largely unknown. Therefore, this study examined the effect of nano zero-valent iron (nZVI) and zinc oxide (nZnO) on tetracycline resistance genes (tet-ARGs) and class 1 integron (intI1) in sediment under laboratory incubation. The coexistence of NPs and tetracycline (TC) on tet-ARGs/intI1 was also investigated. It was found that nZVI and nZnO promoted tet-ARGs/intI1 abundance in sediment without TC but reduced the inducing effect of TC on tet-ARGs/intI1 in sediment overlaid with TC solution. Without TC, nZVI, intI1, and the bacterial community could directly promote tet-ARGs spread in nZVI sediment, while intI1 and bacterial abundance were the most directly important reasons for tet-ARGs spread in nZnO sediment. With TC, nZVI and bacterial community could reduce tet-ARGs abundance in nZVI sediment, while nZnO and bacterial community could directly promote tet-ARGs in nZnO sediment. Finally, these findings provided valuable information for understanding the role of NPs in promoting and reducing ARGs in the environment.

Antibiotic resistance gene profile in aerobic granular reactor under antibiotic stress: Can eukaryotic microalgae act as inhibiting factor?

Antibiotic resistance gene (ARG) pollution is critical environmental problem, and horizontal gene transfer acts as a driving evolutionary force. In theory, due to the phylogenetic distance between eukaryotes and prokaryotes, eukaryotic microalgae can be a natural barrier that plays a negative role in ARG transfer among the symbiotic bacteria to decrease ARG abundance in sludge during wastewater treatment. However, this hypothesis is far from proven and needs to be tested experimentally, so this study investigated the influence of eukaryote microalgae (Scenedesmus) on the ARG profile of symbiotic bacteria based on aerobic granular reactor. The results indicated that Scenedesmus symbiosis could affect ARG diversity of bacteria, and the detected numbers of ARG in aerobic granular sludge (AG) group and algae-bacteria granular consortia (AAG) group were 45-53 and 44-47, respectively. In terms of relative abundance, after target microalgae symbiosis, the total abundance of ARGs significantly decreased from 1.17 × 10°, 2.69 × 10° and 1.36 × 10^-1 to 6.53 × 10^-1, 9.64 × 10^-1 and 1.04 × 10^-1 in the systems with the addition of streptomycin, azithromycin and vancomycin, respectively (P < 0.05), yet there was no significant difference between AG and AAG under the stress of ampicillin, sulfamethazine and tetracycline (P > 0.05). Redundancy analysis showed that the eukaryotic microalgae were significant factor explaining the change in ARG relative abundance (P < 0.05), which contributed 15.3% of ARG variation. Furthermore, the results show that, except for the tetracycline treatment system, the total relative abundances of MGEs in the AAG under the stress of the other five antibiotics were 3.54 × 10^-2-7.13 × 10^-1, which were all significantly lower than those in the AG (8.38 × 10^-2-1.59 × 10°). There was a more significant positive correlation relationship between ARGs and mobile genetic elements (MGEs) than that between ARGs and dominated bacteria.

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.

The dissimilarity of antibiotic and quorum sensing inhibitor on activated sludge nitrification system: Microbial communities and antibiotic resistance genes

Effects of antibiotics (azithromycin, AZM, 1-40 mg/L) and quorum sensing inhibitor (QSI, 2(5H)-furanone, 1-40 mg/L) combined pollution with environmental concentration of copper on bacterial/archaeal community and antibiotic resistance genes (ARGs) in activated sludge system were explored. QSI inhibited nitrification more obviously than AZM. AZM and QSI were synergistic inhibitions on bacterial diversity, and AZM inhibited bacterial compositions more than QSI. While, QSI had more impacts on archaeal diversity/compositions. Less interactions among bacteria and archaea communities with Aquimonas as keystone genus. Functional differences in bacteria/archaea communities were little, and AZM had more effects on metabolism. AZM mainly affected nitrifying bacteria (Candidatus Nitrospira nitrificans and Nitrosomonas). Specific denitrifying bacteria were enriched by AZM (Brevundimonas, 1.76-31.69%) and QSI (Comamonas, 0.61-9.61%), respectively. AZM enriched ARGs more easily than QSI and they were antagonistic to proliferation of ARGs. Bacteria were main hosts of ARGs (macrolide-lincosamide-streptogramin B, other/efflux, etc.) and archaea (Methanosphaerula, Methanolobus) carried multiple ARGs.

Triclosan enriched resistance genes more easily than copper in the presence of environmental tetracycline in aerobic granular sludge system

Triclosan (TCS) and copper (Cu²⁺) were exposed to aerobic granular sludge (AGS) system treating wastewater containing environmental tetracycline, respectively, to explore the different biochemical responses, more importantly, the fates of resistance genes (RGs) in AGS system. The results showed that TCS and Cu²⁺ could significantly inhibit the N and P removal in AGS system by reducing several key functional genes, including amoA gene of ammonia-oxidizing bacteria, Nitrospira and phosphorus accumulating organisms 16S rRNA genes. TCS caused higher degree of RGs' enrichment than Cu²⁺, which made the average total relative abundance of RGs of 1.38 ± 0.73 and 0.78 ± 0.24 in TCS and Cu system, respectively. Cu²⁺ could induce a wider range of horizontal gene transfer than TCS, leading to the detections of more potential hosts harboring RGs in Cu system. Cu system seemed to have stronger repair, immunity and defense ability than TCS system, which enabled it to have sufficient ability to trigger protection mechanism to realize self-protection, eventually the RGs also were controlled. Integron (intI1 and intI3) and plasmids (trb-C and IncQ) might cooperate with microorganisms and water quality parameters to enhance the enrichment of RGs in TCS system, however this interaction among various environmental factors was not obvious in Cu system, which might be responsible for the lower abundance of RGs. The increasing levels of TCS and Cu²⁺ in wastewater should be paid more attentions during the treatment of wastewater containing environmental tetracycline by AGS system. Especially for TCS, it had the ability to enrich RGs more easily than Cu²⁺, which should be prevented from entering wastewater treatment plants as far as possible, to avoid more serious proliferation and dissemination of various RGs.

Coexistence of silver ion and tetracycline at environmentally relevant concentrations greatly enhanced antibiotic resistance gene development in activated sludge bioreactor

Antibiotic resistance has become a global public health problem. Recently, various environmental pollutants have been reported to induce the proliferation of antibiotic resistance. However, the impact of multiple pollutants (e.g., heavy metals and antibiotics), which more frequently occur in practical environments, is poorly understood. Herein, one widely distributed heavy metal (Ag⁺) and one frequently detected antibiotic (tetracycline) were chosen to investigate their coexisting effect on the proliferation of antibiotic resistance in the activated sludge system. Results show that the co-occurrence of Ag⁺ and tetracycline at environmentally relevant concentrations exhibited no distinct inhibition in reactor performances. However, they inhibited the respiratory activity by 42%, destroyed the membrane structure by 218%, and increased membrane permeability by 29% compared with the blank control bioreactor. Moreover, the relative abundances of target antibiotic resistance genes (ARGs) (e.g., tetA, bla_TEM-1, and sulII) in effluent after exposure of coexisting Ag⁺ and tetracycline were increased by 92-1983% compared with those in control reactor, which were 1.1-4.3 folds higher than the sum of the sole ones. These were possibly attributed to the enrichments of antibiotic-resistant bacteria. The results would illumine the coexisting effect of heavy metals and antibiotics on the dissemination of ARGs in activated sludge system.

Tetracycline removal in granulation: Influence of extracellular polymers substances, structure, and metabolic function of microbial community

Tetracycline is a potentially hazardous residual antibiotic detected in various sewages. High concentration (mg/L) of tetracycline is found in pharmaceutical/hospital wastewater and wastewater derived from livestock and poultry. So far, only antibiotics in μg/L level have been reported in granulation of aerobic sludge during wastewater treatment, but its effects in high concentration are rarely reported. In this study, the influence of tetracycline in high concentration (∼2 mg/L) on the formation of granular sludge, structure, and metabolic function of the microbial community during the granulation of aerobic sludge was investigated to improve the understanding of the aerobic granular sludge formation under high-level of tetracycline. The role of extracellular polymers substances (EPSs) derived from granular sludge in the granulation and tetracycline removal process was also investigated, showing that tetracycline improved the relative hydrophobicity, flocculability and protein/polysaccharide ratio of EPSs, accelerating the granulation of sludge. Succession of microbial communities occurred during the domestication of functional bacteria present in the sludge and was accompanied with regulation of metabolic function. The addition of tetracycline lead to an increase of tetracycline-degrading bacteria or antibiotic resistance genus. Those findings provide new perspectives of the influence of tetracycline on aerobic sludge granulation and the removal mechanism of tetracycline.

Response of microbial communities based on full-scale classification and antibiotic resistance genes to azithromycin and copper combined pollution in activated sludge nitrification laboratory mesocosms at low temperature

This study aimed to investigate the short-term response of abundant-rare genera and antibiotic resistance genes (ARGs) to azithromycin (AZM, 0.05-40 mg/L) and copper (1 mg/L) combined pollution in activated sludge nitrification system at low temperature. Nitrification was as expected inhibited in stress- and post-effects periods under AZM concentration higher than 5 mg/L. Abundant and rare taxa presented dissimilar responses based on full-scale classification. Conditionally rare or abundant taxa (CRAT) were keystone taxa. Relative abundance of ammonia-oxidizing archaea increased, and three aerobic denitrifying bacteria (Brevundimonas, Comamonas and Trichococcus) were enriched (from 9.83% to 68.91% in total). Ammonia nitrogen assimilating into Org-N and denitrification may be nitrogen pathways based on predict analysis. 29 ARGs were found with more co-occurrence patterns and high concentration of AZM (greater than 5 mg/L) caused their proliferation. Importantly, expect for some abundant taxa, rare taxa, potential pathogens and nitrogen-removal functional genera were the main potential hosts of ARGs.

Evaluating the effect of gradient applied voltages on antibiotic resistance genes proliferation and biogas production in anaerobic electrochemical membrane bioreactor

Anaerobic biological treatment technologies are one of the major hotspots of antibiotic resistance genes (ARGs). Previous studies have applied the electrochemical process to improve biogas production, however, it was challenged that high voltages might promote membrane permeability and reactive oxygen species overproduction to promote ARGs proliferation. Herein, the biogas production and ARGs proliferation in an anaerobic electrochemical membrane bioreactor (AnEMBR) were investigated at the gradient voltages of 0-0.9 V. Results show the reactor performances (average CH₄ production and current generation) were distinctly improved with the increase of applied voltage, and reached the optimum at 0.9 V. However, long-term application (>30 day) of 0.9 V deteriorated the reactor performances. Meanwhile, the relative abundances of most target ARGs in the supernatant and effluent of AnEMBR at 0.9 V increased by 0.68-1.55 and 0.42-1.26 logs compared to those before applying voltage, respectively. After disconnecting the circuit, these ARGs abundances all decreased to the original level. Significant correlations between intlI and ARGs (e.g., tetA, tetQ, sulI, and sulII) were observed, indicating horizontal gene transfer may contribute to the increased ARGs. Moreover, the shift of microbial communities caused by the applied voltage enriched potential ARGs-hosts (e.g., Tolumonas), contributing to the proliferation of ARGs.

Enhancing stability of aerobic granules by microbial selection pressure using height-adjustable influent strategy

Optimizing granules size distribution is critical for both reactor performance and stability. In this research, an optimal size range of 1800 to 3000 μm was proposed regarding mass transfer and granules stability based on granules developed at DO around 8.0 mg L^-1 with the feed COD:N:P at 100:5:1. A height-adjustable influent strategy was applied to facilitate the nutrient storage of granules at optimum size range via microbial selective pressure. Results suggested insufficient hydraulic shear stress led to overgrowth of granules size. High abundance of filamentous bacteria (Thiothrix sp.) was observed in oversized granules, which detached and affected the remaining granules, resulting in severe sludge bulking. Strong hydraulic shear stress suppressed uncontrolled growth of granules. However, fewer abundance of simultaneous nitrification and denitrification (SND) bacterium was acquired, which led to unfavored SND effect and total nitrogen (TN) removal efficiency. The height-adjustable influent strategy facilitated the poly-β-hydroxybutyrate (PHB) storage of granules at optimum size range, while limiting the overgrowth of granules size. Additionally, more than 87.51% of total granules situated in optimal sizes range, which led to higher abundance of SND bacterium and higher TN removal efficiency.

Responses of aerobic granular sludge to fluoroquinolones: Microbial community variations, and antibiotic resistance genes

In this study, aerobic granular sludge (AGS) was operated under high levels of ammonium for removing three fluoroquinolones (FQs), i.e., ciprofloxacin (CFX), ofloxacin (OFX), and norfloxacin (NFX) at 3, 300, and 900 µg/L, respectively. Two key objectives were to investigate the differential distribution of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in sludge fractions and to evaluate correlations between ARGs and MGEs to nitrifying and denitrifying bacteria. AGS showed excellent stability under the exposure of FQs, with nitrite-oxidizing bacteria (NOB) more sensitive to FQs than ammonium-oxidizing bacteria (AOB). Specific oxygen utilization rates (SOUR) showed a reduction of 26.9% for NOB but only 4.0% of the reduced activity of AOB by 3 μg/L FQs. AGS performed better removal efficiencies for CFX and NFX than OFX, and the efficiencies increased with their elevated concentrations, except at 900 μg/L FQs. The elevated FQ concentrations led to a significant enrichment of intI1 and genus Thauera, while qnrD and qnrS showed no accumulation. Compared to nitrifiers, FQs relevant ARGs and the intI1 gene preferred to exist in denitrifiers, and the abundance of denitrifiers behaved a decreasing trend with the sludge size. Two quinoline-degrading bacteria were found in the AGS system, i.e., Alicycliphilus and Brevundimonas, possibly carrying qnrS and qnrD, respectively. Their relative abundance increased with the sludge size, which was 2.18% in sludge <0.5 mm and increased to 3.70% in sludge >2.0 mm, suggesting that the AGS may be a good choice in treating FQs-containing wastewater.

Tetracyclines in the environment: An overview on the occurrence, fate, toxicity, detection, removal methods, and sludge management

Tetracyclines (TCs) are a group of broad-spectrum antibiotics having vast human, veterinary, and aquaculture applications. The continuous release of TCs residues into the environment and the inadequate removal through the conventional treatment systems result in its prevalent occurrence in soil, surface water, groundwater, and even in drinking water. As aqueous TCs contamination is the tip of the iceberg, and TCs possess good sorption capacity towards soil, sediments, sludge, and manure, it is insufficient to rely on the sorptive removal in the conventional water treatment plants. The severity of the TCs contamination is evident from the emergence of TCs resistance in a wide variety of microorganisms. This paper reviews the recent research on the TCs occurrence in the environmental matrices, fate in natural systems, toxic effects, and the removal methods. The high performance liquid chromatography (HPLC) determination of TCs in environmental samples and the associated technology developments are analyzed. The benefits and limitations of biochemical and physicochemical removal processes are also discussed. This work draws attention to the inevitability of proper TC sludge management. This paper also gives insight into the limitations of TCs related research and the future scope of research in environmental contamination by TCs residues.

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.

A nanofluidic device for ultrasensitive and label-free detection of tetracycline in association with γ-cyclodextrin and GO

Herein, an ultrasensitive and selective nanofluidic device for tetracycline (TC) was developed in association with γ-cyclodextrin and graphene oxide (GO). The assay was designed based on the change of the nanochannel surface charge due to the selective recognition ability of GO between aptamers and TC-aptamer complexes. And γ-cyclodextrin was utilized to eliminate the excess TC since the amine group molecules were inclined to be adsorbed onto the nanochannel surface and affected the adsorption efficiency of the nanochannel. In the presence of TC, TC specifically binded to the aptamer to form TC-aptamer and was separated from GO. The TC-aptamer complexes could be quantitated with conical nanochannels coated with polyethyleneimine (PEI)/Zr4+. The redundant TC was removed by γ-cyclodextrin. The detection limit of the nanofluidic device was as low as 2 ng L-1 (S/N = 3) and the linear range was 10 ng L-1 to 10 μg L-1. Moreover, the nanofluidic device provided high specificity and good recovery rates of 94.8-109.3% in natural river, tapwater and wastewater samples. The results revealed that our study provided a new rapid detection method for trace contaminant analysis.

Tetracycline-Resistant Bacteria Selected from Water and Zebrafish after Antibiotic Exposure

The emergence of antibiotic-resistant pathogens due to worldwide antibiotic use is raising concern in several settings, including aquaculture. In this work, the selection of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) was evaluated after exposure of zebrafish to oxytetracycline (OTC) for two months, followed by a recovery period. The selection of ARB in water and fish was determined using selective media. The abundance of tetA genes was estimated through qPCR. Higher prevalence of ARB was measured in all samples exposed to the antibiotic when compared to control samples, although statistical significance was only achieved five days after exposure. Isolates recovered from samples exposed to the antibiotic were affiliated with Pseudomonas and Stenotrophomonas. Various antibiotic susceptibility profiles were detected and 37% of the isolates displayed multidrug resistance (MDR). The selection of the tetA gene was confirmed by qPCR at the highest OTC concentration tested. Two MDR isolates, tested using zebrafish embryos, caused significant mortality, indicating a potential impact on fish health and survival. Overall, our work highlights the potential impact of antibiotic contamination in the selection of potential pathogenic ARB and ARGS.

Removal of Tetracycline Oxidation Products in the Nanofiltration Process

The possibility of removing tetracycline (TRC) from water in an integrated advanced oxidation and membrane filtration process was investigated. Ozonation and UV/H2O2 photooxidation were applied for the destruction of TRC. Six oxidation products (OPs) retaining the structural core of TRC have been identified. One new TRC oxidation product, not reported so far in the literature, was identified—ethyl 4-ethoxybenzoate. All identified OPs were effectively retained on the membrane in the nanofiltration process. However, chemical oxygen demand (COD) measurements of the filtrates showed that in the case of UV/H2O2 oxidation, the OPs passed through the membrane into the filtrate. Various water matrices were used in the research, including the river water untreated and after ozone treatment. It has been shown that organic matter present in surface water can improve pharmaceutical retention, although it contributes to significant membrane fouling. Pre-ozonation of the river water reduced the membrane fouling. The XPS analysis was used to show ozone and H2O2 influence on the top polymer layer of the membrane. It was shown that the oxidants can damage the amide bond of the polyamide.

Granulation enhancement and microbial community shift of tylosin-tolerant aerobic granular sludge on the treatment of tylosin wastewater

To reduce the environment pollution from the extensive use of tylosin (TYL), in this study, an antibiotic adaptive strategy was used to enhance the TYL tolerance of aerobic granular sludge (AGS) for the treatment of TYL wastewater. The results showed that the granulation process was enhanced after 30 days of operation. The TYL-tolerant AGS gradually formed and maintained a diameter of 1.2 mm, with the mixed liquor suspended solids (MLSS) of 6810 mg⋅L^-1 and sludge volume index (SVI) of 26 mL⋅g^-1. Meanwhile, the chemical oxygen demand (COD), NH₄⁺-N, and total N removal effiencies could reach up to 92.9%, 91.7%, 88.5%, respectively. The average TYL removal rate was 85.5% with the effuent TYL of 1.45 mg⋅L^-1. In addition, the microbial communities shifted significantly that Bacteroidetes and Proteobacteria dominated the phylm, and the Macellibacteroides was the major genus which might possess the anitibiotic resistance genes of TYL.

Fate of integrons, antibiotic resistance genes and associated microbial community in food waste and its large-scale biotreatment systems

The prevalence and dissemination of antibiotic resistance genes (ARGs) have been globally gained increasing concerns. However, the fate and spread of ARGs in food waste (FW) and its large-scale biotreatment systems are seldomly understood. Here, we investigated the initial and biologically treated FW in two major FW treatment systems of aerobic fermentation (AF) and anaerobic co-digestion (AcoD) processes. The total relative abundances of integrons and ARGs significantly increased from initial FW to treated FW. Among targeted ARGs, ermB and strB were predominant ARGs, which accounted for 52.58-95.28% of total abundance across all samples. Mantel test indicated that integrons (intl1 and intl2) were positively and significantly correlated with detected ARGs (Mantel test, r = 0.24, p < 0.05), suggesting integrons display significant contributions on driving ARG alteration during FW treatment processes. RDA results indicated that bla_OXA, strB and bla_TEM were more likely to be proliferated by potential host of Firmicutes (96.55-99.77%) in initial FW, while bla_CTX-M and mefA were potentially enriched by Proteobacteria (17.12-49.82%) in AF system and ermB, sul1, aadA and tetQ were possibly enhanced by Bacteroidetes (27.43-43.71%) in AcoD system. Consideration of the higher enriched abundance of total ARGs (66.88 ± 87.34 times) and the used inoculum sludge in AcoD-treated system, the resource utilization of anaerobically digested products should draw our more attentions. These findings would deepen our understanding of prevalence and proliferation of ARGs in FW treatment systems and serve as a foundation for guiding the application of biologically treated FW.

Deciphering pollutants removal mechanisms and genetic responses to ampicillin stress in simultaneous heterotrophic nitrification and aerobic denitrification (SHNAD) process treating seawater-based wastewater

Pollutants removal and genetic responses of simultaneous heterotrophic nitrification and aerobic denitrification (SHNAD) treating seawater-based wastewater were studied under ampicillin stress. Marine SHAND bacteria exhibited good tolerance to 10 mg/L ampicillin with nitrogen removal efficiency and organics removal efficiency of 94.5% and 82.6%, respectively. Besides, the half-inhibitory concentration of ampicillin on marine SHAND bacteria was 50 mg/L. The relative abundances of antibiotic resistance genes (ARGs) first decreased and then increased with ampicillin addition. The blaVIM played an important role to resist 25 mg/L ampicillin, which contributed to the recovery of pollutants removal. BlaSHV and blaTEM dominated ARG subtypes, which accounted for 96.6% of ARGs abundance. At 50 mg/L ampicillin, reactive oxygen species (ROS) production and cell numbers of apoptosis increased by 47.9% and 367.5%, respectively. The overproduction of ROS was stimulated by ampicillin, which caused bacterial cell apoptosis. Marine SHNAD bacteria produced more extracellular polymeric substances to resist ampicillin.

Isolation of oxytetracycline-degrading bacteria and its application in improving the removal performance of aerobic granular sludge

Aerobic granular sludge (AGS) is a type of biofilm with good sedimentation and density, high biomass, high organic load tolerance and toxicity resistance. Oxytetracycline (OTC) is an antibiotic widely used in livestock and aquaculture, and its low absorption and high residue bring many risks and harms to the ecological environment. In this study, an OTC-degrading strain TJ3 was isolated from AGS and identified as Pandoraea sp. The biodegradation characteristics of OTC by strain TJ3 under different environmental conditions were also investigated. The results showed that the optimal initial pH value and temperature for the culture strain were 6.0 and 30 °C, respectively. At an inoculation dose of 6% (v/v), the removal rate of OTC by strain TJ3 was remarkable (59.4%). Furthermore, when the sodium acetate was present as an additional substrate, the biomass and the OTC removal rate of strain TJ3 were improved. The biodegradability of strain TJ3 to OTC was proved by LC-QTOF/MS, and two possible biotransformation products, i.e. m/z 416 and 219, were identified. In the bioaugmentation experiments of AGS by strain TJ3, the average OTC removal rate was 92.89% after the stable operation of bioreactor. The chemical oxygen demand (COD), ammonium nitrogen (NH₄⁺-N) and total phosphorus (TP) were efficiently removed. The microbial community structure had significantly changed at the genus level, and the relative abundance of Zoogloea, Pandoraea, Cloacibacterium and Desulfovibrio increased evidently. These results implied that the OTC removal performance and the structural stability of AGS were improved. In this study, Pandoraea sp. TJ3 was applied to removal OTC for the first time, and results showed that Pandoraea sp. TJ3 may be a new auxiliary bacterial resource for the biodegradation of OTC and a potential candidate in the treatment of antibiotic wastewater.

Enhanced performance of tetracycline treatment in wastewater using aerobic granular sludge with in-situ generated biogenic manganese oxides

Wastewaters containing tetracycline (TC) are produced in many industries, and biotechnology is an economic way to treat it. In this work, aerobic granular sludge (AGS) modified with in-situ generated biogenic manganese oxides (BioMnOx), named after manganese-oxidizing AGS (Mn-AGS), was used to treat TC in wastewater. Comparisons between Mn-AGS and AGS indicated that Mn-AGS showed superior TC resistance and treatment results than AGS. The activity of Mn-AGS was not inhibited by TC content as high as 20 mg/L. Wastewater TC could be removed stably and efficiently (95.2 ± 0.8%) in the Mn-AGS reactors after 119 days' acclimation. Furthermore, TC may be first adsorbed on Mn-AGS sludge and then degraded by both microbial community and BioMnOx. TC adsorption could be greatly improved by increasing solution pH, which can be attributed to the increase in negatively charged TC species at high pHs. The microbial community changed greatly after TC exposure and some TC-resistant bacteria, such as Flavobacterium, were enriched in the final sludge. Moreover, the antibiotic resistance genes (ARGs) tetA, tetG, and tetX largely increased and the microorganisms were TC-resistant through efflux pumps and antibiotic inactivation mechanisms. This work suggests a new biological-chemical coupling strategy, Mn-AGS, to treat antibiotics in organic wastewater with high efficiency and stability.

Long-term responses of antibiotic resistance genes under high concentration of enrofloxacin, sulfadiazine and triclosan in aerobic granular sludge system

It is worth to reveal the long-term responses of antibiotic resistance genes (ARGs) in aerobic granular sludge (AGS) system exposed to high level enrofloxacin (ENR), sulfadiazine (SDZ) and triclosan (TCS). In present study, ppm level ENR, SDZ and TCS were added into three AGS reactors, respectively. ARGs in ENR and SDZ systems showed trends of increasing first and then decreasing, which were contrary to that in TCS system. 80%, 56% and 40% ARGs in ENR, SDZ and TCS systems, respectively, were enriched after loading, but several ARGs still kept high enrichment values after the withdrawn of loadings. The dominant bacteria in ENR (Flavobacterium), SDZ (Candidatus_Competibacter and Defluviicoccus) and TCS (Defluviicoccus) systems might contribute to the reductions of ARGs. IntI1 altered the overall ARGs profiles through horizontal gene transfer. The interactions of bacterial communities and environmental factors might be responsible for the different ARGs patterns in ENR, SDZ and TCS systems.

Microbial degradation of tetracycline in the aquatic environment: a review

Tetracycline residues have frequently been detected in multi-environmental media, and it could induce antibiotic resistance genes (ARGs) in microorganisms, which has attracted great attention. Where biodegradation processes may be a promising strategy to remove tetracycline. Thus, this study mainly considers: (i) the degradation of tetracycline by microorganisms including single microorganisms and microbial flora; (ii) the elimination of tetracycline during biochemical treatment processes and advanced treatment systems in wastewater treatment plants (WWTPs) and constructed wetlands (CWs); (iii) the degradation of tetracycline by biological coupling processes; (iv) the confusion and problem of tetracycline biodegradation. Furthermore, the characteristics and comparison of tetracycline biodegradation have been discussed in detail. Additionally, future research directions are suggested to reduce tetracycline in the aquatic environment, especially tetracycline biodegradation and the nitrogen conversion process. Highlights Degradation of tetracycline by pure culture strains and microflora was significant. Degradation of tetracycline by biochemical treatment process was summarized. Advanced treatment process in CWs could eliminate tetracycline. Future research directions on biodegradation of tetracycline are proposed.

Response of denitrifying community, denitrification genes and antibiotic resistance genes to oxytetracycline stress in polycaprolactone supported solid-phase denitrification reactor

The coexistence of nitrate and antibiotics in wastewater is a common problem. The study aimed to explore the response of denitrifying community, denitrification genes and antibiotic resistance genes (ARGs) to oxytetracycline (OTC) stress in polycaprolactone (PCL) supported solid-phase denitrification (SPD) reactors. Complete nitrate reduction (greater than99%) was achieved in SPD system with OTC stress of 0, 0.05, 0.25 and 1 mg L^-1 during three-month operation, while it significantly declined by about 5% at a further increased OTC level of 5 mg L^-1. The efficient denitrification strongly related with a rich diversity of denitrifiers, while the abundances of which dramatically reduced as the OTC concentration reached ≥0.25 mg L^-1, which caused significant decline of denitrification genes, especially for narH, narJ, narI nirD, nosZ, and norB. Tetracycline resistance genes were a major type of promoted ARGs by different OTC stress, mainly related with the increase of tet36, tetG, tetA, tetM and tetC.

Effects of exposure to polyether sulfone microplastic on the nitrifying process and microbial community structure in aerobic granular sludge

The effects of polyether sulfone (PES) microplastic concentration on the nitrifying process of aerobic granular sludge (AGS) were investigated together with the microbial community structure of AGS. The PES microplastic concentration inhibited the removal of ammonia nitrogen only to a small extent. The average total nitrogen removal rate increased by 5.6% after PES addition. On the 30th day, the addition of 0.5 g/L PES inhibited the specific nitrate reduction rate (SNRR) by 38.84 mg N/(g MLSS·h). Nitrite oxidase (NOR) performance of the AGS were inhibited with addition the PES. According to the high-throughput sequencing results, in the presence of PES, the abundance of Bacillales_Incertae Sedis XII reduced, while the abundance of Anaerolineaceaen increased in the AGS. According to the clusters of orthologous groups (COG) and kyoto encyclopedia of genes and genomes (KEGG), the content of cytochrome c-containing reduced and the Amino Acid Metabolism increased with addition 0.5 g/L PES microplastic.

A global environmental health perspective and optimisation of stress

The phrase "what doesn't kill us makes us stronger" suggests the possibility that living systems have evolved a spectrum of adaptive mechanisms resulting in a biological stress response strategy that enhances resilience in a targeted quantifiable manner for amplitude and duration. If so, what are its evolutionary foundations and impact on biological diversity? Substantial research demonstrates that numerous agents enhance biological performance and resilience at low doses in a manner described by the hormetic dose response, being inhibitory and/or harmful at higher doses. This Review assesses how environmental changes impact the spectrum and intensity of biological stresses, how they affect health, and how such knowledge may improve strategies in confronting global environmental change.

Profiles of ARGs and their relationships with antibiotics, metals and environmental parameters in vertical sediment layers of three lakes in China

Antibiotic resistance is a global health problem, and the role of antibiotics and metal pollution in antibiotic resistance in sediment biocenosis is limited. The occurrence and relationship between antibiotic resistance genes (ARGs), antibiotics, metals and environmental parameters were investigated in vertical layers of sediments in rural and urban lakes. Generally, the total concentrations of seven antibiotics were significantly higher in the rural lake (Lake Taihu = 96%) than in the urban lakes (Xuanwu = 0.3%, Wulongtan = 3%), while similar concentrations were observed for metals (Taihu (34%), Xuanwu (33%) and Wulongtan (33%)). The concentration of metals and antibiotics were mostly higher in the surface sediment layers than the deeper ones (for antibiotics; surface layers = 89%, deeper layer = 11%, for metals; surface = 65%, deep = 35%). The ARGs showed no significant difference between surface and deeper sediments (surface = 48%, deep = 52%, p < 0.05). The potential ecological risk index of Ni, Cu, Zn, Cr, Mn, As, Cd, and Pb contamination showed that Lake Taihu and Wulongtan had moderate ecological risks while Lake Xuanwu had a low ecological risk. Pearson coefficient and network analysis showed that direct and indirect relationship existed among antibiotics, metals, environmental parameters, and ARGs, and the relationship was linked by key environmental components. tetA, bla_TEM, SDZ, TOC, OFL, Cd, OTC, NOR, Ni, sulA, AUR, TC, DOX and TN were the major factors that influence the distribution of resistance genes, forming a complex network mechanism of antibiotic resistance. Our study revealed that antibiotics and heavy metals are widely distributed in the surficial sediments and the proliferation of ARGs are influenced by some key environmental components.

Impacts of typical pharmaceuticals and personal care products on the performance and microbial community of a sponge-based moving bed biofilm reactor

Four lab-scale moving bed biofilm reactors (MBBRs) were built to treat simulated wastewater containing typical pharmaceuticals and personal care products (PPCPs). The efficiency in removing different PPCPs at different concentrations (1, 2 and 5 mg/L) and their effects on the performance of MBBRs were investigated. Results showed that the average removal efficiencies of sulfadiazine, ibuprofen and carbamazepine were 61.1 ± 8.8%, 74.9 ± 8.8% and 28.3 ± 7.4%, respectively. Compared to the reactor without PPCPs, the total nitrogen (TN) removal efficiency of the reactors containing sulfadiazine, ibuprofen and carbamazepine declined by 21%, 30% and 42%, respectively. Based on the microbial community analysis, increasing the PPCPs concentration within a certain range (<2 mg/L) could stimulate microbial growth and increase microbial diversity yet the diversity reduced when the concentration (5 mg/L) exceeded the tolerance of microorganisms. Furthermore the presence and degradation of different PPCPs resulted in a different kind of microbial community structure in the MBBRs.