Distinguishing effects of ultraviolet exposure and chlorination on the horizontal transfer of antibiotic resistance genes in municipal wastewater

Sodium citrate enhances anaerobic fermentation of granular sludge: the multifaceted roles of structure disruption and metabolic regulation

Anaerobic fermentation is an efficient approach for recovering organic carbon and other valuable resources from waste sludge, yet its efficiency is constrained by the structural stability of extracellular polymeric substances (EPS), especially for aerobic granular sludge (AGS). Despite the abundant physical-chemical pre-treatment approaches for enhancing EPS dissolution, biocompatible strategies coordinating structural disruption with metabolic regulation remain unexplored. Herein, sodium citrate (SC) was used to enhance the performance of anaerobic fermentation of AGS. The results suggested that SC significantly enhanced the hydrolysis efficiency and volatile fatty acids (VFAs) production of AGS. Despite the direct conversion of SC to acetate, indirect enhancement played more important roles in AGS fermentation. Mechanism analysis indicated that SC disrupted granular sludge structure by chelating Ca2+ and facilitated the release of EPS and hydrolytic enzymes, which was conducive to sludge hydrolysis and acidification. At the level of microbial community, SC facilitated the accumulation of VFAs by enriching the acid-producing microorganisms and inhibiting the acid-consuming microorganisms. Furthermore, SC regulated the genes involved in the direct generation of acetate and pyruvate-centric metabolism, resulting in the massive accumulation of VFAs. Finally, the economic benefits resulting from increased VFA production versus SC costs. Overall, SC enhanced the anaerobic fermentation of AGS by simultaneously affecting EPS structure and regulating metabolism, and this study provided efficient methods for AGS anaerobic treatment.

The overlooked risk of horizontal transfer of plasmid-borne antibiotic resistance genes induced by synthetic phenolic antioxidants

Plasmid-borne conjugation transfer of antibiotic resistance genes (ARGs) triggered by non-antibiotic stresses has attracted widespread attention, known to motivate conjugation through well-recognized reactive oxygen species and SOS response. However, a notable knowledge gap remains on the potential risks of reductive compounds, such as synthetic phenolic antioxidants (SPAs), in facilitating horizontal gene transfer by the other mechanisms beyond intracellular ROS. Therefore, intragenus and wastewater indigenous microbiota conjugation models were established to examine conjugative transfer frequency of RP4 plasmid under exposure of four extensively detected SPAs. The mechanisms were elucidated utilizing fluorescence detection, RT-qPCR, and transcriptomic analysis with 3-tert-butyl-4-hydroxyanisole (BHA) serving as a representative SPA. Results demonstrated that conjugation transfer frequencies of both models were significantly promoted without triggering SOS responses under exposure to high doses of BHA. Furthermore, BHA exposure benefited conjugation progress through improving membrane permeability of donors and ameliorating cellular energy supply. In addition, BHA exposure activated the RP4-encoded transfer apparatus by regulating the expression of associated genes. This study highlighted and provided a stark reminder about the potential horizontal gene transfer risks posed by SPAs exposure, which were regarded as a neglected driver in the dissemination of ARGs.

Chlorination-induced spread of antibiotic resistance genes in drinking water systems

Chlorine, the most widely utilized disinfectant for drinking water globally, has recently been implicated in facilitating the spread of antibiotic resistance genes (ARGs), raising concerns about its underestimated environmental and ecological risks. However, given the current fragmented research focus and results, a comprehensive understanding of the potential mechanisms and influencing factors behind chlorination-promoted ARGs transmission in drinking water systems is crucial. This work is the first to systematically review the variations in abundance, transmission mechanisms, influencing factors, and mitigation strategies related to ARGs during the chlorination process. The results indicated that chlorination could induce genetic mutations and promote horizontal gene transfer through multiple pathways, including increased reactive oxygen species, enhanced membrane permeability, stimulation of the SOS response, and activation of efflux pumps. In addition, this work delves into significant discoveries regarding the factors affecting ARG transmission in drinking water, such as chlorine concentration, reaction time, disinfection byproducts, pipe materials, biofilms, and the water matrix. A series of effective strategies from water source to point-of-use were proposed aimed at mitigating ARGs transmission risks in the drinking water system. Finally, we address existing challenges and outline future research directions to overcome these bottlenecks. Overall, this review aims to advance our understanding of the role of chlorination in the dissemination of ARGs and to inspire innovative research ideas for optimizing disinfection techniques, minimizing the risks of antibiotic resistance transmission, and enhancing the safety of drinking water.

The fate of intracellular and extracellular antibiotic resistance genes during ultrafiltration-ultraviolet-chlorination in a full-scale wastewater treatment plant

Effluent from wastewater treatment plants (WWTPs) is recognized as a significant source of antibiotic resistance genes (ARGs) in the environment. Advanced treatment processes such as ultrafiltration (UF), ultraviolet (UV) light disinfection, and chlorination have emerged as promising approaches for ARG removal. However, the efficacy of sequential disinfection processes, such as UF-UV-chlorination on intracellular (iARGs) and extracellular ARGs (eARGs), remains largely unknown. This study investigates the impact of this sequential disinfection process on the fate of iARGs, eARGs, and a crucial mobile genetic element (intI1) within a full-scale WWTP. Our findings revealed that the UF-UV-chlorination process effectively reduced the overall absolute abundance of detected ARGs in the effluent by 1.93 log, and intI1 by 0.86 log, compared to secondary effluent. The majority of these removals was achieved due to the UF and UV disinfection, while chlorination showed negligible impact on the absolute abundance of ARGs in the final effluent. Notably, five genera were identified as potential hosts for intI1 and eight iARGs, including aac(6')-Ib-cr, drfA1, sul1, sul2, ermB, mefA, tetA, and tetX, suggesting a high potential for horizontal gene transfer involving these ARGs. Overall, this study demonstrated that UF-UV-chlorination is a highly effective method for reducing ARGs in effluent from WWTPs.

Impact of low-dose free chlorine on the conjugative transfer of antibiotic resistance genes in wastewater effluents: Identifying key environmental factors for predictive modeling

Reclaimed water disinfection results in the coexistence of antibiotic resistance genes (ARGs) and low-dose free chlorine in receiving environments. However, the impact of low-dose free chlorine on ARGs conjugative transfer and the key factors influencing the transfer under complex environmental conditions remain unclear, hindering the establishment of an effective monitoring system for resistance pollution in reclaimed water. This study investigated ARGs conjugative transfer under the influence of free chlorine at environmentally relevant concentrations and key interactive factors using machine learning models. The results showed that low-dose free chlorine (0.05-0.3 mg/L) promoted ARGs conjugative transfer, with 0.15 mg/L having a greater promoting effect than free chlorine concentrations of 0.05 and 0.3 mg/L. Additionally, different exposure patterns of low-dose chlorine affected ARGs conjugative transfer, with intermittent exposure posing a higher risk of ARGs dissemination. SVM linear model performed best in predicting ARGs conjugative transfer (RMSE=0.012, R2=0.975), and the SHapley Additive Explanations (SHAP) method revealed that key factors such as HCO3-, SAA, NO3-, and HA had positive SHAP values, indicating a positive influence on ARGs transfer under low-dose chlorine, making them the key features for predicting the ARGs conjugative transfer under the low-dose chlorine exposure. This study also revealed potential mechanisms of ARGs transfer under continuous low-dose free chlorine exposure, including intracellular reactive oxygen species (ROS), enzyme activity, cell membrane permeability, and gene expression. The integration of the machine learning model and post-hoc interpretation methods clarified the key drivers of ARGs conjugative transfer in reclaimed water-replenished environments, providing new insights for the safe reuse of reclaimed water and the development of river monitoring indicators.

Antihistamine drug loratadine at environmentally relevant concentrations promotes conjugative transfer of antibiotic resistance genes: Coeffect of oxidative stress and ion transport

Due to the widespread use of loratadine (LOR) as an antihistamine, it is widely distributed in the environment as an emerging contaminant. However, its impact on the dissemination of antibiotic resistance genes (ARGs) remains unclear. This study investigated the effect of LOR on the conjugative transfer of ARGs and elucidated the potential mechanisms through transcriptome analysis. The results showed that LOR significantly promoted the frequency of conjugative transfer up to 1.5- to 8.6-fold higher compared with the control group. Exposure to LOR increased reactive oxidative species (ROS) and intracellular Ca2+ concentrations, leading to the upregulation of expression of genes related to transmembrane transport and SOS response. Meanwhile, it stimulated the increase of cell membrane permeability. Moreover, LOR exposure could enhance H+ efflux in donor bacteria, resulting in the decrease of intracellular pH and the elevation of transmembrane potential, which could induce the increase of ion transport, thereby promoting plasmid efflux from the cell membrane. Based on this, we inferred that LOR can induce an increase in ROS level and intracellular Ca2+ concentrations, and promoted the efflux of intracellular H+. This, in turn, triggered the intensification of various ion transport processes on the cell membrane, thereby increasing membrane permeability and accelerating plasmid efflux. Ultimately, the coeffect of oxidative stress response and ion transport promoted conjugative transfer. This study demonstrated that LOR significantly promotes plasmid-mediated conjugative transfer of ARGs, providing novel insights into the mechanisms underlying this process.

Effect of non-antibiotic factors on conjugative transfer of antibiotic resistance genes in aquaculture water

Aquaculture water with antibiotic resistance genes (ARGs) is escalating due to the horizontal gene transfer. Non-antibiotic stressors specifically found, including those from fishery feed and disinfectants, are potential co-selectors. However, the mechanisms underlying this process remains unclear. Intragenus and intergenus conjugative transfer systems of the antibiotic-resistant plasmid RP4 were established to examine conjugative transfer frequency under exposure to five widely used non-antibiotic factors in aquaculture water: iodine, oxolinic acid, NO2-N, NO3-N and H2O2 and four different recipient bacteria: E. coli HB101, Citrobacter portucalensis SG1, Vibrio harveyi and Vibrio alginolyticus. The study found that low concentrations of non-antibiotic factors significantly promoted conjugative transfer, whereas high concentrations inhibited it. Moreover, the conjugation transfer efficiencies were significantly different with different bacterial species within (E. coli HB101 ∼ 10-3 %) or cross genera (C. portucalensis SG1 ∼10-5 %, V. harveyi ∼1 %). Besides, excessive exposure concentrations inhibited the expression of related genes and the generation of reactive oxygen species (ROS). Regulation of multiple related genes and ROS-induced SOS responses are common primary mechanisms. However, the mechanisms of non-antibiotic factors differ from those of standard antibiotics, with direct changes in cell membrane permeability potentially playing a dominant role. Additionally, variations among non-antibiotic factors and the specific characteristics of bacterial species contribute to differences in conjugation mechanisms. Notably, this study found that non-antibiotic factors could increase the frequency of intergeneric conjugation beyond that of intrageneric conjugation. Furthermore, non-antibiotic factors influenced by multiple transport systems may raise the risk of unintended cross-resistance, significantly amplifying the potential for resistance gene spread. This study underscores the significance of non-antibiotic factors in the propagation of ARGs, highlighting their role in advancing aquaculture development and protecting human health.

High temperatures promote antibiotic resistance genes conjugative transfer under residual chlorine: Mechanisms and risks

The impact of residual chlorine on the dissemination of antibiotic resistance during the distribution and storage of water has become a critical concern. However, the influence of rising temperatures attributed to global warming on this process remains ambiguous, warranting further investigation. This study investigated the effects of different temperatures (17, 27, 37, and 42°C) on the conjugative transfer of antibiotic resistance genes (ARGs) under residual chlorine (0, 0.1, 0.3, and 0.5 mg/L). The results indicated that high temperatures significantly increased the conjugative transfer frequency of ARGs in intra-species under residual chlorine. Compared to 17°C, the transfer frequencies at 27°C, 37°C, and 42°C increased by 1.07-2.43, 1.20-4.80, and 1.24-2.82 times, respectively. The promoting effect of high temperatures was mainly due to the generation of reactive oxygen species, the triggered SOS response, and the formation of pilus channels. Transcriptomic analysis demonstrated that higher temperature stimulates the electron transport chain, thereby enhancing ATP production and facilitating the processes of conjugative, as confirmed by inhibitor validation. Additionally, rising temperatures similarly promoted the frequency of conjugative transfer in inter-species and communities under residual chlorine. These further highlighted the risk of antibiotic resistance spread in extreme and prolonged high-temperature events. The increased risk of antibiotic resistance in the process of drinking water transmission under the background of climate warming is emphasized.

Effects of UVC doses on the removal of antimicrobial resistance elements from secondary treated sewage

Wastewater treatment plants (WWTPs) currently face major challenges toward the removal of microcontaminants and/or microbial matrices and consequently play an important role in the potential dissemination of biological resistance in freshwater. The ultraviolet (UV) system is a tertiary treatment strategy increasingly applied worldwide, although many studies have shown that disinfected effluent can still contain antibiotic-resistant bacteria and resistance genes. Therefore, to better understand the effects of UV radiation doses on the removal of all resistance elements (antibiotics, antibiotic-resistant bacteria, and antibiotic resistance genes), the present study was designed using a pilot-scale photoreactor. The UV doses could be varied to investigate whether there is an optimal UV dose capable of removing all resistance elements and also if the UV dose frequently applied in full-scale systems is able to reduce the resistance elements. The effect of different UV doses (A, 0-10 mJ/cm2; B, 10-15 mJ/cm2; and C, > 15 mJ/cm2) in a pilot-scale photoreactor on the removal of antibiotics, antibiotic-resistant bacteria, and genes from the effluent of a UASB reactor followed by a biological trickling filter system (UASB-TF) fed with real sanitary sewage was investigated. Samples of influent and effluent from the UVC photoreactor were collected, and the concentration levels of norfloxacin (NOR), ciprofloxacin (CIP), and levofloxacin (LEV) were assessed. The qnrB, sul1, ermB, integron-integrase (intI1), and 16S rRNA genes, total heterotrophic bacteria (THB), and bacterial resistance to azithromycin and sulfamethoxazole were also investigated. Results indicated that LEV and intI1 were found in the highest median concentrations in the photoreactor influent. Although most antibiotics (NOR and CIP) and ARGs (intI1, 16S rRNA, and qnrB) were apparently better removed with the highest UV dose (> 15 mJ/cm2) applied, except for LEV, sul1, and ermB genes, the Kruskal-Wallis test reported no significant difference between low and high doses. ARB removal (from 80 to 100%) was observed at all UV doses. Principal component analysis (PCA) suggested a clear pattern of pollutant groups, i.e., antibiotics, ARG, and ARB, which exhibited low (median of 8-16%), medium (37-96%), and high (> 97%) removal percentages, respectively. These results demonstrated that UVC photoreactors can be an alternative to complement biological treatment in sewage treatment plants at the dose normally applied in full-scale WWTPs (> 15 mJ/cm2). However, there was no optimal single dose capable of removing all the resistance elements investigated.

Microplastics Exacerbated Conjugative Transfer of Antibiotic Resistance Genes during Ultraviolet Disinfection: Highlighting Difference between Conventional and Biodegradable Ones

Microplastics (MPs) have been confirmed as a hotspot for antibiotic resistance genes (ARGs) in wastewater. However, the impact of MPs on the transfer of ARGs in wastewater treatment remains unclear. This study investigated the roles and mechanisms of conventional (polystyrene, PS) and biodegradable (polylactic acid, PLA) MPs in the conjugative transfer of ARGs during ultraviolet disinfection. The results showed that MPs significantly facilitated the conjugative transfer of ARGs compared with individual ultraviolet disinfection, and PSMPs exhibited higher facilitation than PLAMPs. The facilitation effects were attributed to light shielding and the production of reactive oxygen species (ROS) and nanoplastics from ultraviolet irradiation of MPs. The light shielding of MPs protected the bacteria and ARGs from ultraviolet inactivation. More importantly, ROS and nanoplastics generated from irradiated MPs induced intracellular oxidative stress on bacteria and further increased the cell membrane permeability and intercellular contact, ultimately enhancing the ARG exchange. The greater fragmentation of PSMPs than PLAMPs resulted in a higher intracellular oxidative stress and a stronger enhancement. This study highlights the concerns of conventional and biodegradable MPs associated with the transfer of ARGs during wastewater treatment, which provides new insights into the combined risks of MPs and ARGs in the environment.

Critical evaluation of extracellular polymeric substances extraction methods: Extraction efficiency, molecular characteristics, and heavy metals binding properties

Extracellular polymeric substances (EPS) significantly influence the properties and performance of waste activated sludge. Various pretreatment protocols with different extraction efficiency and characteristics of EPS have been reported, which markedly impact subsequent treatment and disposal of sewage sludge. This study systematically assesses the EPS properties from twelve extraction pretreatment methods. The organic and inorganic matters content, cell lysis, basic physicochemical property, molecular weight distribution, and fluorescence properties of extracted EPS were determined. Physical extraction methods (Centrifugation, Heat, and Ultrasound) were relatively mild, resulting in lower extraction of organic matter contents from EPS (< 6 mg total organic carbon /g volatile solids). Biological extraction methods (Enzyme and Enzyme-NaOH) exhibited high EPS extraction efficiency however led to significant cell lysis, thereby contaminating the extracted EPS with intracellular substances. In addition, heating and biological extraction methods excessively degraded EPS, resulting in a large amount of small molecular weight matters (≤ 103 Da) generation. Chemical extraction methods offered efficient EPS extraction with the different degrees of cell lysis, but it would introduce chemical reagent residues in EPS. Among those extraction methods, EPS extracted by cation exchange resin (CER) method had uniform and abundant molecular weight matters and fluorescence matters distribution. After dialysis, the residual Na and other metal elements could be significantly removed. Then, the fluorescence quenching effect of Cu(II) and Zn(II) at 400 μM on the Bound-EPS after dialysis increased up to the maximum value of 65 % and 30 %, respectively, compared to that without dialysis. It indicates that dialysis coupled with CER extracted EPS has a well extraction efficiency and can maintain the original state of EPS for the subsequent investigation.

Degradation of extracellular antibiotic resistance gene through singlet oxygen produced by carbon nanotubes-activated persulfate

Extracellular antibiotic resistance gene (eARG) has emerged as a global crisis in recent years, yet commonly used disinfectants have proven ineffective for their elimination. Seeking to enhance the degradation efficiency of eARG, this study explored the potential of carbon nanotubes-activated persulfate (CNTs + PS) system as a novel method for eradicating eARG. Our findings demonstrated that CNTs + PS effectively disrupted the intact structure of eARG, inhibited their genetic replication and horizontal transfer capability, achieving remarkable degradation of eARG contamination. Further experiments revealed that 1O2 played a predominant role in eARG degradation, while electron transfer played minor roles in the degradation process. The carbonyl groups served as the primary sites for activating PS to generate 1O2. CNTs can enhance the efficiency of electron transfer from eARG to PS. Moreover, the degradation efficacy of eARG by CNTs + PS was influenced by various factors including the dosage ratio between CNTs and PS, initial concentrations of eARG, pH values, inorganic anions and humic substances and water matrix. Reusability experiment demonstrated that CNTs + PS exhibited stable degradation performance after multiple uses. These findings offer a new perspective for the efficient degradation of eARG in environmental remediation.

Promotion of antibiotic-resistant genes dissemination by the micro/nanoplastics in the gut of snail Achatina fulica

Terrestrial animal intestines are hotspots for the enrichment of micro/nano plastics (M/NPs) and antibiotic-resistant genes (ARGs). However, little is known about the further impact of M/NPs on the spread of ARGs in animal guts. This study investigates the role of M/NPs (polystyrene) with varying particle sizes (0.082, 42, and 182 μm), concentrations (10 and 100 mg/L), and exposure durations (4 and 16 days) in the ARGs dissemination via conjugation in the edible snail (Achatina fulica) gut. Combination of qPCR with 16S rRNA-based sequencing, we found that PS exposure caused intestinal cell impairment and shifts in the gut microbial community of snails. Conjugation rate increased with PS particle sizes in the snail gut. After 4 days of exposure, significantly higher conjugation rates were observed in the gut exposed to 100 mg/L PS compared to 10 mg/L, however, this trend reversed after 16 days. Consistently, the abundances of conjugation relevant genes trfA and trbB shared similar trends to the conjugation ratios in the snail gut after PS exposure. Transconjugant diversity was much lower in 10 mg/L PS groups than in 100 mg/L PS treatments. Therefore, this study suggests that the presence of M/NPs would complicate management of ARG spread. The selection pressure exerted by M/NPs may sustain or even amplify the spread of ARGs in the gut of terrestrial animals even in the absence of antibiotics. It highlights the necessity of avoiding M/NPs intake as a part of comprehensive strategy for cubing ARG dissemination in the gut of animals.

Biofilm formation on microplastics and interactions with antibiotics, antibiotic resistance genes and pathogens in aquatic environment

Microplastics (MPs) in aquatic environments easily support biofilm development, which can interact with other environmental pollutants and act as harbors for microorganisms. Recently, numerous studies have investigated the fate and behavior of MP biofilms in aquatic environments, highlighting their roles in the spread of pathogens and antibiotic resistance genes (ARGs) to aquatic organisms and new habitats. The prevalence and effects of MP biofilms in aquatic environments have been extensively investigated in recent decades, and their behaviors in aquatic environments need to be synthesized systematically with updated information. This review aims to reveal the development of MP biofilm and its interactions with antibiotics, ARGs, and pathogens in aquatic environments. Recent research has shown that the adsorption capabilities of MPs to antibiotics are enhanced after the biofilm formation, and the adsorption of biofilms to antibiotics is biased towards chemisorption. ARGs and microorganisms, especially pathogens, are selectively enriched in biofilms and significantly different from those in surrounding waters. MP biofilm promotes the propagation of ARGs through horizontal gene transfer (HGT) and vertical gene transfer (VGT) and induces the emergence of antibiotic-resistant pathogens, resulting in increased threats to aquatic ecosystems and human health. Some future research needs and strategies in this review are also proposed to better understand the antibiotic resistance induced by MP biofilms in aquatic environments.

Microbiome regulation for sustainable wastewater treatment

Sustainable wastewater treatment is essential for attaining clean water and sanitation, aligning with UN Sustainable Development Goals. Wastewater treatment plants (WWTPs) have utilized environmental microbiomes in biological treatment processes in this effort for over a century. However, the inherent complexity and redundancy of microbial communities, and emerging chemical and biological contaminants, challenge the biotechnology applications. Over the past decades, understanding and utilization of microbial energy metabolism and interaction relationships have revolutionized the biological system. In this review, we discuss how microbiome regulation strategies are being used to generate actionable performance for low-carbon pollutant removal and resource recovery in WWTPs. The engineering application cases also highlight the real feasibility and promising prospects of the microbiome regulation approaches. In conclusion, we recommend identifying environmental risks associated with chemical and biological contaminants transformation as a prerequisite. We propose the integration of gene editing and enzyme design to precisely regulate microbiomes for the synergistic control of both chemical and biological risks. Additionally, the development of integrated technologies and engineering equipment is crucial in addressing the ongoing water crisis. This review advocates for the innovation of conventional wastewater treatment biotechnology to ensure sustainable wastewater treatment.

Neglected contributors to the transmission of bacterial antibiotic resistance in drinking water: Extracellular antibiotic resistance genes and the natural transformation

Antibiotic resistance genes (ARGs) have increasingly gained recognition as an "emerging contaminant" that poses a threat to the biosafety of drinking water. However, previous researches have primarily focused on the intracellular state of ARGs and rarely investigated the ecological characteristics (e.g., distribution and origin), environmental behavior (spread), and risks of extracellular form (eARGs) within drinking water systems. Therefore, this review evaluated isolation strategies and extraction methods for recovering eARGs from drinking water, elucidated the distribution characteristics of eARGs, and examined their impact on the antibiotic resistome from source water to tap water. We emphasized that chlorination and biological treatments significantly contribute to the prevalence and persistence of eARGs in drinking water. Moreover, we highlighted the role of biological reactors (e.g., biofilter, biological activated carbon) and drinking water distribution systems in facilitating the natural transformation of eARGs while significantly contributing to bacterial antibiotic resistance (BAR) propagation. Finally, we summarized the current risk assessment systems for ARGs and critically address remaining challenging questions necessary for better forecasting health risks associated with eARGs in drinking water environments. Collectively, this review enhances the understanding of ecological characteristics and environmental behavior of eARGs in drinking water while providing important implications for controlling and reducing BAR contamination not only in drinking water but also in other aquatic environments.

Water temperature disturbance alters the conjugate transfer of antibiotic resistance genes via affecting ROS content and intercellular aggregation

Spread of antibiotic resistance genes (ARGs) in aquatic ecosystems poses a significant global challenge to public health. The potential effects of water temperature perturbation induced by specific water environment changes on ARGs transmission are still unclear. The conjugate transfer of plasmid-mediated ARGs under water temperature perturbation was investigated in this study. The conjugate transfer frequency (CTF) was only 7.16 × 10-7 at a constant water temperature of 5 °C, and it reached 2.18 × 10-5 at 30 °C. Interestingly, compared to the constant 5 °C, the water temperature perturbations (cooling and warming models between 5-30 °C) significantly promoted the CTF. Intracellular reactive oxygen species was a dominant factor, which not only directly affected the CTF of ARGs, but also functioned indirectly via influencing the cell membrane permeability and cell adhesion. Compared to the constant 5 °C, water temperature perturbations significantly elevated the gene expression associated with intercellular contact, cell membrane permeability, oxidative stress responses, and energy driven force for CTF. Furthermore, based on the mathematical model predictions, the stabilization times of acquiring plasmid maintenance were shortened to 184 h and 190 h under cooling and warming model, respectively, thus the water temperature perturbations promoted the ARGs transmission in natural conditions compared with the constant low temperature conditions.

Ketoprofen promotes the conjugative transfer of antibiotic resistance among antibiotic resistant bacteria in natural aqueous environments

The emergence and spread of antibiotic resistance in the environment pose a serious threat to global public health. It is acknowledged that non-antibiotic stresses, including disinfectants, pharmaceuticals and organic pollutants, play a crucial role in horizontal transmission of antibiotic resistance genes (ARGs). Despite the widespread presence of non-steroidal anti-inflammatory drugs (NSAIDs), notably in surface water, their contributions to the transfer of ARGs have not been systematically explored. Furthermore, previous studies have primarily concentrated on model strains to investigate whether contaminants promote the conjugative transfer of ARGs, leaving the mechanisms of ARG transmission among antibiotic resistant bacteria in natural aqueous environments under the selective pressures of non-antibiotic contaminants remains unclear. In this study, the Escherichia coli (E. coli) K12 carrying RP4 plasmid was used as the donor strain, indigenous strain Aeromonas veronii containing rifampicin resistance genes in Taihu Lake, and E. coli HB101 were used as receptor strains to establish inter-genus and intra-genus conjugative transfer systems, examining the conjugative transfer frequency under the stress of ketoprofen. The results indicated that ketoprofen accelerated the environmental spread of ARGs through several mechanisms. Ketoprofen promoted cell-to-cell contact by increasing cell surface hydrophobicity and reducing cell surface charge, thereby mitigating cell-to-cell repulsion. Furthermore, ketoprofen induced increased levels of reactive oxygen species (ROS) production, activated the DNA damage-induced response (SOS), and enhanced cell membrane permeability, facilitating ARG transmission in intra-genus and inter-genus systems. The upregulation of outer membrane proteins, oxidative stress, SOS response, mating pair formation (Mpf) system, and DNA transfer and replication (Dtr) system related genes, as well as the inhibition of global regulatory genes, all contributed to higher transfer efficiency under ketoprofen treatment. These findings served as an early warning for a comprehensive assessment of the roles of NSAIDs in the spread of antibiotic resistance in natural aqueous environments.

Microplastic biofilms promote the horizontal transfer of antibiotic resistance genes in estuarine environments

As emerging pollutants, microplastics can aggregate microorganisms on their surfaces and form biofilms, enriching antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs). Consequently, microplastic biofilms have become a focal point of research. Horizontal gene transfer is one of the primary mechanisms by which bacteria acquire antibiotic resistance, with much of the research focusing on suspended bacteria. However, microplastic biofilms, as hotspots for horizontal gene transfer, also merit significant investigation. This study primarily explored and compared the frequency of ARG conjugative transfer between suspended bacteria and microplastic biofilms. The results demonstrated that, compared to suspended bacteria, microplastic biofilms enhanced the frequency of ARG conjugative transfer by 7.2-19.6 times. Among them, biofilms on polyethylene microplastics showed the strongest promotion of conjugation. After the formation of microplastic biofilms, there was a significant increase in bacterial density within the biofilms, which raised the collision frequency of donor and recipient bacteria. Then microplastic biofilms facilitated the gene expression levels of outer membrane proteins, enhanced bacterial gene transfer capabilities, promoted the synthesis of conjugative pili, accelerated the formation of conjugative pairing systems, and elevated the expression levels of genes related to DNA replication and transfer systems, thereby enhancing the conjugative transfer of ARGs within microplastic biofilms. Among different types of microplastic biofilms, polyethylene biofilms exhibited the highest bacterial density, thus showing the highest frequency of ARG conjugation. This study highlights the risks associated with ARG conjugative transfer following the formation of microplastic biofilms and provides insights into the risks of microplastic and antibiotic resistance propagation in estuarine environments.

How micro-/nano-plastics influence the horizontal transfer of antibiotic resistance genes - A review

Plastic debris such as microplastics (MPs) and nanoplastics (NPTs), along with antibiotic resistance genes (ARGs), are pervasive in the environment and are recognized as significant global health and ecological concerns. Micro-/nano-plastics (MNPs) have been demonstrated to favor the spread of ARGs by enhancing the frequency of horizontal gene transfer (HGT) through various pathways. This paper comprehensively and systematically reviews the current study with focus on the influence of plastics on the HGT of ARGs. The critical role of MNPs in the HGT of ARGs has been well illustrated in sewage sludge, livestock farms, constructed wetlands and landfill leachate. A summary of the performed HGT assay and the underlying mechanism of plastic-mediated transfer of ARGs is presented in the paper. MNPs could facilitate or inhibit HGT of ARGs, and their effects depend on the type, size, and concentration. This review provides a comprehensive insight into the effects of MNPs on the HGT of ARGs, and offers suggestions for further study. Further research should attempt to develop a standard HGT assay and focus on investigating the impact of different plastics, including the oligomers they released, under real environmental conditions on the HGT of ARGs.

Disinfection and post-disinfection conditions drive bacterial and viral evolution across the environment and host

Water disinfection practices have long been established as a critical engineering intervention for controlling pathogen transmission and safeguarding individual and public health. However, recent discoveries have unveiled the significant role disinfection and post-disinfection play in accelerating the development of resistance to disinfectants and antimicrobial drugs within bacterial and viral communities in the environment. This phenomenon, in turn, may facilitate the emergence of persistent microbes and those with new genetic characteristics. These microbes may thrive in host environments with increased infectivity and resistance, posing challenges to current medical treatments and jeopardizing human health. In this perspective, we illuminate the intricate interplay between aquatic environments, microbes, and hosts and how microbial virulence evolves across the environment and host under the pressure of disinfection and post-disinfection conditions. We aim to draw attention to the previously overlooked potential risks associated with disinfection in driving the virulence evolution of bacteria and viruses, establish connections between pathogens in diverse environments and hosts within the overarching framework of the One Health concept, and ultimately provide guidelines for advancing future water disinfection technologies to effectively curb the spread of infectious diseases.

Assessment of chlorine and hydrogen peroxide on airborne bacteria: Disinfection efficiency and induction of antibiotic resistance

Airborne pathogens severely threaten public health worldwide. Air disinfection is essential to ensure public health. However, excessive use of disinfectants may endanger environmental and ecological security due to the residual disinfectants and their by-products. This study systematically evaluated disinfection efficiency, induction of multidrug resistance, and the underlying mechanisms of disinfectants (NaClO and H2O2) on airborne bacteria. The results showed that airborne bacteria were effectively inactivated by atomized NaClO (>160 μg/L) and H2O2 (>320 μg/L) after 15 min. However, some bacteria still survived after disinfection by atomized NaClO (0-80 μg/L) and H2O2 (0-160 μg/L), and they exhibited significant increases in antibiotic resistance. The whole-genome sequencing of the resistant bacteria revealed distinct mutations that were responsible for both antibiotic resistance and virulence. This study also provided evidences and insights into possible mechanisms underlying the induction of antibiotic resistance by air disinfection, which involved intracellular reactive oxygen species formation, oxidative stress responses, alterations in bacterial membranes, activation of efflux pumps, and the thickening of biofilms. The present results also shed light on the role of air disinfection in inducing antibiotic resistance, which could be a crucial factor contributing to the global spread of antibiotic resistance through the air.

The Role of Wastewater Treatment Plants in Dissemination of Antibiotic Resistance: Source, Measurement, Removal and Risk Assessment

Antibiotic Resistance Genes (ARGs) are contaminants of emerging concern with marked potential to impact public and environmental health. This review focusses on factors that influence the presence, abundance, and dissemination of ARGs within Wastewater Treatment Plants (WWTPs) and associated effluents. Antibiotic-Resistant Bacteria (ARB) and ARGs have been detected in the influent and the effluent of WWTPs worldwide. Different levels of wastewater treatment (primary, secondary, and tertiary) show different degrees of removal efficiency of ARGs, with further differences being observed when ARGs are captured as intracellular or extracellular forms. Furthermore, routinely used molecular methodologies such as quantitative polymerase chain reaction or whole genome sequencing may also vary in resistome identification and in quantifying ARG removal efficiencies from WWTP effluents. Additionally, we provide an overview of the One Health risk assessment framework, as well as future strategies on how WWTPs can be assessed for environmental and public health impact.

Dissolved oxygen facilitates efficiency of chlorine disinfection for antibiotic resistance

Controlling the dissemination of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) is a global concern. While commonly used chlorine disinfectants can damage or even kill ARB, dissolved oxygen (DO) may affect the formation of reactive chlorine species. This leads to the hypothesis that DO may play roles in mediating the effectiveness of chlorine disinfection for antibiotic resistance. To this end, this study investigated the impacts of DO on the efficiency of chlorine disinfection for antibiotic resistance. The results revealed that DO could increase the inactivation efficiency of ARB under chloramine and free chlorine exposure at practically relevant concentrations. Reactive species induced by DO, including H2O2, O2-, and OH, inactivated ARB strains by triggering oxidative stress response and cell membrane damage. In addition, the removal efficiency of extracellular ARGs (i.e. tetA and blaTEM) was enhanced with increasing dosage of free chlorine or chloramine under aerobic conditions. DO facilitated the fragmentation of plasmids, contributing to the degradation of extracellular ARGs under exposure to chlorine disinfectants. The findings suggested that DO facilitates disinfection efficiency for antibiotic resistance in water treatment systems.

Deciphering the reduction of antibiotic resistance genes (ARGs) during medium-chain fatty acids production from waste activated sludge: Driven by inhibition of ARGs transmission and shift of microbial community

Medium-chain fatty acids (MCFAs) production from waste activated sludge (WAS) by chain extension (CE) is a promising technology. However, the effects and mechanisms of CE process on the fate of antibiotic resistance genes (ARGs) remain unclear. In this study, the results showed that the removal efficiency of ARGs was 81.15 % in CE process, suggesting its efficacy in reducing environmental risks. Further, the observed decrease in mobile genetic elements (MGEs) indicated that CE process restricted the horizontal gene transfer (HGT). Complementing this, the increase in soluble organic matters and extracellular 16 S rDNA confirmed that MCFAs production caused bacterial damage. Decreased intracellular ARGs and increased extracellular ARGs further revealed that MCFAs production impaired ARGs hosts, thereby limiting the vertical gene transfer (VGT) of ARGs. Shift of microbial community combined with co-occurrence network analysis demonstrated that functional bacteria without host potential for ARGs were enriched, but potential ARGs and MGEs hosts decreased, showing the role of functional bacterial phylogeny and selection pressure of MCFAs in reducing ARGs. Finally, partial least squares path model was used to systematic verify the mechanism of ARGs removal in CE process, which was attributed to the inhibition of ARGs transmission (HGT and VGT) and shift of microbial community.

Mechanisms of conjugative transfer of antibiotic resistance genes induced by extracellular polymeric substances: Insights into molecular diversities and electron transfer properties

Dissemination of antibiotic resistance genes (ARGs) has become a critical threat to public health. Activated sludge, rich in extracellular polymeric substances (EPS), is an important pool of ARGs. In this study, mechanisms of conjugation transfer of ARGs induced by EPS, including tightly bound EPS (TBEPS), soluble EPS (SEPS), and loosely bound EPS (LBEPS), were explored in terms of molecular diversities and electron transfer properties of EPS. Conjugation transfer frequency was increased by 9.98-folds (SEPS), 4.21-folds (LBEPS), and 15.75-folds (TBEPS) versus the control, respectively. Conjugation-related core genes involving SOS responses (9 genes), membrane permeability (18 genes), intercellular contact (17 genes), and energy metabolism pathways (13 genes) were all upregulated, especially in the presence of TBEPS. Carbohydrates and aliphatic substances in SEPS and LBEPS were contributors to ARG transfer, via influencing reactive oxygen species (ROS) formation (SEPS) and ROS and adenosine triphosphate (ATP) production (LBEPS). TBEPS had the highest redox potential and greatest lability and facilitated electron transfer and alternated respiration between cells, thus promoting ARG transfer by producing ATP. Generally, the chemical molecular characteristics and redox properties of EPS facilitated ARG transfer mainly by influencing lipid peroxidation and ATP, respectively.

Unraveling the effect of micro/nanoplastics on the occurrence and horizontal transfer of environmental antibiotic resistance genes: Advances, mechanisms and future prospects

Microplastics can not only serve as vectors of antibiotic resistance genes (ARGs), but also they and even nanoplastics potentially affect the occurrence of ARGs in indigenous environmental microorganisms, which have aroused great concern for the development of antibiotic resistance. This article specifically reviews the effects of micro/nanoplastics (concentration, size, exposure time, chemical additives) and their interactions with other pollutants on environmental ARGs dissemination. The changes of horizontal genes transfer (HGT, i.e., conjugation, transformation and transduction) of ARGs caused by micro/nanoplastics were also summarized. Further, this review systematically sums up the mechanisms of micro/nanoplastics regulating HGT process of ARGs, including reactive oxygen species production, cell membrane permeability, transfer-related genes expression, extracellular polymeric substances production, and ARG donor-recipient adsorption/contaminants adsorption/biofilm formation. The underlying mechanisms in changes of bacterial communities induced by micro/nanoplastics were also discussed as it was an important factor for structuring the profile of ARGs in the actual environment, including causing environmental stress, providing carbon sources, forming biofilms, affecting pollutants distribution and environmental factors. This review contributes to a systematical understanding of the potential risks of antibiotic resistance dissemination caused by micro/nanoplastics and provokes thinking about perspectives for future research and the management of micro/nanoplastics and plastics.

Dynamics of antimicrobial resistance and susceptibility profile in full-scale hospital wastewater treatment plants

Drug resistance has become a matter of great concern, with many bacteria now resist multiple antibiotics. This study depicts the occurrence of antibiotic-resistant bacteria (ARB) and resistance patterns in five full-scale hospital wastewater treatment plants (WWTPs). Samples of raw influent wastewater, as well as pre- and post-disinfected effluents, were monitored for targeted ARB and resistance genes in September 2022 and February 2023. Shifts in resistance profiles of Escherichia coli, Pseudomonas aeruginosa, and Acinetobacter baumannii antimicrobial-resistant indicators in the treated effluent compared to that in the raw wastewater were also worked out. Ceftazidime (6.78 × 105 CFU/mL) and cefotaxime (6.14 × 105 CFU/mL) resistant species showed the highest concentrations followed by ciprofloxacin (6.29 × 104 CFU/mL), and gentamicin (4.88 × 104 CFU/mL), in raw influent respectively. WWTP-D employing a combination of biological treatment and coagulation/clarification for wastewater decontamination showed promising results for reducing ARB emissions from wastewater. Relationships between treated effluent quality parameters and ARB loadings showed that high BOD5 and nitrate levels were possibly contributing to the persistence and/or selection of ARBs in WWTPs. Furthermore, antimicrobial susceptibility tests of targeted species revealed dynamic shifts in resistance profiles through treatment processes, highlighting the potential for ARB and ARGs in hospital wastewater to persist or amplify during treatment.

EDTA enables to alleviate impacts of metal ions on conjugative transfer of antibiotic resistance genes

Various heavy metals are reported to be able to accelerate horizontal transfer of antibiotic resistance genes (ARGs). In real water environmental settings, ubiquitous complexing agents would affect the environmental behaviors of heavy metal ions due to the formation of metal-organic complexes. However, little is known whether the presence of complexing agents would change horizontal gene transfer due to heavy metal exposure. This study aimed to fill this gap by investigating the impacts of a typical complexing agent ethylenediaminetetraacetic acid (EDTA) on the conjugative transfer of plasmid-mediated ARGs induced by a range of heavy metal ions. At the environmentally relevant concentration (0.64 mg L-1) of metal ions, all the tested metal ions (Mg2+, Ca2+, Co2+, Pb2+, Ni2+, Cu2+, and Fe3+) promoted conjugative transfer of ARGs, while an inhibitory effect was observed at a relatively higher concentration (3.20 mg L-1). In contrast, EDTA (0.64 mg L-1) alleviated the effects of metal ions on ARGs conjugation transfer, evidenced by 11 %-66 % reduction in the conjugate transfer frequency. Molecular docking and dynamics simulations disclosed that this is attributed to the stronger binding of metal ions with the lipids in cell membranes. Under metal-EDTA exposure, gene expressions related to oxidative stress response, cell membrane permeability, intercellular contact, energy driving force, mobilization, and channels of plasmid transfer were suppressed compared with the metal ions exposure. This study offers insights into the alleviation mechanisms of complexing agents on ARGs transfer induced by free metal ions.

Efficacy and Mechanism of Antibiotic Resistance Gene Degradation and Cell Membrane Damage during Ultraviolet Advanced Oxidation Processes

Combinations of UV with oxidants can initiate advanced oxidation processes (AOPs) and enhance bacterial inactivation. However, the effectiveness and mechanisms of UV-AOPs in damaging nucleic acids (e.g., antibiotic resistance genes (ARGs)) and cell integrity represent a knowledge gap. This study comprehensively compared ARG degradation and cell membrane damage under three different UV-AOPs. The extracellular ARG (eARG) removal efficiency followed the order of UV/chlorine > UV/H2O2 > UV/peracetic acid (PAA). Hydroxyl radical (•OH) and reactive chlorine species (RCS) largely contributed to eARG removal, while organic radicals made a minor contribution. For intracellular ARGs (iARGs), UV/H2O2 did not remove better than UV alone due to the scavenging of •OH by cell components, whereas UV/PAA provided a modest synergism, likely due to diffusion of PAA into cells and intracellular •OH generation. Comparatively, UV/chlorine achieved significant synergistic iARG removal, suggesting the critical role of the RCS in resisting cellular scavenging and inactivating ARGs. Additionally, flow cytometry analysis demonstrated that membrane damage was mainly attributed to chlorine oxidation, while the impacts of radicals, H2O2, and PAA were negligible. These results provide mechanistic insights into bacterial inactivation and fate of ARGs during UV-AOPs, and shed light on the suitability of quantitative polymerase chain reaction (qPCR) and flow cytometry in assessing disinfection performance.

Pyrite from acid mine drainage promotes the removal of antibiotic resistance genes and mobile genetic elements in karst watershed with abundant calcium carbonate

More information is needed to fully comprehend how acid mine drainage (AMD) affects the phototransformation of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in karst water and sewage-irrigated farmland soil with abundant carbonate rocks (CaCO3) due to increasing pollution of AMD formed from pyrite (FeS2). The results showed FeS2 accelerated the inactivation of ARB with an inactivation of 8.7 log. Notably, extracellular and intracellular ARGs and mobile genetic elements (MGEs) also experienced rapid degradation. Additionally, the pH of the solution buffered by CaCO3 significantly influenced the photo-inactivation of ARB. The Fe2+ in neutral solution was present in Fe(II) coordination with strong reducing potential and played a crucial role in generating •OH (7.0 μM), which caused severe damage to ARB, ARGs, and MGEs. The •OH induced by photo-Fenton of FeS2 posed pressure to ARB, promoting oxidative stress response and increasing generation of reactive oxygen species (ROS), ultimately damaging cell membranes, proteins and DNA. Moreover, FeS2 contributed to a decrease in MIC of ARB from 24 mg/L to 4 mg/L. These findings highlight the importance of AMD in influencing karst water and sewage-irrigated farmland soil ecosystems. They are also critical in advancing the utilization of FeS2 to inactivate pathogenic bacteria.

Identification of extracellular polymeric substances layer barrier in chloroquine phosphate-disturbed anammox consortia and mechanism dissection on cytotoxic behavior by computational chemistry

The over-dosing use of chloroquine phosphate (CQ) poses severe threats to human beings and ecosystem due to the high persistence and biotoxicity. The discharge of CQ into wastewater would affect the biomass activity and process stability during the biological processes, e.g., anammox. However, the response mechanism of anammox consortia to CQ remain unknown. In this study, the accurate role of extracellular polymeric substances barrier in attenuating the negative effects of CQ, and the mechanism on cytotoxic behavior were dissected by molecular spectroscopy and computational chemistry. Low concentrations (≤6.0 mg/L) of CQ hardly affected the nitrogen removal performance due to the adaptive evolution of EPS barrier and anammox bacteria. Compact protein of EPS barrier can bind more CQ (0.24 mg) by hydrogen bond and van der Waals force, among which O-H and amide II region respond CQ binding preferentially. Importantly, EPS contributes to the microbiota reshape with selectively enriching Candidatus_Kuenenia for self-protection. Furthermore, the macroscopical cytotoxic behavior was dissected at a molecular level by CQ fate/distribution and computational chemistry, suggesting that the toxicity was ascribed to attack of CQ on functional proteins of anammox bacteria with atom N17 (f-=0.1209) and C2 (f+=0.1034) as the most active electrophilic and nucleophilic sites. This work would shed the light on the fate and risk of non-antibiotics in anammox process.

Chlorite and bromate alter the conjugative transfer of antibiotic resistance genes: Co-regulation of oxidative stress and energy supply

The widespread use of disinfectants during the global response to the 2019 coronavirus pandemic has increased the co-occurrence of disinfection byproducts (DBPs) and antibiotic resistance genes (ARGs). Although DBPs pose major threats to public health globally, there is limited knowledge regarding their biological effects on ARGs. This study aimed to investigate the effects of two inorganic DBPs (chlorite and bromate) on the conjugative transfer of RP4 plasmid among Escherichia coli strains at environmentally relevant concentrations. Interestingly, the frequency of conjugative transfer was initially inhibited when the exposure time to chlorite or bromate was less than 24 h. However, this inhibition transformed into promotion when the exposure time was extended to 36 h. Short exposures to chlorite or bromate were shown to impede the electron transport chain, resulting in an ATP shortage and subsequently inhibiting conjugative transfer. Consequently, this stimulates the overproduction of reactive oxygen species (ROS) and activation of the SOS response. Upon prolonged exposure, the resurgent energy supply promoted conjugative transfer. These findings offer novel and valuable insights into the effects of environmentally relevant concentrations of inorganic DBPs on the conjugative transfer of ARGs, thereby providing a theoretical basis for the management of DBPs.

Effect of environmental factors on conjugative transfer of antibiotic resistance genes in aquatic settings

Antimicrobial-resistance genes (ARGs) are spread among bacteria by horizontal gene transfer, however, the effect of environmental factors on the dynamics of the ARG in water environments has not been very well understood. In this systematic review, we employed the regression tree algorithm to identify the environmental factors that facilitate/inhibit the transfer of ARGs via conjugation in planktonic/biofilm-formed bacterial cells based on the results of past relevant research. Escherichia coli strains were the most studied genus for conjugation experiments as donor/recipient in the intra-genera category. Conversely, Pseudomonas spp., Acinetobacter spp., and Salmonella spp. were studied primarily as recipients across inter-genera bacteria. The conjugation efficiency (ce) was found to be highly dependent on the incubation period. Some antibiotics, such as nitrofurantoin (at ≥0.2 µg ml-1) and kanamycin (at ≥9.5 mg l-1) as well as metallic compounds like mercury (II) chloride (HgCl2, ≥3 µmol l-1), and vanadium (III) chloride (VCl3, ≥50 µmol l-1) had enhancing effect on conjugation. The highest ce value (-0.90 log10) was achieved at 15°C-19°C, with linoleic acid concentrations <8 mg l-1, a recognized conjugation inhibitor. Identifying critical environmental factors affecting ARG dissemination in aquatic environments will accelerate strategies to control their proliferation and combat antibiotic resistance.

Using UV/peracetic acid as pretreatment for subsequent bio-treatment of antibiotic-containing wastewater treatment: Mitigating microbial inhibition and antibiotic resistance genes proliferation

UV/peracetic acid (PAA) treatment presents a promising approach for antibiotic removal, but its effects on microbial community and proliferation of antibiotic resistance genes (ARGs) during the subsequent bio-treatment remain unclear. Thus, we evaluated the effects of the UV/PAA on tetracycline (TTC) degradation, followed by introduction of the treated wastewater into the bio-treatment system to monitor changes in ARG expression and biodegradability. Results demonstrated effective TTC elimination by the UV/PAA system, with carbon-centered radicals playing a significant role. Crucially, the UV/PAA system not only eliminated antibacterial activity but also inhibited potential ARG host growth, thereby minimizing the emergence and dissemination of ARGs during subsequent bio-treatment. Additionally, the UV/PAA system efficiently removed multi-antibiotic resistant bacteria and ARGs from the bio-treatment effluent, preventing ARGs from being released into the environment. Hence, we propose a multi-barrier strategy for treating antibiotic-containing wastewater, integrating UV/PAA pre-treatment and post-disinfection with bio-treatment. The inhibition of ARGs transmission by the integrated system was verified through actual soil testing, confirming its effectiveness in preventing ARGs dissemination in the surrounding natural ecosystem. Overall, the UV/PAA treatment system offers a promising solution for tackling ARGs challenges by controlling ARGs proliferation at the source and minimizing their release at the end of the treatment process.

The fate of antibiotic resistance genes in wastewater containing microalgae treated by chlorination, ultra-violet, and Fenton reaction

Antibiotic resistance genes (ARGs) and bacteria (ARBs) in the effluent of wastewater treatment plants (WWTPs) are of utmost importance for the dissemination of ARGs in natural aquatic environments. Therefore, there is an urgent need for effective technologies to eliminate WWTP ARGs/ARBs and mitigate the associated risks posed by the discharged ARG in aquatic environments. To test the effective technology for eliminating ARGs/ARBs, we compared the removal of ARGs and ARBs by three different tertiary treatments, namely ultra-violet (UV) disinfection, chlorination disinfection, and Fenton oxidation. Then, the treated wastewater was co-cultured with Chlorella vulgaris (representative of aquatic biota) to investigate the fate of discharged ARGs into the aquatic environment. The results demonstrated that chlorination (at a chlorine concentration of 15 mg/L) and Fenton (at pH 2.73, with 0.005 mol/L Fe2+ and 0.0025 mol/L H2O2) treatment showed higher efficacy in ARG removal (1.8 - 4.17 logs) than UV treatment (15 min) (1.29 - 3.87 logs). Moreover, chlorine at 15 mg/L and Fenton treatment effectively suppressed ARB regeneration while UV treatment for 15 min could not. Regardless of treatments tested in this study, the input of treated wastewater to the Chlorella system increased the number of ARGs and mobile genetic elements (MGEs), indicating the potential risk of ARG dissemination associated with WWTP discharge. Among the wastewater-Chlorella co-culture systems, chlorination resulted in less of an increase in the number of ARGs and MGEs compared to Fenton and UV treatment. When comparing the wastewater systems to the co-culture systems, it was observed that Chlorella vulgaris reduced the number of ARGs and MGEs in chlorination and UV-treated wastewater; however, Chlorella vulgaris promoted ARG survival in Fenton-treated water, suggesting that aquatic microalgae might act as a barrier to ARG dissemination. Overall, chlorination treatment not only effectively removes ARGs and inhibits ARB regeneration but also shows a lower risk of ARG dissemination. Therefore, chlorination is recommended for practical application in controlling the spread of discharged ARGs from WWTP effluent in natural aquatic environments.

Regulation of quorum sensing for the manipulation of conjugative transfer of antibiotic resistance genes in wastewater treatment system

The emergence and transmission of antibiotic resistance genes (ARGs) through plasmid-mediated conjugation has become a significant worldwide public health threat. Biofilms are widely recognized as the primary reservoirs for ARGs, providing favorable conditions for horizontal gene transfer. Quorum sensing (QS) plays a critical role in bacterial biofilm formation, which further influences the spread of bacterial resistance. In this study, we examined the effects of vanillin, a QS inhibitor (QSI), at subinhibitory concentrations (sub-MICs) ranging from 0 - 0.1 g/L, on the transfer of ARGs between Escherichia coli and Pseudomonas aeruginosa. Our findings indicated that vanillin at sub-MICs inhibited the conjugative transfer frequency of the RP4 plasmid. This inhibition was supported by the downregulation of plasmid transfer genes. The suppression of conjugation can mainly be attributed to the inhibition of biofilm formation, the synthesis of extracellular polymeric substances (EPS), and the secretion of virulence factors, all of which are regulated by the bacterial QS system. On the other hand, the levels of ROS and cell membrane permeability were not primary explanations for this phenomenon. Furthermore, vanillin also reduced the conjugative transfer frequency of ARGs in wastewater effluent, providing a potential approach to alleviate bacterial resistance in water environments. These findings underscore the regulatory role of QSI in controlling ARGs transfer and have significant implications for manipulating the dissemination of bacterial resistance in the environment.

Microplastic pollution interaction with disinfectant resistance genes: research progress, environmental impacts, and potential threats

The consumption of disposable plastic products and disinfectants has surged during the global COVID-19 pandemic, as they play a vital role in effectively preventing and controlling the spread of the virus. However, microplastic pollution and the excessive or improper use of disinfectants contribute to the increased environmental tolerance of microorganisms. Microplastics play a crucial role as vectors for microorganisms and plankton, facilitating energy transfer and horizontal gene exchange. The increase in the use of disinfectants has become a driving force for the growth of disinfectant resistant bacteria (DRB). A large number of microorganisms can have intense gene exchange, such as plasmid loss and capture, phage transduction, and cell fusion. The reproduction and diffusion rate of DRB in the environment is significantly higher than that of ordinary microorganisms, which will greatly increase the environmental tolerance of DRB. Unfortunately, there is still a huge knowledge gap in the interaction between microplastics and disinfectant resistance genes (DRGs). Accordingly, it is critical to comprehensively summarize the formation and transmission routes of DRGs on microplastics to address the problem. This paper systematically analyzed the process and mechanisms of DRGs formed by microbes. The interaction between microplastics and DRGs and the contribution of microplastic on the diffusion and spread of DRGs were expounded. The potential threats to the ecological environment and human health were also discussed. Additionally, some challenges and future priorities were also proposed with a view to providing useful basis for further research.

The role of water matrix on antibiotic resistance genes transmission in substrate layer from stormwater bioretention cells

Recently, extensive attention has been paid to antibiotic resistance genes (ARGs) transmission. However, little available literature could be found about ARGs transmission in stormwater bioretention cells, especially the role of water matrix on ARGs transmission. Batch experiments were conducted to investigate target ARGs (blaTEM, tetR and aphA) transmission behaviors in substrate layer from stormwater bioretention cells under different water matrices, including nutrient elements (e.g., carbon, nitrogen and phosphorus), water environmental conditions (dissolved oxygen (DO), pH and salinity, etc.) and pollution factors (like heavy metals, antibiotics and disinfectants), showing that ARGs conjugation frequency increased sharply with the enhancement of water matrices (expect DO and pH), while there were obvious increasing tendencies for all ARGs transformation frequencies under only the pollution factor. The correlation between dominant bacteria and ARGs transmission implied that conjugation and transformation of ARGs were mainly determined by Firmicutes, Bacteroidota, Latescibacterota, Chloroflexi and Cyanobacteria at the phylum level, and by Sphingomonas, Ensifer, IMCC26256, Rubellimicrobium, Saccharimonadales, Vicinamibacteraceae, Nocardioides, JG30-KF-CM66 at the genus level. The mentioned dominant bacteria were responsible for intracellular reactive oxygen species (ROS) and cell membrane permeability (CMP) in the substrate layer, where the amplification of intracellular ROS variation were the largest with 144 and 147 % under the condition of TP and salinity, respectively, and the one of CMP variation were the highest more than 165 % under various pollution factors. Furthermore, both increasing DO and reducing salinity could be potential approaches for the inhibition of ARGs transmission in bioretention cells taking into account the simultaneous removal of conventional pollutants.

Emerging contaminants in the water environment: Disinfection-induced viable but non-culturable waterborne pathogens

Disinfection is essential for the control of waterborne pathogens (WPs), especially during the COVID-19 pandemic. WP can enter the viable but non-culturable (VBNC) state to evade disinfection, seriously threatening water safety. VBNC WPs should be considered as an emerging contaminant to ensure a higher level of safety of the water environment. Here, this study systematically reviewed the water disinfection methods that could induce WPs into the VBNC state, and clarified the risks of different species of VBNC WPs in the relevant water environment. The physicochemical and physiological properties of VBNC cells (e.g., morphology, physiology, and resuscitation potential) were then evaluated to better understand their potential health risks. In addition, the dominant detection methods of VBNC WPs were discussed, and real-time and label-free technologies were recommended for the study of VBNC WPs in the aquatic environment. The possible mechanisms of formation and persistence at the genetic level were highlighted. It concluded that the VBNC state has a deeper level of dormancy than the persistent state, which is associated with the general stress response and stringent response systems, and its persistence is also associated with the active efflux of harmful substances. Finally, the current shortcomings and research perspectives of VBNC bacteria were summarized. This review provides new insights into the characteristics, detection methods, persistence mechanisms, and potential health risks of VBNC WPs induced by water disinfection processes, and also serves as a basis for microbial risk control in the aquatic environment.

Sulfate availability drives the reductive transformation of schwertmannite by co-cultured iron- and sulfate-reducing bacteria

Schwertmannite (Sch) is a highly bioavailable iron-hydroxysulfate mineral commonly found in acid mine drainage contaminated environment rich in sulfate (SO42-). Microbial-mediated Sch transformation has been well-studied, however, the understanding of how SO42- availability affects the microbial-mediated Sch transformation and the secondary minerals influence microbes is relatively limited. This study examined the effect of SO42- availability on the iron-reducing bacteria (FeRB) and SO42--reducing bacteria (SRB) consortium-mediated Sch transformation and the resulting secondary minerals in turn on bacteria. Increased SO42- accelerated the onset of microbial SO42- reduction, which significantly accelerated Sch reduction transformation. The extent of intermediate products such as lepidocrocite (22.1 % ~ 76.3 %, all treatments) and goethite (15.3 %, 10 mM SO42-, 5 d) formed by Sch transformation depended on SO42- concentrations. Vivianite, siderite and iron‑sulfur minerals (e.g., FeS and FeS2) were the dominant secondary minerals, in which the relative content of vivianite and siderite decreased while iron‑sulfur minerals increased with increasing SO42- concentration. Correspondingly, the abundance of FeRB and SRB was negatively and positively correlated with SO42- concentration, respectively; 1 mM SO42- promoted the cymA and omcA expression of FeRB, but 10 mM SO42- lowerd the cymA and omcA expression compared to the 1 mM SO42-; the dsr expression of SRB related linearly to the SO42- concentration. These secondary minerals accumulated on the cell surface to form cell encrustations, which limited the growth and gene expression of FeRB and SRB, and even inhibited the activity of SRB in the 10 mM SO42- treatment group. The 10 mM SO42- treatment group with low-intensity ultrasound effectively restored the SRB activity for reducing SO42- by disintegrating the cell-mineral aggregation, further indicating that cell encrustations limited the microbial metabolism. The results highlight the critical role that SO42- availability can play in controlling microbial transformation of mineral, and the influence of secondary minerals on microbial metabolism.

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.

Facet-Specific Photocatalytic Degradation of Extracellular Antibiotic Resistance Genes by Hematite Nanoparticles in Aquatic Environments

The persistence of extracellular antibiotic resistance genes (ARGs) in aquatic environments has attracted increasing attention due to their potential threat to public health and the environment. However, the fate of extracellular ARGs in receiving water remains largely unknown. This study investigated the influence of hematite nanoparticles, a widespread natural mineral, on the photodegradation of extracellular ARGs in river water. Results showed that under exposure to visible light, hematite nanoparticles, at environmental concentrations, resulted in a 3-5 orders of magnitude reduction in extracellular ARGs. This photodegradation of extracellular ARGs is shown to be facet-dependent; the (001) facet of hematite demonstrates a higher removal rate than that of the (100) facet, which is ascribed to its enhanced adsorption capability and higher hydroxyl radical (•OH) production. Density functional theory (DFT) calculations corroborate this finding, indicating elevated iron density, larger adsorption energy, and lower energy barrier of •OH formation on the (001) facet, providing more active sites and •OH generation for extracellular ARG interaction. Gel electrophoresis and atomic force microscopy analyses further confirm that the (001) facet causes more substantial damage to extracellular ARGs than the (100) facet. These findings pave the way for predicting the photodegradation efficiency of hematite nanoparticles with varied facets, thereby shedding light on the inherent self-purification capacity for extracellular ARGs in both natural and engineered aquatic environments.

Can microplastics and disinfectant resistance genes pose conceivable threats to water disinfection process?

Microplastic pollution in the environment has aroused widespread concerns, however, the potential environmental risks caused by excessive use of disinfectants are still unknown. Disinfectants with doses below the threshold can enhance the communication of resistance genes in pathogenic microorganisms, promoting the development and spread of antimicrobial activity. Problematically, the intensification of microplastic pollution and the increase of disinfectant consumption will become a key driving force for the growth of disinfectant resistance bacteria (DRB) and disinfectant resistance genes (DRGs) in the environment. Disinfection plays a crucial role in ensuring water safety, however, the presence of microplastics and DRGs seriously disturb the water disinfection process. Microplastics can reduce the concentration of disinfectant in the local environment around microorganisms and improve their tolerance. Microorganisms can improve their resistance to disinfectants or generate resistance genes via phenotypic adaptation, gene mutations, and horizontal gene transfer. However, very limited information is available on the impact of DRB and DRGs on disinfection process. In this paper, the contribution of microplastics to the migration and transmission of DRGs was analyzed. The challenges posed by the presence of microplastics and DRGs on conventional disinfection were thoroughly discussed. The knowledge gaps faced by relevant current research and further research priorities have been proposed in order to provide a scientific basis in the future.

Comprehensive insights into antibiotic resistance gene migration in microalgal-bacterial consortia: Mechanisms, factors, and perspectives

With the overuse of antibiotics, antibiotic resistance gene (ARG) prevalence is gradually increasing. ARGs are considered emerging contaminants that are broadly concentrated and dispersed in most aquatic environments. Recently, interest in microalgal-bacterial biotreatment of antibiotics has increased, as eukaryotes are not the primary target of antimicrobial drugs. Moreover, research has shown that microalgal-bacterial consortia can minimize the transmission of antibiotic resistance in the environment. Unfortunately, reviews surrounding the ARG migration mechanism in microalgal-bacterial consortia have not yet been performed. This review briefly introduces the migration of ARGs in aquatic environments. Additionally, an in-depth summary of horizontal gene transfer (HGT) between cyanobacteria and bacteria and from bacteria to eukaryotic microalgae is presented. Factors influencing gene transfer in microalgal-bacterial consortia are discussed systematically, including bacteriophage abundance, environmental conditions (temperature, pH, and nutrient availability), and other selective pressure conditions including nanomaterials, heavy metals, and pharmaceuticals and personal care products. Furthermore, considering that quorum sensing could be involved in DNA transformation by affecting secondary metabolites, current knowledge surrounding quorum sensing regulation of HGT of ARGs is summarized. In summary, this review gives valuable information to promote the development of practical and innovative techniques for ARG removal by microalgal-bacterial consortia.

Assessing the nonlinear association of environmental factors with antibiotic resistance genes (ARGs) in the Yangtze River Mouth, China

The emergence of antibacterial resistance (ABR) is an urgent and complex public health challenge worldwide. Antibiotic resistant genes (ARGs) are considered as a new pollutant by the WHO because of their wide distribution and emerging prevalence. The role of environmental factors in developing ARGs in bacterial populations is still poorly understood. Therefore, the relationship between environmental factors and bacteria should be explored to combat ABR and propose more tailored solutions in a specific region. Here, we collected and analyzed surface water samples from Yangtze Delta, China during 2021, and assessed the nonlinear association of environmental factors with ARGs through a sigmoid model. A high abundance of ARGs was detected. Amoxicillin, phosphorus (P), chromium (Cr), manganese (Mn), calcium (Ca), and strontium (Sr) were found to be strongly associated with ARGs and identified as potential key contributors to ARG detection. Our findings suggest that the suppression of ARGs may be achieved by decreasing the concentration of phosphorus in surface water. Additionally, Group 2A light metals (e.g., magnesium and calcium) may be candidates for the development of eco-friendly reagents for controlling antibiotic resistance in the future.

The factors controlling antibiotic resistance genes in different treatment processes of mainstream full-scale wastewater treatment plants

The alteration of antibiotic resistance genes (ARGs) in wastewater has been less studied in wastewater treatment plants (WWTPs), making it difficult to assess ARGs' spreading risk comprehensively. Therefore, this study investigated the distribution and reduction of ARGs in the main process (Anaerobic-Anoxic-Oxic with Membrane Bio-Reactor (A2/O + MBR), Oxidation Ditch with sedimentation (OD), and Cyclic Activated Sludge System (CASS) with sedimentation) and disinfection process (Ultra-violet and Chlorination) of full-scale WWTPs. The wastewater was sampled before and after the different main process and disinfection process; then, the diversity and abundance of ARGs and mobile genetic genes (MGEs, helping the horizontal transfer of ARGs) in wastewater of different treatment stages were determined by a real-time high-throughput quantitative PCR (HT-qPCR) system. It was found that similar influents would result in similar ARGs in wastewater samples, independent of the treatment processes used. The main process could effectively reduce the abundance of ARGs and MGEs by 1.80-2.12 and 1.46-2.18 logarithm units, respectively. The main factors affecting ARGs were mainly wastewater quality index, especially COD, and MGEs like transposase and insertion sequences which were significantly associated with 66 and 48 subtypes of ARGs, respectively. Moreover, disinfection was more effective than the main process in inactivating antibiotic resistance bacteria (ARB), and the removal rate of ARB by disinfection reached 43.53 %-100 %. However, there are still risks of ARB regeneration (up to 4.22 log units) in the effluent of WWTPs. In the future, nutrient removal and disinfection process improvement is necessary to benefit ARG and ARB removal.

Mixed chlorine/chloramines in disinfected water and drinking water distribution systems (DWDSs): A critical review

Mixed chlorine/chloramines are commonly occurring in real drinking water distribution systems (DWDSs) but often overlooked. This review provides a comprehensive overview of the occurrences, characteristics, analysis methods, and control strategies of mixed chlorine/chloramines in DWDSs. The characteristics of mixed chlorine/chloramine species are summarized for treated water in drinking water treatment plants (DWTPs), secondary disinfection facilities, and DWDSs where different disinfectants could be blended. The key to differentiating and quantifying mixed chlorine/chloramine species is to separate organic chloramines (OCs) from di/tri-chloramines and overcome certain interferences. The complex interactions between water matrixes and chlorine/chloramine species could accelerate pipeline corrosions, enhance emerging disinfection by-products risks, lead to off-flavors in drinking water, and induce bio-instability issues (such as nitrification, microorganism regrowth, and promotion of horizontal gene-transfers). Three promising strategies for alleviating mixed chlorine/chloramine species are recommended, which include (i) removing precursors intensively and reconditioning the treated water, (ii) combining UV irradiation to eliminate undesired chlorine/chloramines species, and (iii) strengthening monitoring, operation, and maintenance management of DWDSs. Finally, the challenges for gaining insights into the mechanisms of mixed chlorine/chloramine species conversion are discussed and promising research directions are proposed.

Insight into the responses of antibiotic resistance genes in microplastic biofilms to zinc oxide nanoparticles and zinc ions pressures in landfill leachate

Microplastic (MP) biofilms are hotspots of antibiotic resistance genes (ARGs) in landfill environment. MP biofilms in landfill leachate coexist with heavy metals and metallic nanoparticles (NPs) that considered to be the selective agents of ARGs. However, the effects of these selective pressures on ARGs in MP biofilms and their differences in MP-surrounding leachate have not been well understood. Herein, the changes of ARG abundances in MP biofilms and corresponding leachate under zinc oxide (ZnO) NPs and zinc ion (Zn2+) pressures were comparatively analyzed. The presence of ZnO NPs and Zn2+ promoted the enrichment of ARGs in MP biofilms, and the enrichment was more pronounced in ZnO NPs groups. ZnO NPs and especially Zn2+ mainly decreased the abundances of ARGs in leachate. The increase of integron abundances and reactive oxygen species production in MP biofilms implied the enhanced potential for horizontal transfer of ARGs under ZnO NPs and Zn2+ pressures. Meanwhile, the co-occurrence pattern between ARGs and bacterial genera in MP biofilms with more diverse potential ARG hosts was more complex than in leachate, and the enrichment of ARG-hosting bacteria in MP biofilms under ZnO NPs and Zn2+ pressures supported the enrichment of ARGs.

Chlorine disinfection modifies the microbiome, resistome and mobilome of hospital wastewater - A nanopore long-read metagenomic approach

The aim of the present study was to analyze changes in the microbiome, resistome, and mobilome of hospital wastewater (HWW) induced by disinfection with chlorine compounds. Changes in bacterial communities and specific antibiotic resistance genes (ARGs) in HWW were determined with the use of a nanopore long-read metagenomic approach. The main hosts of ARGs in HWW were identified, and the mobility of resistance mechanisms was analyzed. Special attention was paid to the prevalence of critical-priority pathogens in the HWW microbiome, which pose the greatest threat to human health. The results of this study indicate that chlorine disinfection of HWW can induce significant changes in the structure of the total bacterial population and antibiotic resistant bacteria (ARB) communities, and that it can modify the resistome and mobilome of HWW. Disinfection favored the selection of ARGs, decreased their prevalence in HWW, while increasing their diversity. The mobility of the HWW resistome increased after disinfection. Disinfection led to the emergence of new drug resistance mechanisms in previously sensitive bacterial taxa. In conclusion, this study demonstrated that HWW disinfected with low (sublethal) concentrations of free chlorine significantly contributes to the mobility and transfer of drug resistance mechanisms (including critical mechanisms) between bacteria (including pathogens).