Contribution of antibiotics to the fate of antibiotic resistance genes in anaerobic treatment processes of swine wastewater: A review

A comprehensive review of antibiotic resistance gene contamination in agriculture: Challenges and AI-driven solutions

Since their discovery, the prolonged and widespread use of antibiotics in veterinary and agricultural production has led to numerous problems, particularly the emergence and spread of antibiotic-resistant bacteria (ARB). In addition, other anthropogenic factors accelerate the horizontal transfer of antibiotic resistance genes (ARGs) and amplify their impact. In agricultural environments, animals, manure, and wastewater are the vectors of ARGs that facilitate their spread to the environment and humans via animal products, water, and other environmental pathways. Therefore, this review comprehensively analyzed the current status, removal methods, and future directions of ARGs on farms. This article 1) investigates the origins of ARGs on farms, the pathways and mechanisms of their spread to surrounding environments, and various strategies to mitigate their spread; 2) determines the multiple factors influencing the abundance of ARGs on farms, the pathways through which ARGs spread from farms to the environment, and the effects and mechanisms of non-antibiotic factors on the spread of ARGs; 3) explores methods for controlling ARGs in farm wastes; and 4) provides a comprehensive summary and integration of research across various fields, proposing that in modern smart farms, emerging technologies can be integrated through artificial intelligence to control or even eliminate ARGs. Moreover, challenges and future research directions for controlling ARGs on farms are suggested.

Antibiotic resistance genes risks in relation to host pathogenicity and mobility in a typical hospital wastewater treatment process

Hospital wastewaters (HWWs) serve as critical reservoirs for disseminating antibiotic resistance genes (ARGs) and antibiotic resistant bacteria (ARB). However, the dynamics and noteworthy shifts of ARGs and their associated pathogenicity, mobility, and resistome risks during HWWs treatment processes remain poorly understood. Utilizing metagenomic sequencing and assembly, we identified 817 ARG subtypes conferring resistance to 20 classes of antibiotics across 18 HWW samples from influent to effluent. Genes encoding resistance to multidrug, aminoglycoside and beta_lactam were the most prevalent ARG types, reflecting patterns observed in clinical settings. On-site treatment efforts decreased the relative abundance of ARGs by 77.4% from influent to secondary sedimentation, whereas chlorine disinfection significantly increased their abundance in the final effluent. Deterministic processes primarily drove the taxonomic assembly, with Proteobacteria being the most abundant phylum and serving as the primary host for 15 ARG types. Contig-based analysis further revealed 114 pathogenic ARB, with Escherichia coli, Pseudomonas alcaligenes, and Pseudomonas aeruginosa exhibiting multidrug-resistant. The contributions of host bacteria and pathogenic ARB varied throughout wastewater treatment. In addition, 7.10%-31.0 % ARGs were flanked by mobile genetic elements (MGEs), predominantly mediated by transposase (74.1%). Notably, tnpA exhibited the highest potential for ARG dissemination, frequently co-occurring with beta-lactam resistance genes (35.2%). Considering ARG profiles, pathogenic hosts, and transferability, raw influent exhibited the highest antibiotic resistome risk index (ARRI), followed by the final effluent. Chlorine disinfection exacerbated resistome risks by inducing potential pathogenic ARB and mobile ARGs, posing threats to the receiving environment. This study delineates ARG occurrence patterns, highlights mechanisms of ARG carriage and horizontal gene transfer, and provides insights for assessing resistance risks and prioritizing interventions in clinical settings.

An Antibiotic-Degrading Engineered Biofilm Platform to Combat Environmental Antibiotic Resistance

The presence of antibiotics in natural water bodies is a growing problem regarding the occurrence of antibiotic resistance among various species. This is mainly caused by the excessive use of medical and veterinary antibiotics as well as the lack of effective treatment processes for eliminating residual antibiotics from wastewaters. In this study, we introduce a genetically engineered biomaterial as a solution for the effective degradation of one of the dominantly found antibiotics in natural water bodies. Our biomaterial harnesses laccase-type enzymes, which are known to attack specific types of antibiotics, i.e., fluoroquinolone-type synthetic antibiotics, and as a result degradation occurs. The engineered biomaterial is built using Escherichia coli biofilm protein CsgA as a scaffold, which is fused separately to two different laccase enzymes with the SpyTag-SpyCatcher peptide-protein duo. The designed biofilm materials were successful in degrading ciprofloxacin, as demonstrated with the data obtained from mass spectrometry analysis and cell viability assays.

Effects of Hydrothermal Pretreatment and Anaerobic Digestion of Pig Manure on the Antibiotic Removal and Methane Production

Whether advanced biological waste treatment technologies, such as hydrothermal pretreatment (HTP) integrated anaerobic digestion (AD), could enhance the removal of different antibiotics remains unclear. This study investigated the outcome of antibiotics and methane productivity during pig manure treatment via HTP, AD, and HTP + AD. Results showed improved removal efficiency of sulfadiazine (SDZ), oxytetracycline (OTC), and enrofloxacin (ENR) with increased HTP temperatures (70, 90, 120, 150, and 170 °C). OTC achieved the highest removal efficiency of 86.8% at 170 °C because of its high sensitivity to heat treatment. For AD, SDZ exhibited resistance with a removal efficiency of 52.8%. However, OTC and ENR could be removed completely within 30 days. When HTP was used prior to AD, OTC and ENR could achieve complete removal. However, residual SDZ levels reduced to 20% and 16% at 150 and 170 °C, respectively. The methanogenic potential showed an overall upward trend as the HTP temperature increased. Microbial analysis revealed the antibiotics-induced enrichment of specific microorganisms during AD. Firmicutes were the dominant bacterial phylum, with their abundance positively correlated with the addition of antibiotics. Methanobacterium and Methanosarcina emerged as the dominant archaea that drove methane production during AD. Thus, HTP can be a potential pretreatment before AD to reduce antibiotic-related risks in manure waste handling.

Fate of antibiotic resistance genes and roles of biochar in wastewater treated with biochar/persulfate

Advanced oxidation processes based on persulfate activation by biochar have been widely used to remove antibiotics and antibiotic resistance genes (ARGs) from wastewater. In this study, we used a common continuous fixed-bed reactor based on a biochar/persulfate system to treat wastewater. The average apparent ARG-removal efficiency was 82.38% in the biochar/persulfate reactor. The results of continuous reactor activity suggested the presence of ARG residues in the biochar (the abundance of ARG in the biochar increased 103-fold) and unstable removal of extracellular ARGs, raising concerns about a potential environmental burden. Kinetic experiments showed that the absolute abundance of intracellular ARGs (iARGs) rapidly decreased 98.3% within 30 min, but extracellular ARGs (eARGs) correspondingly increased 15-fold, suggesting that persulfate broke bacterial cells open and quickly released iARGs as eARGs. Moreover, the proportions of the three types of ARGs showed that ARG removal was attributed to about 70% degradation and 30% adsorption by the biochar/persulfate reactor. Further analysis revealed that biochar acts as a special shelter for ARGs. Release experiment of used biochar indicated that nearly half of absorbed ARGs could be released into new environment and causing potential risk. Overall, our findings provide a fundamental understanding of the fate of ARGs during treatment of antibiotic-contaminated wastewater and new insights into the multiple roles of biochar, which can potentially represent an additional burden on ecosystems and human health.

The contribution of swine wastewater on environmental pathogens and antibiotic resistance genes: Antibiotic residues and beyond

Swine wastewater application can introduce antibiotics, antibiotic resistance genes (ARGs) into environments. Herein, the full-scale transmission of antibiotics, ARGs and their potential carriers from an intensive swine feedlot to its surroundings were explored. Results showed that lincomycin and doxycycline hydrochloride were dominant antibiotics in this ecosystem. Lincomycin concentration were strongly associated with soil bacterial communities. According to the risk quotient (RQ), lincomycin was identified as posing higher ecological risk in aquatic environments. ARGs and mobile genetic elements (MGEs) abundance in wastewater were reduced after anaerobic treatment. Notably, ARGs composition of environmental samples were clustered into two groups based on if they were directly affected by the wastewater. However, there were no remarkable difference of ARGs abundance among environmental samples. The total abundance of ARGs was positively related to that of MGEs. Pathogens Escherichia coli and Enterococcus revealed strong connection with qnrS, tet and sul. Overall, this study highlights the importance of responsible antibiotics use in livestock production and appropriate treatment technology before agricultural application and discharge.

From disinfection to pathogenicity: Occurrence, resistome risks and assembly mechanism of biocide and metal resistance genes in hospital wastewaters

Hospital wastewaters (HWWs) represent critical reservoir for the accumulation and propagation of resistance genes. However, studies on biocide and metal resistance genes (BMRGs) and their associated resistome risks and driving mechanisms in HWWs are still in their infancy. Here, metagenomic assembly was firstly used to investigate host pathogenicity and transferability profiles of BMGRs in a typical HWWs system. As a result, genes conferring resistance to Ethidium Bromide, Benzylkonium Chloride, and Cetylpyridinium Chloride dominated biocide resistance genes (BRGs), whereas Cu resistance gene was the largest contributor of metal resistance genes (MRGs). Most BMRGs experienced significant reduction from anoxic-aerobic treatment to sedimentation stages but exhibited enrichment after chlorine disinfection. Network analysis indicated intense interactions between BMRGs and virulence factors (VFs). Polar_flagella, belonging to the adherence was identified to play important role in the network. Contig-based analysis further revealed noteworthy shifts in host associations along the treatment processes, with Pseudomonadota emerging as the primary carrier, hosting 91.1% and 85.3% of the BRGs and MRGs. A total of 199 opportunistic pathogens were identified to carry 285 BMRG subtypes, which mainly included Pseudomonas alcaligenes, Pseudomonas lundensis, and Escherichia coli. Notably, ruvB conferring resistance to Cr, Cetylpyridinium Chloride, and Dodine were characterized with the highest frequency carried by pathogens. Diverse co-occurrence patterns between BMRGs and mobile genetic elements (MGEs) were found from the raw influent to final effluent. Overall, 10.5% BRGs and 8.84% MRGs were mobile and among the 4 MGEs, transposase exhibited the greatest potential for the BMRGs dissemination. Furthermore, deterministic processes played a dominant role in bacterial communities and BMRGs assembly in HWWs. Bacterial communities contributed more than MGEs in shaping the resistome. Taken together, this work demonstrated widespread BMRGs pollution throughout the HWWs treatment system, emphasizing the potential for informing resistome risk and ecological mechanism in medical practice.

Microbial response and recovery strategy of the anammox process under ciprofloxacin stress from pure strain and consortia perspectives

Ciprofloxacin (CIP) poses a high risk of resistance development in water environments. Therefore, comprehensive effects and recovery strategies of CIP in anaerobic ammonia oxidation (anammox) process were systematically elucidated from consortia and pure strains perspectives. The anammox consortia was not significantly affected by the stress of 10 mg L-1 CIP, while the higher concentration (20 mg L-1) of CIP caused a dramatic reduction in the nitrogen removal performance of anammox system. Simultaneously, the abundances of dominant functional bacteria and corresponding genes also significantly decreased. Such inhibition could not be mitigated by the recovery strategy of adding hydrazine and hydroxylamine. Reducing nitrogen load rate from 5.1 to 1.4 kg N m-3 d-1 promoted the restoration of three reactors. In addition, the robustness and recovery of anammox systems was evaluated using starvation and shock strategies. Simultaneously, antibiotic resistance genes and key metabolic pathways of anammox consortia were upregulated, such as carbohydrate and energy metabolisms. In addition, 11 pure stains were isolated from the anammox system and identified through phylogenetic analysis, 40 % of which showed multidrug resistance, especially Pseudomonas. These findings provide deep insights into the responding mechanism of anammox consortia to CIP stress and promote the application of anammox process for treating wastewater containing antibiotics.

An evaluation of conventional and nature-based technologies for controlling antibiotic-resistant bacteria and antibiotic-resistant genes in wastewater treatment plants

Antibiotic resistance is a globally recognized health concern which leads to longer hospital stays, increased morbidity, increased mortality, and higher medical costs. Understanding how antibiotic resistance persists and exchanges in environmental systems like soil, water, and wastewater are critically important for understanding the emergence of pathogens with new resistance profiles and the subsequent exposure of people who indirectly/directly come in contact with these pathogens. There are concerns about the widespread application of prophylactic antibiotics in the clinical and agriculture sectors, as well as chemicals/detergents used in food and manufacturing industries, especially the quaternary ammonium compounds which have been found responsible for the generation of resistant genes in water and soil. The rates of horizontal gene transfer increase where there is a lack of proper water/wastewater infrastructure, high antibiotic manufacturing industries, or endpoint users - such as hospitals and intensive agriculture. Conventional wastewater treatment technologies are often inefficient in the reduction of ARB/ARGs and provide the perfect combination of conditions for the development of antibiotic resistance. The wastewater discharged from municipal facilities may therefore be enriched with bacterial communities/pathogens and provide a suitable environment (due to the presence of nutrients and other pollutants) to enhance the transfer of antibiotic resistance. However, facilities with tertiary treatment (either traditional/emerging technologies) provide higher rates of reduction. This review provides a synthesis of the current understanding of wastewater treatment and antibiotic resistance, examining the drivers that may accelerate their possible transmission to a different environment, and highlighting the need for tertiary technologies used in treatment plants for the reduction of resistant bacteria/genes.

Bibliometric analysis of global performance and trends of research on combined sewer overflows (CSOs) from 1990 to 2022

Combined sewer overflows (CSOs) are one of the main sources of pollution in urban water systems and significantly impede the restoration of water body functionalities within urban rivers and lakes. To understand the research and frontier trends of CSOs comprehensively and systematically, a visual statistical analysis of the literature related to CSOs in the Web of Science core database from 1990 to 2022 was conducted using the bibliometric method using HistCite Pro and VOSviewer. The results reveal a total of 1,209 pertinent publications related to CSOs from 1990 to 2022, and the quantity of CSOs-related publications indicated an increasing trend. Investigations of the distribution and fate of typical pollutants in CSOs and their ecological effects on receiving waters and studies on pollution control technologies (source reduction, process control, and end-of-pipe treatment) are the current focus of CSOs research. CSOs pollution control technologies based on source reduction and the monitoring and control of emerging contaminants are at the forefront of scientific investigations on CSOs. This study systematically and comprehensively summarized current research topics and future research directions of CSOs, thus providing a reference for CSOs control and water environment management research.

Biodegradation strategies of veterinary medicines in the environment: Enzymatic degradation

One Health closely integrates healthy farming, human medicine, and environmental ecology. Due to the ecotoxicity and risk of transmission of drug resistance, veterinary medicines (VMs) are regarded as emerging environmental pollutants. To reduce or mitigate the environmental risk of VMs, developing friendly, safe, and effective removal technologies is an important means of environmental remediation for VMs. Many previous studies have proved that biodegradation has significant advantages in removing VMs, and biodegradation based on enzyme catalysis presents higher operability and specificity. This review focused on biodegradation strategies of environmental pollutants and reviewed the enzymatic degradation of VMs including antimicrobial drugs, insecticides, and disinfectants. We reviewed the sources and catalytic mechanisms of peroxidase, laccase, and organophosphorus hydrolases, and summarized the latest research status of immobilization methods and bioengineering techniques in improving the performance of degrading enzymes. The mechanism of enzymatic degradation for VMs was elucidated in the current research. Suggestions and prospects for researching and developing enzymatic degradation of VMs were also put forward. This review will offer new ideas for the biodegradation of VMs and have a guide significance for the risk mitigation and detoxification of VMs in the environment.

Pharmaceutically active micropollutants: origin, hazards and removal

Pharmaceuticals, recognized for their life-saving potential, have emerged as a concerning class of micropollutants in the environment. Even at minute concentrations, chronic exposure poses a significant threat to ecosystems. Various pharmaceutically active micropollutants (PhAMP), including antibiotics, analgesics, and hormones, have been detected in underground waters, surface waters, seawater, sewage treatment plants, soils, and activated sludges due to the absence of standardized regulations on pharmaceutical discharge. Prolonged exposureof hospital waste and sewage treatment facilities is linked to the presence of antibiotic-resistant bacteria. Conventional water treatment methods prove ineffective, prompting the use of alternative techniques like photolysis, reverse osmosis, UV-degradation, bio-degradation, and nano-filtration. However, commercial implementation faces challenges such as incomplete removal, toxic sludge generation, high costs, and the need for skilled personnel. Research gaps include the need to comprehensively identify and understand various types of pharmaceutically active micropollutants, investigate their long-term ecological impact, develop more sensitive monitoring techniques, and explore integrated treatment approaches. Additionally, there is a gap in understanding the socio-economic implications of pharmaceutical pollution and the efficacy of public awareness campaigns. Future research should delve into alternative strategies like phagotherapy, vaccines, and natural substance substitutes to address the escalating threat of pharmaceutical pollution.

Performance of sewage sludge treatment for the removal of antibiotic resistance genes: Status and prospects

Wastewater treatment plants (WWTPs) receive wastewater containing antibiotic resistant bacteria (ARB) and antibiotic resistant genes (ARGs), which are predominant contributors to environmental pollution in water and soil. Of these sources, sludge is a more significant contributor than effluent. Knowing how sludge treatment affects the fate of ARGs is vital for managing the risk of these genes in both human and natural environments. This review therefore discusses the sources and transmission of ARGs in the environment and highlights the risks of ARGs in sludge. The effects of co-existing constituents (heavy metals, microplastics, etc.) on sludge and ARGs during treatment are collated to highlight the difficulty of treating sludge with complex constituents in ARGs. The effects of various sludge treatment methods on the abundances of ARGs in sludge and in soil from land application of treated sludge are discussed, pointing out that the choice of sludge treatment method should take into account various potential factors, such as soil and soil biology in subsequent land application. This review offers significant insights and explores the abundances of ARGs throughout the process of sludge treatment and disposal. Unintentional addition of antibiotic residues, heavy metals, microplastics and organic matter in sludge could significantly increase the abundance and reduce the removal efficiency of ARGs during treatment, which undoubtedly adds a barrier to the removal of ARGs from sludge treatment. The complexity of the sludge composition and the diversities of ARGs have led to the fact that no effective sludge treatment method has so far been able to completely eliminate the ecological risk of ARGs. In order to reduce risks resulting by transmission of ARGs, technical and management measures need to be implemented.

Distribution and major driving elements of antibiotic resistance genes in the soil-vegetable system under microplastic stress

Microplastics (MPs) and antibiotic resistance genes (ARGs) are both enriched in soil-vegetable systems as a consequence of the prolonged use of agricultural mulches. MPs can form unique bacterial communities and provide potential hosts for ARGs. Therefore, MPs stress may promote the spread of ARGs from soil to crops. Increasing ARGs pollution in soil-vegetable system. In our research, we investigated the distribution and major driving elements of antibiotic resistance genes in the soil-vegetable system under microplastic stress. The results showed that MPs treatment decreased the relative abundance of ARGs in non-rhizosphere soil. High concentrations of MPs promoted the enrichment of tetracycline antibiotic resistance genes in rhizosphere soil. MPs treatment promoted the enrichment of ARGs and mobile genetic elements (MGEs) in lettuce tissues, and the overall abundance of ARGs in root after 0.5 %, 1 %, and 2 % (w/w, dry weight) polyethylene (PE) administration was considerably higher compared to that in the untreated group (p < 0.05). At the same time, high PE concentrations promoted the spread of sulfa ARGs from root to leaf. MPs also impacted the bacterial communities in the soil-plant system, and the changes in ARGs as well as MGEs in each part of the soil-vegetable system were significantly correlated with the bacterial diversity index (p < 0.05). Correlation analysis and network analysis showed that bacterial communities and MGEs were the main drivers of ARGs variation in soil-lettuce systems.

Sub-MIC antibiotics influence the microbiome, resistome and structure of riverine biofilm communities

The effects of sub-minimum inhibitory concentrations (sub-MICs) of antibiotics on aquatic environments is not yet fully understood. Here, we explore these effects by employing a replicated microcosm system fed with river water where biofilm communities were continuously exposed over an eight-week period to sub-MIC exposure (1/10, 1/50, and 1/100 MIC) to a mix of common antibiotics (ciprofloxacin, streptomycin, and oxytetracycline). Biofilms were examined using a structure-function approach entailing microscopy and metagenomic techniques, revealing details on the microbiome, resistome, virulome, and functional prediction. A comparison of three commonly used microbiome and resistome databases was also performed. Differences in biofilm architecture were observed between sub-MIC antibiotic treatments, with an overall reduction of extracellular polymeric substances and autotroph (algal and cyanobacteria) and protozoan biomass, particularly at the 1/10 sub-MIC condition. While metagenomic analyses demonstrated that microbial diversity was lowest at the sub-MIC 1/10 antibiotic treatment, resistome diversity was highest at sub-MIC 1/50. This study also notes the importance of benchmarking analysis tools and careful selection of reference databases, given the disparity in detected antimicrobial resistance genes (ARGs) identity and abundance across methods. Ultimately, the most detected ARGs in sub-MICs exposed biofilms were those that conferred resistance to aminoglycosides, tetracyclines, β-lactams, sulfonamides, and trimethoprim. Co-occurrence of microbiome and resistome features consistently showed a relationship between Proteobacteria genera and aminoglycoside ARGs. Our results support the hypothesis that constant exposure to sub-MICs antibiotics facilitate the transmission and promote prevalence of antibiotic resistance in riverine biofilms communities, and additionally shift overall microbial community metabolic function.

Differential dose-response patterns of intracellular and extracellular antibiotic resistance genes under sub-lethal antibiotic exposure

Although antibiotics are one of the most significant factors contributing to the propagation of antibiotic resistance genes (ARGs), studies on the dose-response relationship at sub-lethal concentrations of antibiotics remain scarce, despite their importance for assessing the risks of antibiotics in the environment. In this study, we constructed a series of microcosms to investigate the propagation of intracellular (iARGs) and extracellular (eARGs) ARGs in both water and biofilms when exposed to antibiotics at various concentrations (1-100 μg/L) and frequencies. Results showed that eARGs were more abundant than iARGs in water, while iARGs were the dominant ARGs form in biofilms. eARGs showed differentiated dose-response relationships from iARGs. The abundance of iARGs increased with the concentration of antibiotics as enhanced selective pressure overcame the metabolic burden of antibiotic-resistant bacteria carrying ARGs. However, the abundance of eARGs decreased with increasing antibiotic concentrations because less ARGs were secreted from bacterial hosts at higher concentrations (100 μg/L). Furthermore, combined exposure to two antibiotics (tetracycline & imipenem) showed a synergistic effect on the propagation of iARGs, but an antagonistic effect on the propagation of eARGs compared to exposure to a single antibiotic. When exposed to antibiotic at a fixed total dose, one-time dosing (1 time/10 d) favored the propagation of iARGs, while fractional dosing (5 times /10 d) favored the propagation of eARGs. This study sheds light on the propagation of antibiotic resistance in the environment and can help in assessing the risks associated with the use of antibiotics.

A review of the impact of conductive materials on antibiotic resistance genes during the anaerobic digestion of sewage sludge and animal manure

The urgent need to reduce the environmental burden of antibiotic resistance genes (ARGs) has become even more apparent as concerted efforts are made globally to tackle the dissemination of antimicrobial resistance. Concerning levels of ARGs abound in sewage sludge and animal manure, and their inadequate attenuation during conventional anaerobic digestion (AD) compromises the safety of the digestate, a nutrient-rich by-product of AD commonly recycled to agricultural land for improvement of soil quality. Exogenous ARGs introduced into the natural environment via the land application of digestate can be transferred from innocuous environmental bacteria to clinically relevant bacteria by horizontal gene transfer (HGT) and may eventually reach humans through food, water, and air. This review, therefore, discusses the prospects of using carbon- and iron-based conductive materials (CMs) as additives to mitigate the proliferation of ARGs during the AD of sewage sludge and animal manure. The review spotlights the core mechanisms underpinning the influence of CMs on the resistome profile, the steps to maximize ARG attenuation using CMs, and the current knowledge gaps. Data and information gathered indicate that CMs can profoundly reduce the abundance of ARGs in the digestate by easing selective pressure on ARGs, altering microbial community structure, and diminishing HGT.

Removal of nutrients and veterinary antibiotics from manure-free piggery wastewater in a packed-bed A/O process at normal atmospheric temperature

A packed-bed anaerobic-aerobic reactor (PBAOR) with two anaerobic and two aerobic compartments was constructed to treat manure-free piggery wastewater which was characterized by high ammonium (NH4⁺-N) and low ratio of chemical oxygen demand (COD) to total nitrogen (TN). Performed for 60 days at the normal atmospheric temperature of 25 °C with a constant hydraulic retention time of 32 h and reflux ratio of 2.0, a stable state in pollutants removal was obtained in the PBAOR. Within the next routine operation process, the removal of COD, NH4⁺-N and TN was above 85.7%, 98.2% and 85.8%, with a residual less than 81.7, 7.2 and 39.9 mg L^-1 in effluent, respectively. Twelve veterinary antibiotics classified into tetracyclines (TCs), sulphonamides (SAs) and fluoroquinolones (FQs) were detected from the piggery wastewater. The PBAOR was effective in removing TCs and SAs with an average removal of 74.8% and 93.3%, respectively, but presented a negative removal for FQs. Most COD in the piggery wastewater was mainly removed in the first two anaerobic compartments along with an obvious removal of TCs and SAs, while the TN were mainly removed in the last two aerobic compartments with the negative removal of FQs.

Effects of functional modules and bacterial clusters response on transmission performance of antibiotic resistance genes under antibiotic stress during anaerobic digestion of livestock wastewater

The formation and transmission of antibiotic resistance genes (ARGs) have attracted increasing attention. It is unclear whether the internal mechanisms by which antibiotics affect horizontal gene transfer (HGT) of ARGs during anaerobic digestion (AD) were influenced by dose and type. We investigated the effects of two major antibiotics (oxytetracycline, OTC, and sulfamethoxazole, SMX) on ARGs during AD according to antibiotic concentration in livestock wastewater influent. The low-dose antibiotic (0.5 mg/L) increased ROS and SOS responses, promoting the formation of ARGs. Meanwhile, low-dose antibiotics could also promote the spread of ARGs by promoting pili, communication responses, and the type IV secretion system (T4SS). However, different types and doses of antibiotics would lead to changes in the above functional modules and then affect the enrichment of ARGs. With the increasing dose of SMX, the advantages of pili and communication responses would gradually change. In the OTC system, low-dose has the strongest promoting ability in both pili and communication responses. Similarly, an increase in the dose of SMX would change T4SS from facilitation to inhibition, while OTC completely inhibits T4SS. Microbial and network analysis also revealed that low-dose antibiotics were more favorable for the growth of host bacteria.

Removal of antibiotic resistance genes during livestock wastewater treatment processes: Review and prospects

Antibiotic resistance genes (ARGs) are emerging pollutants that have received extensive attention. Many different types of ARGs exist in livestock wastewater. If not effectively treated, they can threaten animal production, public health and the ecological safety of the surrounding environment. To address the high risk of livestock wastewater contamination by ARGs, the effects of different wastewater treatment processes on ARGs and their influencing factors and mechanisms are reviewed herein. Additionally, the current problems associated with removal of ARGs are discussed, and future research is proposed.

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.

A Study of the Degradation of LEV by Transparent PVA/NCD-TiO2 Nanocomposite Films with Enhanced Visible-Light Photocatalytic Activity

In recent years, antibiotics (such as levofloxacin (LEV)) have been detected widely in the environment. Semiconductor photocatalysis has been recognized as a promising technology for removing pollutants in the environment. In this work, nitrogen and carbon codoped titanium dioxide nano-catalyst (NCD-TiO2) was immobilized in polyvinyl alcohol (PVA) matrix to form PVA/NCD-TiO2 films through solution casting and thermal treatment, which exhibited good photocatalytic efficiency for LEV degradation. The results showed that about 42% LEV can be degraded after 2 h in the presence of PVA/NCD-TiO2 nanocomposite film (the weight ratio of NCD-TiO2 to PVA is 8% and thermal treatment is 120 °C) under visible light. Moreover, possible pathways of photocatalytic degradation of LEV according to the detected intermediates are proposed, which provide insight into the degradation mechanism of LEV by using PVA/NCD-TiO2 photocatalytic films. Finally, the synthesized PVA/NCD-TiO2 films exhibited excellent reusability and stability in photocatalysis. This work provides fundamental support for the design of a high-stability, excellent photocatalyst for practical application.

Effects of composting on the fate of doxycycline, microbial community, and antibiotic resistance genes in swine manure and broiler manure

Aerobic composting is an economical and effective technology that is widely used to treat animal manure. To study the fate of doxycycline (DOX), the microbial community, and antibiotic resistance genes (ARGs) during composting, aerobic composting of broiler manure and swine manure was carried out under natural environmental conditions. Aerobic composting effectively removed DOX (with a removal rate > 97%) and most ARGs from animal manure. The microbial diversity and the numbers of ARGs were higher in composted swine manure compared with composted broiler manure. The microbial community structure changed during composting, and the dominant phyla of broiler manure and swine manure changed from Firmicutes to Bacteroidetes and Proteobacteria, respectively. DOX changed the structure and relative abundance of the microbial community during composting, and the relative abundance of multidrug resistance genes and mobile genetic elements (MGEs) increased, which might lead to the risk of transmission of resistance in the environment. The C / N ratio, DOX concentration, Firmicutes, intl1, and intl2 were the key factors driving the change in ARGs during composting. These results help to reveal the effects of DOX on microbial communities, ARGs, and MGEs during composting and clarify the possible ways to reduce the risk of resistance gene transmission in the environment.

Experimental Data and Modeling the Adsorption-Desorption and Mobility Behavior of Ciprofloxacin in Sandy Silt Soil

The improved understanding of the behavior of antibiotics in soil is of great importance due to their environmental hazard and frequent detection. In this work, the adsorption-desorption and mobility behaviors of ciprofloxacin in sandy silt soil, affecting the fate of ciprofloxacin in the environment, were studied by a series of batch tests and column tests. In batch tests, the effects of contact time, initial ciprofloxacin concentration, sandy silt soil dosage, solution pH, and ionic strength on ciprofloxacin adsorption and desorption in sandy silt soil were considered. Adsorption results were satisfactorily modeled, with good fittings to the pseudo-second-order model (R2 > 0.999) and Langmuir model (R2 > 0.991), with the value for Langmuir’s maximum adsorption capacity (qm) 5.50 mg g−1. Ciprofloxacin adsorption decreased sharply by increasing the pH from 7.0 to 10.0 and the ionic strength from 0.01 to 0.2 mol L−1 CaCl2. Comparatively, ciprofloxacin was more readily desorbed from sandy silt soil at alkaline and high ionic strength conditions. Breakthrough curves of ciprofloxacin obtained from the column experiments were described by the two-site model, Thomas model, and Yan mode. Of these models, the two-site model was the most suitable to describe the mobility of ciprofloxacin. The retardation factor (R) obtained in the two-site model was 345, suggesting strong adsorption affinity with ciprofloxacin on the sandy silt soil surface. The results from the Thomas model suggested the extremely small external and internal diffusion resistances. The Yan model was not suitable. Cation exchange interaction, electrostatic interaction, mechanical resistance, entrapment between porous media, and gravity sedimentation were proposed to be the important adsorption mechanisms.

The reduction and fate of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in microbial fuel cell (MFC) during treatment of livestock wastewater

The fate and removal efficiency of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in livestock wastewater by microbial fuel cell (MFC) was evaluated by High-throughput quantitative PCR. The results showed that 137 ARGs and 9 MGEs were detected in untreated livestock wastewater. The ARG number of macrolide-lincosamide-streptogramin group B (MLSB), tetracycline and sulfonamide were relatively higher. Throughout the treatment process, the number and abundance of ARGs and MGEs significantly decreased. The relative abundance of tetracycline, sulfonamide and chloramphenicol resistance genes showed the most obvious decreasing trend, and the relative abundance of MGEs decreased by 75% (from 0.012 copies/16S rRNA copies to 0.003 copies/16S rRNA copies). However, the absolute abundance of beta-lactamase resistance genes slightly increased. The operation process of MFC produces selective pressure on microorganisms, and Actinobacteria were predominant and had the ability to decompose antibiotics. The COD removal rate and TN removal rate of livestock wastewater were 67.81% and 62.09%, and the maximum power density and coulomb efficiency (CE) reached 11.49% and 38.40% respectively. This study demonstrated that although the removal of COD and TN by MFC was limited, MFC was quite effective in reducing the risk of antibiotic toxicity and horizontal gene transfer.

Degradation mechanism of montmorillonite-enhanced antibiotic wastewater: performance, antibiotic resistance genes, microbial communities, and functional metabolism

The effective degradation of Sulfamethoxazole (SMX) is of great importance to alleviate environmental pollution. In this study, the degradation capacity of an ordinary sequencing batch activated sludge system (SBR) and montmorillonite (MMT) system was compared for their ability to degrade different concentrations of SMX. Compared with SBR system, the MMT system exhibited higher stability and degradation capacity. The changes in the composition of tightly bound extracellular polymeric substances (TB-EPS) were likely key to the observed stability of the system. High concentrations of SMX inhibited the degradation performance of SBR. MMT-supplemented reduced the generation of antibiotic resistance genes (ARGs). Thauera is a gene that is able to degrade SMX, and its abundance in MMT system reached 7.84%. As potential hosts of ARGs, the proportions of Paenarthrobacter and Caldilineacea were significantly correlated with sulfonamide resistance genes (sul1 and sul2). Overall, MMT-supplemented system was found to be a favorable method of treating antibiotic.

A Review of Stand-Alone and Hybrid Microbial Electrochemical Systems for Antibiotics Removal from Wastewater

The growing concern about residual antibiotics in the water environment pushes for innovative and cost-effective technologies for antibiotics removal from wastewater. In this context, various microbial electrochemical systems have been investigated as an alternative to conventional wastewater technologies that are usually ineffective for the adequate removal of antibiotics. This review article details the development of stand-alone and hybrid or integrated microbial electrochemical systems for antibiotics removal from wastewater. First, technical features, antibiotics removal efficiencies, process optimization, and technological bottlenecks of these systems are discussed. Second, a comparative summary based on the existing reports was established to provide insights into the selection between stand-alone and hybrid systems. Finally, research gaps, the relevance of recent progress in complementary areas, and future research needs have been discussed.

The fate and behavior mechanism of antibiotic resistance genes and microbial communities in anaerobic reactors treating oxytetracycline manufacturing wastewater

In this study, two parallel-operated expanded granular sludge bed (EGSB) reactors, one used to treat oxytetracycline (OTC) manufacturing wastewater with gradual increase of OTC concentration as experimental reactor and the other fed with the same wastewater without OTC as control reactor, were operated to investigate the behavior of antibiotics resistance genes (ARGs) and mobile genetic elements (MGEs) and their possible relationships with bacterial community among influent, sludge and effluent environments. Though the average absolute abundance of ARGs slightly decreased (0.26 - log), the ARGs' relative abundance normalized to 16S-rRNA gene copy numbers showed a significant upward trend in effluent (2 multiples - increase) and the absolute and relative abundances both extremely increased in anaerobic sludge, indicating that anaerobic treatment process cannot reduce ARGs efficiently, inversely can increase the risk of ARGs through the proliferation of antibiotics resistance bacteria (ARB) under the suppression of OTC. MGEs, bacterial communities and OTC concentration mainly impacted the ARGs profiles, which contributed 88.4% to the variation of ARGs. The differences and correlations of hosts in influent, effluent and sludge were further confirmed by network analysis. Overall, this study enhanced the understanding of the prevalence and transfer of ARGs in OTC production effluents during anaerobic treatment.

Advancements in detection and removal of antibiotic resistance genes in sludge digestion: A state-of-art review

Sludge from wastewater treatment plants can act as a repository and crucial environmental provider of antibiotic resistance genes (ARGs). Over the past few years, people's knowledge regarding the occurrence and removal of ARGs in sludge has broadened remarkably with advancements in molecular biological techniques. Anaerobic and aerobic digestion were found to effectively achieve sludge reduction and ARGs removal. This review summarized advanced detection and removal techniques of ARGs, in the last decade, in the sludge digestion field. The fate of ARGs due to different sludge digestion strategies (i.e., anaerobic and aerobic digestion under mesophilic or thermophilic conditions, and in combination with relevant pretreatment technologies (e.g., thermal hydrolysis pretreatment, microwave pretreatment and alkaline pretreatment) and additives (e.g., ferric chloride and zero-valent iron) were systematically summarized and compared in this review. To date, this is the first review that provides a comprehensive assessment of the state-of-the-art technologies and future recommendations.

A Review on Constructed Treatment Wetlands for Removal of Pollutants in the Agricultural Runoff

Constructed wetland (CW) is a popular sustainable best management practice for treating different wastewaters. While there are many articles on the removal of pollutants from different wastewaters, a comprehensive and critical review on the removal of pollutants other than nutrients that occur in agricultural field runoff and wastewater from animal facilities, including pesticides, insecticides, veterinary medicine, and antimicrobial-resistant genes are currently unavailable. Consequently, this paper summarized recent findings on the occurrence of such pollutants in the agricultural runoff water, their removal by different wetlands (surface flow, subsurface horizontal flow, subsurface vertical flow, and hybrid), and removal mechanisms, and analyzed the factors that affect the removal. The information is then used to highlight the current research gaps and needs for resilient and sustainable treatment systems. Factors, including contaminant property, aeration, type, and design of CWs, hydraulic parameters, substrate medium, and vegetation, impact the removal performance of the CWs. Hydraulic loading of 10–30 cm/d and hydraulic retention of 6–8 days were found to be optimal for the removal of agricultural pollutants from wetlands. The pollutants in agricultural wastewater, excluding nutrients and sediment, and their treatment utilizing different nature-based solutions, such as wetlands, are understudied, implying the need for more of such studies. This study reinforced the notion that wetlands are effective for treating agricultural wastewater (removal > 90%) but several research questions remain unanswered. More long-term research in the actual field utilizing environmentally relevant concentrations to seek actual impacts of weather, plants, substrates, hydrology, and other design parameters, such as aeration and layout of wetland cells on the removal of pollutants, are needed.

Effects of emerging pollutants on the occurrence and transfer of antibiotic resistance genes: A review

The emergence and spread of antibiotic resistance genes (ARGs) have become major concerns for both public health and environmental ecosystems. Emerging pollutants (EPs) that accumulate in environmental compartments also pose a potential risk for the enrichment of ARGs in indigenous microorganisms. This paper presents a comprehensive review of the effects and intrinsic mechanisms of EPs, including microplastics, engineered nanomaterials, disinfection byproducts, pharmaceuticals, and personal care products, on the occurrence and dissemination of ARGs. State-of-the-art methods for identifying culture-independent ARG-host interactions and monitoring horizontal gene transfer (HGT) processes in real-time are first reviewed. The contributions of EPs to the abundance and diversity of ARGs are then summarized. Finally, we discussed the underlying mechanisms related to the regulation of HGT, increased mutagenesis, and the evolution of microbial communities. Further details of three HGT (i.e., conjugation, transformation, and transduction) frequency patterns in response to various EPs are also examined. This review contemplates and reassesses the risks of ARG evolution posed by the manufacture and application of EPs.

Constructing electrostatic self-assembled ultrathin porous red 2D g-C3N4/Fe2N Schottky catalyst for high-efficiency tetracycline removal in photo-Fenton-like processes

The traditional heterogeneous photo-Fenton reaction was mainly restricted by the fewer surface-active sites, low Fe³⁺/Fe²⁺ transformation and H₂O₂ activation efficiency of catalyst. This work designed and fabricated the efficient photo-Fenton Schottky catalysts via a facile electrostatic self-assembly of metallic Fe₂N nanoparticles scattering on the surface of red g-C₃N₄ (ultrathin porous oxygen-doped 2D g-C₃N₄ nanosheets). The porous morphology and exceptional electrical structure of red g-C₃N₄ endowed more active sites and facilitated the photoexcited charge separation. Benefitting from the Schottky effect and unique dimensional coupling structure, the strong visible light absorption and fast spatial charge transfer were realized in the Schottky junction system. More strikingly, Fe₂N as an efficient co-catalyst was in favor of the trap and export of e^-, leading to the Fe³⁺/Fe²⁺ transformation and H₂O₂ activation during the photo-Fenton process. Accordingly, the as-prepared catalysts revealed outstanding activity in photo-Fenton like degradation of tetracycline (TC) although under 5 W white LED light irradiation. Furthermore, the reasonable degradation pathway of TC and corresponding toxicity of the intermediates, as well as the photo-Fenton catalytic mechanism were interpreted and discussed in detail. This study would be a great aid in the development of various Schottky catalysts for heterogeneous photo-Fenton-based environmental remediation systems.

Antibiotic residues in wastewaters from sewage treatment plants and pharmaceutical industries: Occurrence, removal and environmental impacts

Sewage treatment plants (STPs) and pharmaceutical manufactories (PMFs) are recognized as important reservoirs for aquatic pollution with antibiotics. Although the occurrence of multiple classes of antibiotics has been mostly reported for STPs and PMFs, knowledge on the effects of wastewater treatment processes on the removal of antibiotics is not well documented. In this study, wastewaters were collected from different treatment points of two STPs and two PMFs in eastern China. Thirty-seven antibiotics within the four classes of fluoroquinolones (FQs), macrolides (MACs), sulfonamides (SAs) and tetracyclines (TCs) were analyzed. Among the investigated antibiotics, 19-33 out of 37 target compounds were detected at least once in the STPs wastewaters ranging from low ng/L to approximately 12.7 μ/L. In the wastewater samples collected from PMFs, up to 34 antibiotics were present with detection frequencies up to 100%, showing generally higher concentrations (up to 19.0 μ/L) than those at the STPs. FQs and SAs were the dominant antibiotic families, which accounted for more than 90% of the total antibiotic concentration in the wastewaters. Moreover, the removal of antibiotics by anaerobic-anoxic-oxic (A²O), membrane bioreactor (MBR) and conventional activated sludge (CAS) systems was evaluated. The MBR system exhibited the best performance, mainly due to the processes of biodegradation and sorption during biological treatments. Notably, several SAs (SMP, SMZ) and FQs (CIN, ENO) antibiotics were consistently detected at concentration levels of μ/L in the effluent samples. The culturable antibiotic-resistance tests and risk assessment indicated that the antibiotic-contaminated effluents would facilitate the development of resistant bacteria and pose high toxicity to non-target organisms in the aquatic environment. Overall, the findings suggested an urgent need for improving the wastewater treatment technologies for simultaneous removal of different classes of antibiotics.

Anaerobic biodegradation of four sulfanilamide antibiotics: Kinetics, pathways and microbiological studies

Large amounts of sulfanilamide antibiotics (SAs) have been excreted into the manure. In this study, the anaerobic biodegradation of four kinds of SAs including sulfaquinoxaline (SQX), sulfamethoxazole (SMX), sulfamethoxine (SMD) and sulfathiazole (STZ) was investigated. The degradation rates of SQX and STZ decreased with the increase of the concentrations of other organics, but those of SMX and SMD were less affected. The average degradation rates of SAs were in the order of SMX >SMD ≈QX >STZ, with the best degradation rate constants of 0.30125, 0.14752, 0.16696, and 0.06577 /d, respectively. STZ had the greatest effect on the population richness of microbes, whereas SQX had the largest impact on the population diversity. The degradation rates of SAs were positively correlated with the abundances of Proteobacteria and Bacteroidetes, and negatively correlated with the abundance of Firmicutes. The common degradation pathways of SAs were S-N cleavage and substitution. The specific functional groups of SQX, SMX and SMD, including quinoxaline, isoxazole and pyrimidine rings, could be opened, but the thiazole ring of STZ was difficult to be decomposed. After the rings of the specific functional groups were opened, they would be further substituted or decomposed to be products with small molecules.

Response of antibiotic and heavy metal resistance genes to tetracyclines and copper in substrate-free hydroponic microcosms with Myriophyllum aquaticum

Constructed wetlands for antibiotics and heavy metals removal have become important reservoirs of antibiotic resistance genes (ARGs) and heavy metal resistance genes (MRGs), especially in the substrates. Here, substrate-free hydroponic microcosms of Myriophyllum aquaticum were established; tetracyclines (TCs) and Cu(II) were added to evaluate the behaviours of ARGs and MRGs in the microcosms. Several ARGs, MRGs, and mobile genetic elements (MGE) were detected in the biofilms attached to the plants, ranging from 0.5 to 2.3 × 10⁸ copies/g dry weight. ARGs and MRGs exhibited higher relative abundances in the effluent suspended solids (SS); however, their absolute amounts were much lower than those in conventionally constructed wetlands. Microcosms with TCs and Cu(II) exhibited a higher level of resistant genes than those with compound added singularly owing to co-selection pressure. The existence of TCs and copper significantly changed the microbial communities in the microcosms. The exogenous input of TC/Cu(II) and microbial community structure were the factors driving the occurrence of ARGs, whereas MRGs were more correlated with the copper addition. Thus, reducing the exogenous inputs of antibiotics /heavy metals and SS of the effluent is suggested for the mitigation of resistant genes in phytoremediation technologies working in the absence of conventional substrates.

Enrichment of antibiotic resistance genes after sheep manure aerobic heap composting

In this study, physio-chemical properties, 45 antibiotics, 6 heavy metals, 42 antibiotic resistance genes (ARGs), 3 mobile genetic elements, and the bacterial community structure were investigated to analyze the fate of ARGs during sheep manure aerobic heap composting. Results showed that sheep manure heap composting could produce mature compost. The degradation processes reduced the total antibiotics content by 85%. The abundance of ARGs and mobile genetic elements (MGEs) were enriched 9-fold, with the major increases to sul and tet genes (sulI, sulII, tetQ, and tetX). Tetracycline and sulfonamide resistance genes were the most abundant ARGs after composting (more than 88% of all genes). The genes tetA, tetX and sulI were related to the most diverse bacteria that were most able to proliferate during heap composting. Therefore, sulI and tetX are the major ARGs to be controlled, and Actinobacteria and Bacteroidetes may be the major host bacteria.

Profiles of bacteria/phage-comediated ARGs in pig farm wastewater treatment plants in China: Association with mobile genetic elements, bacterial communities and environmental factors

In this study, the profiles of bacteria/phage-comediated antibiotic resistance genes (b/pARGs) were monitored in water samples collected from 45 pig farm wastewater treatment plants (WWTPs) in seven different regions of China. We found that 8 major types and 112 subtypes of b/pARGs were detected in all the water samples, and the detected number ranged from 53 to 92. The absolute abundances of bARGs and pARGs in the influent were as high as 10⁹ copies/mL and 10⁶ copies/mL, respectively. Anaerobic anoxic/oxic (AAO) and anaerobic short-cut nitrification/denitrification (ASND) treatment plants can effectively reduce the absolute abundance and amount of b/pARGs. Anaerobic treatment plants cannot reduce the absolute abundance of pARGs, and even increase the amount of pARGs. Mobile genetic elements (MGEs), bacterial communities and environmental factors were important factors impacting the b/pARG profile. Among these factors, the bacterial community was the major driver that impacted the bARG profile, while bacterial community and MGEs were the major codrivers impacting the pARG profile. This study was the first to investigate the profiles of b/pARGs in pig farm WWTPs in China on such a large scale, providing a reference for the prevention and control of ARG pollution in agricultural environments.

The role of Ulva fasciata in the evolution of the microbial community and antibiotic resistance genes in maricultural sediments

This study explored changes in the microbial community and antibiotic resistance genes (ARGs) in maricultural clam sediment after 3-month co-culture with different densities (0, 5 and 12 g L^-1) of seaweed Ulva fasciata (U. fasciata). The maximum removal rates of NO₃^--N, PO₄^3--P, and inhibition of Vibrio culturability occurred at presence of 12 g L^-1U. fasciata. A significant decrease by 14.0% of the total ARGs was found in control sediment without U. fasciata after separation from the original niches, while the total ARGs further increased by 5.58%and 4.65% at presence of 5 and 12 g L^-1 of U. fasciata in compared with control sediment, respectively, strongly related with Chloroflexi, Spirochaetes, Proteobacteria and Bacteroidetes hosts. In addition, U. fasciata favored the decline of absolute gene numbers of some tetracycline resistance genes (tetPB, tetW, otrA, tetT, tetO) and class 1 integron-integrase gene.

Interrelationships between tetracyclines and nitrogen cycling processes mediated by microorganisms: A review

Due to their broad-spectrum antibacterial activity and low cost, tetracyclines (TCs) are a class of antibiotics widely used for human and veterinary medical purposes and as a growth-promoting agent for aquaculture. Interrelationships between TCs and nitrogen cycling have attracted scientific attention due to the complicated processes mediated by microorganisms. TCs negatively impact the nitrogen cycling; however, simultaneous degradation of TCs during nitrogen cycling mediated by microorganisms can be achieved. This review encapsulates the background and distribution of TCs in the environment. Additionally, the main nitrogen cycling process mediated by microorganisms were retrospectively examined. Furthermore, effects of TCs on the nitrogen cycling processes, namely nitrification, denitrification, and anammox, have been summarized. Finally, the pathway and microbial mechanism of degradation of TCs accompanied by nitrogen cycling processes were reviewed, along with the scope for prospective studies.

The relationship between culturable doxycycline-resistant bacterial communities and antibiotic resistance gene hosts in pig farm wastewater treatment plants

Pig farm wastewater treatment plants (WWTPs) are an important repository for resistant bacterial communities (RBCs) and antibiotic resistance genes (ARGs). However, the relationship between RBCs and ARG hosts has not been well characterized. In this study, water samples from influent and effluent from five pig farm WWTPs were collected. Gradient concentrations of doxycycline (DOX) were used to screen the culturable RBCs. The abundance of 21 subtypes of ARGs and the bacterial community were investigated. This study detected a large number of culturable DOX-RBCs and ARGs in the influent and effluent of pig farm WWTPs. The abundances of ARGs and RBCs in all effluent samples was significantly lower than that in the influent samples (P < 0.05), which indicated that the WWTPs can effectively remove most ARGs and RBCs in pig farm wastewater. The main potential culturable RBCs in pig farm wastewater were the dominant bacteria Proteobacteria, Actinobacteria, Pseudomonas, and Rheinheimera. However, most of the ARGs were mainly present in Bacteroidetes, Actinobacteria, Corynebacteriaceae, Macellibacteroides, Acinetobacter, and Enterobacteriaceae, which are considered potential ARG hosts. The results presented here showed that there were obvious differences between the species of culturable DOX-RBCs and ARG hosts in the pig farm WWTPs, which may be due to various environmental factors. This highlights the urgent need for further research on the relationship between RBCs and ARG hosts.

Variation in microbial populations and antibiotic resistance genes in mariculture sediments in the present of the seaweed Ulva fasciata and under selective pressure of oxytetracycline

The widely distributed seaweed Ulva fasciata has nutrient absorption abilities and can be used in the bioremediation of polluted maricultural environments. This study explored microbial community and antibiotic resistance gene (ARG) variation in mariculture sediments in response to different trace levels (10, 100, and 500 μg L^-1) of oxytetracycline (OTC) and the presence of Ulva fasciata. The increase in OTC level promoted nutrient (NO₃_-N and PO₄^3--P) removal mainly due to Ulva fasciata adsorption. The abundances of the Euryarchaeota and Planctomycetes phyla in sediments were positively related to the increase in OTC stress, while a negative correlation occurred for the Proteobacteria phylum via metagenomic analysis. Compared with the control system, the increase rates of total ARGs were 3.90%, 7.36% and 13.42% at the OTC levels of 10, 100 and 500 μg L^-1, respectively. OTC stress mainly favoured the collateral enrichment of non-corresponding polypeptide and MLS ARGs, mainly due to the enrichment of the phyla Planctomycetes and Euryarchaeota by the synergistic effect of OTC and nutrients. The results of quantitative PCR with tetracycline resistance genes (TRGs) (tetO, tetT, tetPB, tetW and otrA) and a horizontal transfer gene (intl1) demonstrated that all of genes had much higher gene numbers in sediments after 3 months of OTC stress than in those without OTC stress, which was strongly related to the variation in the phyla Bacteroidetes, Gemmatimonadetes and Acidobacteria. The significant correlation between intl1 and the target TRGs is indicative of the important role of the horizontal transfer of integron-resistant genes in the spread of TRGs.

Isolation of antibiotic-resistant bacteria in biogas digestate and their susceptibility to antibiotics

Antibiotics are widely used to prevent and treat diseases and promote animal growth in the livestock industry, and therefore antibiotic residues can end up in biogas digestate from processes treating animal manure (AM) and food waste (FW). These digestates represent a potential source of spread of antimicrobial resistance (AMR) when used as fertilisers. This study evaluated AMR risks associated with biogas digestates from two processes, using AM and FW as substrate, by isolation and identification of antibiotic-resistant bacteria (ARB) and testing their susceptibility to different antibiotics. ARB from the digestates were isolated by selective plating. The antibiotic susceptibility profile of isolates was determined using ampicillin, ceftazidime, meropenem, vancomycin, ciprofloxacin, rifampicin, chloramphenicol, clindamycin, erythromycin, tetracycline, gentamicin or sulfamethoxazole/trimethoprim, representing different antibiotic classes with differing mechanisms of action. In total, 30 different bacterial species belonging to seven genera were isolated and classified. Bacillus and closely related genera, including Paenibacillus, Lysinibacillus and Brevibacillus, were the dominant ARB in both digestates. Most of the ARB strains isolated were non-pathogenic and some were even known to be beneficial to plant growth. However, some were potentially pathogenic, such as an isolate identified as Bacillus cereus. Many of the isolated species showed multi resistance and the AM digestate and FW digestate both contain bacterial species resistant to all antibiotics tested here, except gentamicin. A higher level of resistance was displayed by the FW isolates, which may indicate higher antibiotic pressure in FW compared with AM digestate. Overall, the results indicate a risk of AMR spread when these digestates are used as fertiliser. However, most of the ARB identified are species commonly found in soil, where AMR in many cases is abundant already, so the contribution of digestate-based fertiliser to the spread of AMR may still be very limited.

Response of antibiotic resistance genes in constructed wetlands during treatment of livestock wastewater with different exogenous inducers: Antibiotic and antibiotic-resistant bacteria

This work aimed to study the behavior of antibiotic resistance genes (ARGs) in constructed wetlands with different exogenous inducers additions (oxytetracycline and its resistant bacteria) by high-throughput quantitative polymerase chain reaction. Results indicated that constructed wetlands have the potential to reduce ARGs relative abundances in wastewater, and the total ARGs removal efficiency could exceed 60%. ARGs profile in the effluent differed from that in the influent, and that did not directly reflect the export of dominant ARGs in wetland biofilms. Meanwhile, the highest levels of detected numbers and relative abundances of ARGs were 43 and 3.35 × 10^-1 for control system and 44 and 6.40 × 10^-1 for treatment system, respectively, which meant that ARGs generation in wetlands were inevitable, and antibiotic and antibiotic-resistant bacteria from wastewater could indeed promote ARGs abundance in the system. Compared to the single roles of inducers, their synergistic role had a more significant influence on ARGs relative abundance.

Dominant denitrifying bacteria are important hosts of antibiotic resistance genes in pig farm anoxic-oxic wastewater treatment processes

The anoxic-oxic (A/O) wastewater treatment process that is widely used in pig farms in China is an important repository for antibiotic resistance genes (ARGs). However, the distribution of ARGs and their hosts in the A/O process has not been well characterized. In this study, the wastewaters in the anoxic and oxic tanks for A/O processes were collected from 38 pig farms. The concentrations of 20 subtypes of ARGs, 5 denitrification-related genes, 2 integrons, and bacterial community composition were investigated. Bacterial genome binning was performed using metagenome sequencing. In this study, 20 subtypes of ARGs and integrons were detected in all sampling sites. A total of 16 of the 20 subtypes of ARGs were detected with the highest abundance in anoxic tanks, and sul1 was detected with a maximum average abundance of 19.21 ± 0.24 log₁₀ (copies/mL). Cooccurrence patterns were observed for some genes in the pig farm A/O process, such as sul1 and intl1, sul1 and tetG, and tetO and tetW. There was a significant cooccurrence pattern between the dominant denitrifying bacteria and some ARGs (bla_TEM, ermB, tetC, tetH and tetQ), so the dominant denitrifying bacteria were considered to be potential ARG hosts. In addition, 170 highly abundant bacterial genome bins were assembled and further confirmed that the denitrifying bacteria Brachymonas, Candidatus Competibacter, Thiobacillus and Steroidobacter were the important ARG hosts in the pig farm A/O process, providing a useful reference for the surveillance and risk management of ARGs in pig farm wastewater.

Performance of microbial fuel cell for treating swine wastewater containing sulfonamide antibiotics

The proper treatment of swine wastewater with relatively high concentrations of antibiotics is very important to protect environmental safety and human health. Microbial fuel cell (MFC) technology shows much promise for removing pollutants and producing electricity simultaneously. A double-chamber MFC was investigated in this study. Synthetic swine wastewater with the addition of sulfonamides was used as the fuels in the anode chamber. Results indicated that COD could be effectively removed (>95%) and virtually not affect by the presence of sulfonamides in the MFC. A stable voltage output was also observed. The removal efficiencies of sulfamethoxazole (SMX), sulfadiazine (SDZ), and sulfamethazine (SMZ) in the MFC were in the 99.46-99.53%, 13.39-66.91% and 32.84-67.21% ranges, respectively. These totals were higher than those reported for a traditional anaerobic reactor. Hence, MFC revealed strong resistance to antibiotic toxicity and high potential to treat swine wastewater with antibiotics.

How synthetic biology can help bioremediation

The World Health Organization reported that "an estimated 12.6 million people died as a result of living or working in an unhealthy environment in 2012, nearly 1 in 4 of total global deaths". Air, water and soil pollution were the significant risk factors, and there is an urgent need for effective remediation strategies. But tackling this problem is not easy; there are many different types of pollutants, often widely dispersed, difficult to locate and identify, and in many cases cost-effective clean-up techniques are lacking. Biology offers enormous potential as a tool to develop microbial and plant-based solutions to remediate and restore our environment. Advances in synthetic biology are unlocking this potential enabling the design of tailor-made organisms for bioremediation. In this article, we showcase examples of xenobiotic clean-up to illustrate current achievements and discuss the limitations to advancing this promising technology to make real-world improvements in the remediation of global pollution.