Deciphering the antibiotic resistome and microbial community in municipal wastewater treatment plants at different elevations in eastern and western China

Strong suppression of silver nanoparticles on antibiotic resistome in anammox process

This study comprehensively deciphered the effect of silver nanoparticles (AgNPs) on anammox flocculent sludge, including nitrogen removal performance, microbial community structure, functional enzyme abundance, antibiotic resistance gene (ARGs) dissemination, and horizontal gene transfer (HGT) mechanisms. After long-term exposure to 0-2.5 mg/L AgNPs for 200 cycles, anammox performance significantly decreased (P < 0.05), while the relative abundances of dominant Ca. Kuenenia and anammox-related enzymes (hzsA, nirK) increased compared to the control (P < 0.05). For antibiotic resistome, ARG abundance hardly changed with 0-0.5 mg/L AgNPs but decreased by approximately 90% with 1.5-2.5 mg/L AgNPs. More importantly, AgNPs effectively inhibited MGE-mediated HGT of ARGs. Additionally, structural equation model (SEM) disclosed the underlying relationship between AgNPs, the antibiotic resistome, and the microbial community. Overall, AgNPs suppressed the anammox-driven nitrogen cycle, regulated the microbial community, and prevented the spread of ARGs in anammox flocs. This study provides a theoretical baseline for an advanced understanding of the ecological roles of nanoparticles and resistance elements in engineered ecosystems.

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.

Dissolved organic nitrogen is a key to improving the biological treatment potential of landfill leachate

Biological treatment is one of the most promising efficient, low-carbon and affordable approaches for the treatment of recalcitrantly degradable wastewater, such as landfill leachate. However, even the macroscopic molecular level analysis of dissolved organic matter (DOM) is limiting to the enhancement of biological treatment efficacy, and there is an urgent need for deeper exploration of DOM to gain insights into the key constraining substances. In the present study targeting at piercing leachate organic at molecular level, nitrogen-containing dissolved organic matter (DOMN) was identified to be the bottleneck that govern the biotreatment potential. The conclusion was made based on two series of experiments that compared the same anoxic-aerobic membrane bioreactor process (A process) operated stably at different regions, and compared with C process that coupling A process with a circulation aeration membrane bioreactor to improve aeration efficiency. The results confirmed that the relative abundance of DOMN was absolutely dominant among the three categories of DOM in all biologically treated samples, contributing to 60.36 %-65.81 % in removed-DOM, 60.33 %-70.95 % in refractory-DOM and 63.14 %-71.36 % in derived-DOM. Specifically, the high latitude A process had much lower DOMN removal rate than the low latitude A process (p < 0.05) and much higher refractory and derivatization rates than the low latitude A process (p < 0.05). DOM had similar results. No statistically significant differences were observed in the proportion of the three categories of DOM (DOMN), the elements composition, and the subcategory composition of the C process compared to the A process, in which the DOM (DOMN) derivation rate of NEC1-C (31.92 % and 33.41 %) was much higher than that of NEC1-A (20.88 % and 22.19 %). However, the AIwa and AImodwa of the derived-DOM (DOMN) were significantly higher in the C process than in the A process, which implied that excessive aeration did not enhance the biological treatment potential of the A process, but instead led to the proliferation of microorganisms and the secretion of extracellular polymer substances, which resulted in the derivation of more complex compounds. The results of the correlation analysis indicated that there were some regional differences in the molecular information of DOMN driven by climate temperature. In addition, it was worth mentioning that the nominal oxidation state of carbon (NOSCwa) of derived-DOMN in different regions of A process was noticeably higher than the corresponding DOM (p < 0.0001), implying that the derived-DOMN were still highly biodegradable, in other words, there was still great room for improving the biological treatment potential of landfill leachate. The present study provided a deeper insight and analysis of landfill leachate at the molecular level (DOMN) through multiple practical engineering cases, with a view to providing a theoretical basis for efficient optimization of biological treatment.

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

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

Impact of uranium on antibiotic resistance in activated sludge

The emergence of antibiotic resistance genes (ARGs) and antibiotic-resistant bacteria (ARB) in the environment is well established as a human health crisis. The impact of radioactive heavy metals on ecosystems and ultimately on human health has become a global issue, especially for the regions suffering various nuclear activities or accidents. However, whether the radionuclides can affect the fate of antibiotic resistance in bacteria remains poorly understood. Here, the dynamics of ARB, three forms of ARGs-intracellular ARGs (iARGs), adsorbed extracellular ARGs (aeARGs), and free extracellular ARGs (feARGs)-and microbial communities were investigated following exposure to uranium (U), a representative radioactive heavy metal. The results showed that 90-d of U exposure at environmentally relevant concentrations of 0.05 mg/L or 5 mg/L significantly increased the ARB concentration in activated sludge (p < 0.05). Furthermore, 90-d of U exposure slightly elevated the absolute abundance of aeARGs (except tetO) and sulfonamide iARGs, but decreased tetracycline iARGs. Regarding feARGs, the abundance of tetC, tetO, and sul1 decreased after 90-d of U stress, whereas sul2 showed the opposite trend. Partial least-squares path model analysis revealed that the abundance of aeARGs and iARGs under U stress was predominantly driven by increased cell membrane permeability/intI1 abundance and cell membrane permeability/reactive oxygen species concentration, respectively. Conversely, the changes in feARGs abundance depended on the composition of the microbial community and the expression of efflux pumps. Our findings shed light on the variations of ARGs and ARB in activated sludge under U exposure, providing a more comprehensive understanding of antibiotic resistance risks aggravated by radioactive heavy metal-containing wastewater.

Antibiotic resistance genes associated with size-segregated bioaerosols from wastewater treatment plants: A review

The antibiotic-resistant pollution in size-segregated bioaerosols from wastewater treatment plants (WWTPs) is of increasing concern due to its public health risks, but an elaborate review is still lacking. This work overviewed the profile, mobility, pathogenic hosts, source, and risks of antibiotic resistance genes (ARGs) in size-segregated bioaerosols from WWTPs. The dominant ARG type in size-segregated bioaerosols from WWTPs was multidrug resistance genes. Treatment units that equipped with mechanical facilities and aeration devices, such as grilles, grit chambers, biochemical reaction tanks, and sludge treatment units, were the primary sources of bioaerosol antibiotic resistome in WWTPs. Higher enrichment of antibiotic resistome in particulate matter with an aerodynamic diameter of <2.5 μm, was found along the upwind-downwind-WWTPs gradient. Only a small portion of ARGs in inhalable bioaerosols from WWTPs were flanked by mobile genetic elements. The pathogens with multiple drug resistance had been found in size-segregated bioaerosols from WWTPs. Different ARGs or antibiotic resistant bacteria have different aerosolization potential associated with bioaerosols from various treatment processes. The validation of pathogenic antibiotic resistance bacteria, deeper investigation of ARG mobility, emission mechanism of antibiotic resistome, and development of treatment technologies, should be systematically considered in future.

Metagenomic insights into the nitrogen metabolism, antioxidant pathway, and antibiotic resistance genes of activated sludge from a sequencing batch reactor under tetracycline stress

Tetracycline is prevalent in wastewater treatment plants and poses a potential threat to biological nitrogen removal under long-term exposure. In the present study, the influence of different tetracycline concentrations on the nitrogen removal, bioactivity response, and the spread of antibiotic resistance genes (ARGs) was assessed in sequencing batch reactor (SBR). The nitrogen removal efficiency, nitrification rate, and denitrification rate and their corresponding enzymatic activities gradually decreased with an increase in tetracycline concentration from 0.5 to 15 mg/L. The remarkable toxicity induced by tetracycline led to a significant increase in the peroxidation and the response of antioxidant system, as evidenced by strengthened antioxidant enzymatic activity and abundant genes (SOD12, katG, PXDN, gpx, and apx). Tetracycline addition significantly inhibited the ammonia-oxidizing bacterium Nitrosomonas and functional genes (amoA, amoB, and amoC). The presence of tetracycline decreased the abundance of citrate synthase and genes (CS, IDH3, and acnA) and interfered with carbon source metabolism, leading to impaired bioactivity and treatment performance. In addition, the presence of tetracycline induces diversity and differences in ARGs. The results provide reliable basic data for a deeper understanding of the effects of tetracycline on the nitrogen removal performance of bioreactors and provide a theoretical basis to build a promising strategy for relieving antibiotic-caused process fluctuations.

Metagenomic insight into the prevalence and driving forces of antibiotic resistance genes in the whole process of three full-scale wastewater treatment plants

The spread of antibiotic resistance genes (ARGs) is an emerging global health concern, and wastewater treatment plants (WWTPs), as an essential carrier for the occurrence and transmission of ARGs, deserves more attention. Based on the Illumina NovaSeq high-throughput sequencing platform, this study conducted a metagenomic analysis of 18 samples from three full-scale WWTPs to explore the fate of ARGs in the whole process (influent, biochemical treatment, advanced treatment, and effluent) of wastewater treatment. Total 70 ARG subtypes were detected, among which multidrug, aminoglycoside, tetracycline, and macrolide ARGs were most abundant. The different treatment processes used for three WWTPs were capable of reducing ARG diversity, but did not significantly reduce ARG abundance. Compared to that by denitrification filters, the membrane bioreactor (MBR) process was advantageous in controlling the prevalence of multidrug ARGs in WWTPs. Linear discriminant analysis Effect Size (LEfSe) suggested g_Nitrospira, g_Curvibacter, and g_Mycobacterium as the key bacteria responsible for differential ARG prevalence among different WWTPs. Meanwhile, adeF, sul1, and mtrA were the persistent antibiotic resistance genes (PARGs) and played dominant roles in the prevalence of ARGs. Proteobacteria and Actinobacteria were the host bacteria of majority ARGs in WWTPs, while Pseudomonas and Nitrospira were the most crucial host bacteria influencing the dissemination of critical ARGs (e.g., adeF). In addition, microbial richness was determined to be the decisive factor affecting the diversity and abundance of ARGs in wastewater treatment processes. Overall, regulating the abundance of microorganisms and key host bacteria by selecting processes with microbial interception, such as MBR process, may be beneficial to control the prevalence of ARGs in WWTPs.

Land-derived wastewater facilitates antibiotic resistance contamination in marine sediment of semi-closed bay: A case study in Jiaozhou Bay, China

The emergence of antibiotic resistance is a severe threat to public health. There are few studies on the effects of sewage discharge on antibiotics and antibiotic resistance genes (ARGs) contamination in Jiaozhou Bay sediment. Herein, a total of 281 ARG subtypes, 10 mobile genetic elements (MGEs), 10 antibiotics and bacterial communities in marine sediments from Jiaozhou Bay were characterized. Similar bacterial community structures and ARG profiles were identified between the various sampling sites inside the bay, which were both dominated by multidrug and (fluoro)quinolone resistance genes and harbored lower relative abundances of ARGs than those in the sampling sites near the bay exit. Compared with antibiotics and MGEs, bacterial community composition was a more important driver of ARG diversity and geographic distribution. The abundance of pathogens carrying genetic information increased dramatically in southern Jiaozhou Bay is affected by sewage discharge, which indicating that wastewater discharge facilitated ARG contamination of marine sediments. This study highlights the risk of disseminating antibiotic resistance-influencing factors from treated wastewater discharge into marine environment there is an urgent need to optimize or improve wastewater treatment processes to enhance the removal of antibiotics and ARGs. This study has necessary implications for filling the gap in information on antibiotic resistance in Jiaozhou Bay and developing future pollution regulation and control measures.

Ecological Risks of Antibiotics in Urban Wetlands on the Qinghai-Tibet Plateau, China

Although the ecological risks of antibiotics have been extensively researched globally, fewer studies have been conducted in sensitive and fragile plateau wetland ecosystems. To evaluate the ecological risk of antibiotics in plateau urban wetlands, 18 water samples, 10 plant samples, and 8 sediment samples were collected in March 2022 in the Xining urban wetlands on the Qinghai-Tibet Plateau. The liquid chromatography-electrospray ionization tandem mass spectrometry method was utilized to measure the concentrations of 15 antibiotics in three categories in three types of environmental media. Risk quotients were adopted to assess the ecological risk of antibiotics, and the principal component analysis-multiple linear regression model was used to analyze the source of antibiotics. The results showed that (1) the maximum concentrations of antibiotics in water samples, plants, and sediments reached 1220.86 ng/L, 78.30 ng/g, and 5.64 ng/g, respectively; (2) Tylosin (TYL), norfloxacin (NFX), ofloxacin (OFX), and ciprofloxacin (CFX) in water were at medium and high-risk levels, and OFX had the highest risk value, of 108.04; and (3) the results of source apportionment indicate that 58.94% of the antibiotics came from the Huangshui river and wastewater treatment plant (WWTP) near the wetlands. The current study may provide a reference for the risks and management of antibiotics in plateau urban wetlands.