Spatiotemporal dynamic changes of antibiotic resistance genes in constructed wetlands and associated influencing factors

Biochar reduces plasmid-mediated antibiotic resistance gene transfer in earthworm ecological filters for rural sewage treatment

The spread of antibiotic resistance genes (ARGs) in rural wastewater threatens both ecological environment and human health. Earthworm ecological filters (EEFs) represent a green technology for rural sewage treatment. However, their effectiveness in removing ARGs remains a significant challenge. This study aims to investigate the role and underlying mechanisms of biochar addition in enhancing ARGs removal in rural sewage using EEFs. To achieve this, the fate of chromosome- and plasmid-carried ARGs was quantified in constructed EEFs, both with and without biochar addition. The results showed that the biochar could effectively remove ARGs from rural sewage, with a better removal efficiency for plasmid-carried ARGs. The absolute abundance of plasmid-carried ARGs in the effluent was reduced by 0.4-11 times compared to chromosomal ones, showing removal stability improved by 13.11-74.51 %. Additionally, the functional microbial community attached on the high porosity of biochar surface promoted ARGs retention, increasing diffusion limitation in microbial assembly mechanisms by 4.61-29.44 %, which played a key role in plasmid-mediated horizontal gene transfer (HGT). Partial least squares structural equation modeling (PLS-SEM) revealed that biochar-mediated environmental changes and the HGT of mobile genetic elements (MGEs) were critical factors in reducing plasmid-carried ARGs in EEFs.

High-throughput profiling of antibiotic resistance genes in the Yellow River of Henan Province, China

Profiling antibiotic resistance genes (ARGs) in the Yellow River of China's Henan Province is essential for understanding the health risks of antibiotic resistance. The profiling of ARGs was investigated using high-throughput qPCR from water samples in seven representative regions of the Yellow River. The absolute and relative abundances of ARGs and moble genetic elements (MGEs) were higher in summer than in winter (ANOVA, p < 0.001). The diversity and abundance of ARGs were higher in the Yellow River samples from PY and KF than the other sites. Temperature (r = 0.470 ~ 0.805, p < 0.05) and precipitation (r = 0.492 ~ 0.815, p < 0.05) positively influenced the ARGs, while pH had a negative effect (r = - 0.462 ~ - 0.849, p < 0.05). Network analysis indicated that the pathogenic bacteria Rahnella, Bacillus, and Shewanella were the possible hub hosts of ARGs, and tnpA1 was the potential MGE hub. These findings provide insights into the factors influencing ARG dynamics and the complex interaction among the MGEs, pathogenic bacteria and environmental parameters in enriching ARGs in the Yellow River of Henan Province.

Vermicompost: In situ retardant of antibiotic resistome accumulation in cropland soils

The dissemination of antibiotic resistance genes (ARGs) in soil has become a global environmental issue. Vermicomposting is gaining prominence in agricultural practices as a soil amendment to improve soil quality. However, its impact on soil ARGs remains unclear when it occurs in farmland. We comprehensively explored the evolution and fate of ARGs and their hosts in the field soil profiles under vermicompost application for more than 3 years. Vermicompost application increased several ARG loads in soil environment but decreased the high-risk bla-ARGs (blaampC, blaNDM, and blaGES-1) by log(0.04 - 0.43). ARGs in soil amended with vermicompost primarily occurred in topsoil (approximately 1.04-fold of unfertilized soil), but it is worth noting that their levels in the 40-60 cm soil layer were the same or even less than in the unfertilized soil. The microbial community structure changed in soil profiles after vermicompost application. Vermicompost application altered the microbial community structure in soil profiles, showing that the dominant bacteria (i.e., Proteobacteria, Actinobacteriota, Firmicutes) were decreased 2.62%-5.48% with the increase of soil depth. A network analysis further revealed that most of ARG dominant host bacteria did not migrate from surface soil to deep soil. In particular, those host bacteria harboring high-risk bla-ARGs were primarily concentrated in the surface soil. This study highlights a lower risk of the propagation of ARGs caused by vermicompost application and provides a novel approach to reduce and relieve the dissemination of ARGs derived from animals in agricultural production.

Typical antibiotic resistance genes and their association with driving factors in the coastal areas of Yangtze River Estuary

The massive use of antibiotics has led to the escalation of microbial resistance in aquatic environment, resulting in an increasing concern regarding antibiotic resistance genes (ARGs), posing a serious threat to ecological safety and human health. In this study, surface water samples were collected at eight sampling sites along the Yangtze River Estuary. The seasonal and spatial distribution patterns of 10 antibiotics and target genes in two major classes (sulfonamides and tetracyclines) were analyzed. The findings indicated a high prevalence of sulfonamide and tetracycline resistance genes along the Yangtze River Estuary. Kruskal-Wallis analysis revealed significant seasonal variations in the abundance of all target genes. The accumulation of antibiotic resistance genes in the coastal area of the Yangtze River Estuary can be attributed to the influence of urban instream runoff and the discharge of effluents from wastewater treatment plants. ANISOM analysis indicated significant seasonal differences in the microbial community structure. VPA showed that environmental factors contribute the most to ARG variation. PLS-PM demonstrate that environmental factors and microbial communities pose direct effect to ARG variation. Analysis of driving factors influencing ARGs in this study may shed new insights into the mechanism of the maintenance and propagation of ARGs.

Vertical distribution characteristics and transport paths of antibiotic resistance genes in constructed wetland system

Although the migration and diffusion of antibiotic resistance genes (ARGs) in soil-plant systems have attracted much attention, the migration and diffusion characteristics between constructed wetlands and soil-plant systems differ greatly. Therefore, it is necessary to conduct research on vertical transmission and diffusion of ARGs in constructed wetlands. The vertical distribution and transmission of ARGs in constructed wetlands were explored via metagenomic analysis. The results showed that the proportion of multidrug ARGs was the largest, ranging from 24.2% to 47.5%. The shared characteristics of ARGs were similar to those of bacteria, and there were fewer unique ARGs and microbial species in mesophyll tissue. Sourcetracker analysis revealed that ARGs transfer between plants and atmosphere was bidirectional, but the diffusion of ARGs to atmosphere through plants was relatively weak. ARGs were mainly transmitted to atmosphere/surrounding environment through substrate and influent, and the contributions of substrate to ARGs in atmosphere/surrounding environment were 59.2% and 78.6%, respectively. ARGs involved in foliar attachment mainly originated from peripheral inputs. ARGs showed nonspecific selection for the host at phylum, class and order levels. These findings suggest that more attention should be given to the potential risks of ARGs in constructed wetlands, to formulate effective control and management strategies.

The critical role of microplastics in the fate and transformation of sulfamethoxazole and antibiotic resistance genes within vertical subsurface-flow constructed wetlands

Constructed wetlands (CWs) are reservoirs of microplastics (MPs) in the environment. However, knowledge about the impact of MPs on antibiotic removal and the fate of antibiotic resistance genes (ARGs) is limited. We focused on sulfamethoxazole (SMX) as a representative compound to examine the effects of MPs on SMX removal and the proliferation and dissemination of two SMX-related ARGs (sul1 and sul2) in vertical subsurface-flow CW (VFCW) microcosm. The presence of MPs in the substrate was found to enhance the proliferation of microorganisms owing to the large specific surface area of the MPs and the release of dissolved organic carbon (DOC) on MP surfaces, which resulted in a high SMX removal ranging from 97.80 % to 99.80 %. However, the presence of MPs promoted microbial interactions and the horizontal gene transfer (HGT) of ARGs, which led to a significant increase in the abundances of sul1 and sul2 of 68.47 % and 17.20 %, respectively. It is thus imperative to implement rigorous monitoring strategies for MPs to mitigate their potential ecological hazards.

Determining the spatiotemporal variation, sources, and ecological processes of antibiotic resistance genes in a typical lake of the middle reaches of the Yangtze River

Antibiotic resistance genes (ARGs) are emerging environmental pollutants, influenced by complex regulatory factors. River-lake systems act as natural reservoirs for ARGs and provide an ideal model for studying their regulatory mechanisms. This study employed high-throughput quantitative PCR, high-throughput sequencing, correlation analyses, and model predictions to investigate the dynamics of ARGs and their influencing factors in Liangzi Lake, located in the mid-reaches of the Yangtze River. The research specifically centered on three environmental components: lake water, sediment, and river water. Results indicated that the ARGs from eight major antibiotic classes, displaying distinct seasonal distribution patterns. In comparison to the sediment, the water phase demonstrated a higher diversity of ARGs, with the highest level of ARGs sharing observed between lake and river waters (approximately 83.7 %). Furthermore, seasonal variations significantly influenced the distributions of both ARGs and bacterial communities. The diversity of ARGs was highest during the summer and autumn, and specific bacterial species exhibited robust correlations with ARGs (including matA/mel, aac (6')-Ib-03, and blaROB). It is worth noting that environmental attributes and bacterial diversity had the most substantial impact on the dynamic changes in ARGs. Lastly, source tracking analysis pinpointed that sediment as the primary source of ARGs in lake water, constituting 45 % to 48 % of the total ARGs. Our study provides a comprehensive analysis of ARGs and their influencing factors in the river-lake system of the middle reaches of the Yangtze River, with Liangzi Lake as a representative case.

Purification of aquaculture wastewater by macrophytes and biofilm systems: Efficient removal of trace antibiotics and enrichment of antibiotic resistance genes

The purification performance of aquaculture wastewater and the risk of antibiotic resistance genes (ARGs) dissemination in wetlands dominated by macrophytes remain unclear. Here, the purification effects of different macrophytes and biofilm systems on real aquaculture wastewater were investigated, as well as the distribution and abundance of ARGs. Compared to the submerged macrophytes, artificial macrophytes exhibited higher removal rates of TOC (58.80 ± 5.04 %), TN (74.50 ± 2.50 %), and TP (77.33 ± 11.66 %), and achieved approximately 79.92 % removal of accumulated trace antibiotics in the surrounding water. Additionally, the biofilm microbial communities on the surface of artificial macrophytes exhibited higher microbial diversity with fewer antibiotic-resistant bacteria (ARB) enrichment from the surrounding water. The absolute abundance of ARGs (sul1, sul2, and intI1) in the mature biofilm to be one to two orders of magnitude higher than that in the water. Although biofilms could decrease ARGs in the surrounding water by enriching ARB, the intricate network structure of biofilms further facilitated the proliferation of ARB and the dissemination of ARGs in water. Network analysis suggested that Proteobacteria and Firmicutes phyla were dominant and potential carriers of ARGs, contributing 69.00 % and 16.70 %, respectively. Our findings highlight that macrophytes and biofilm systems have great performance on aquaculture wastewater purification, but with high risk of ARGs.

Antibiotic resistance genes in constructed wetlands: Driving indicators and risk assessment

Constructed wetlands (CWs) were responsible for the in-depth purification of wastewater, providing an ideal environment for the transport, acquisition, and dissemination of antibiotic resistance genes (ARGs). A better understanding of influencing factors and risks of ARGs in CWs was deemed indispensable. In this research, the abundance of ARGs and mobile genetic elements (MGEs) was determined to be higher in summer and spring, ranging from 53.7 to 8.51 × 106 and 30.9-6.02 × 106 copies/mL, respectively. Seasonal variation significantly influenced the abundance of ARGs and MGEs, as well as the co-occurrence patterns among ARGs, MGEs and bacteria. However, the environmental gradients, from the influent (CW01) to the effluent (CW10), did not impose significant effects on the abundance of ARGs and MGEs. Furthermore, the ratios of pathogenic bacteria to ARG hosts and ARG risks index decreased by 50.4% and 88.54% along with the environmental gradients, indicating that CWs could act as barriers to the transfer of ARGs. Partial least squares-path modeling (PLSPM) revealed that temperature was the main driving factor of ARGs, followed by MGEs, stable and differential bacteria. This finding effectively and innovatively explored the driving indicators for the variations and risks of ARGs caused by spatial-temporal variations, providing new insights into the evaluation and control of ARGs in CWs.

Implications of vermicompost on antibiotic resistance in tropical agricultural soils - A study in Hainan Island, China

The contamination of antibiotic resistance genes (ARGs) associated with animal manure fertilization have attracted a global concern. Vermicompost has been widely popularized as an eco-friendly alternative to recycle animal manure on Hainan Island, China. However, the effects of vermicompost application on ARG spread and environmental fate in tropical agricultural soils remains undefined. Herein, the spatial prevalence and vertical behavior of ARGs in the soil profiles of vermicompost-applied agricultural regions were explored by a large-scale survey across Hainan Island. The results showed that although vermicompost application marginally enhanced the load of ARG pollution in the soil in Hainan, the ARGs derived from vermicompost did not eventually accumulate in the soil profile. The increase rate of ARGs in 40-60 cm soil layer was only 0.0015 % compared with that of unfertilized soil. Interestingly, vermicompost application reduced the abundance of high-risk ARGs, such as blaNDM and blaampC, by approximately one order of magnitude. Vermicompost was also observed to increase the abundance of beneficial bacteria, like Clostridium, and decrease those of Acidobacteriae, Planctomycetes and Verrucomicrobiae, which caused changes in the potential host bacteria of soil ARGs. Mobile genetic elements were further proven to be an essential factor that regulated the vertical dynamics of ARGs in vermicomposted soil, with a direct influence coefficient of 0.9975. This study demonstrated that the controllable risk associated with vermicompost application provided useful information to effectively reduce the threat of ARGs and promote the development of sustainable agriculture on Hainan Island.

Occurrence of antibiotics in wastewater: Potential ecological risk and removal through anaerobic-aerobic systems

Antibiotics are intensively used to improve public health, prevent diseases and enhance productivity in animal farms. Contrarily, when released, the antibiotics laden wastewater produced from pharmaceutical industries and their application sources poses a potential ecological risk to the environment. This study provides a discussion on the occurrence of various antibiotics in wastewater and their potential ecological risk in the environment. Further, a critical review of anaerobic-aerobic processes based on three major systems (such as constructed wetland, high-rate bioreactor, and integrated treatment technologies) applied for antibiotics removal from wastewater is performed. The review also explores microbial dynamics responsible for antibiotic biodegradation in anaerobic-aerobic systems and its economic feasibility at wider-scale applications. The operational problems and prospective modifications are discussed to define key future research directions. The appropriate selection of treatment processes, sources control, understanding of antibiotic fate, and adopting precise monitoring strategies could eliminate the potential ecological risks of antibiotics. Integrated bio-electrochemical systems exhibit antibiotics removal ≥95% by dominant Geobacter sp. at short HRT ∼4-10 h. Major process factors like organic loading rate, hydraulic loading rate (HRT), and solid retention time significantly affect the system performance. This review will be beneficial to the researchers by providing in-depth understanding of antibiotic pollution and its abatement via anaerobic-aerobic processes to develop sustainable wastewater treatment technology in the future.

Accumulation and ecotoxicological effects induced by combined exposure of different sized polyethylene microplastics and oxytetracycline in zebrafish

Microplastics have been widely reported as carriers of antibiotics, yet studies investigating the combined ecotoxicology of microplastics and antibiotics on organisms is limited. In this study, different sized polystyrene plastics and oxytetracycline (OTC) were used to carry out a 30-day single and binary-combined exposure experiment of zebrafish, and the microplastics and OTC accumulation, liver histological alteration, biomarkers and transcriptomic response of zebrafish were evaluated. Our results indicated that 300 nm and 50 nm plastic particles increased the OTC accumulation in liver by 33.8% and 44.5%, respectively. Microplastics and OTC induced severe liver histological damage, and the damage is size-dependent, increasing with the decrease of microplastics sizes. The liver biomarkers indicated a different response pattern in single microplastics exposure and combined with OTC, single or co-exposure of 50 nm nano-plastics and OTC induced intense responses of integrated biomarker response values. The 50 nm nano-plastics, OTC and their combined exposure induced 1330, 2693 and 3965 significantly differentially expressed genes, respectively, in which the steroid biosynthesis pathway was significantly affected by all the three treatments. This study elucidated the size-dependent effects of microplastics and provided detailed data from histopathology to transcriptome profile, enhancing our understanding of the ecotoxicity of microplastics and OTC.

Influencing factors of antibiotic resistance genes removal in constructed wetlands: A meta-analysis assisted by multivariate statistical methods

In order to control antibiotic resistance genes (ARGs) diffusion in constructed wetlands, it is critical to explore the main factors influencing ARGs removal and understand its mechanism. Despite the fact that numerous studies have been conducted to determine the factors influencing ARGs removal by constructed wetlands in recent years, attempts to use published data and incorporate them into a comprehensive comparison and analysis are still limited. A framework for literature collection, data extraction and statistical analysis (LDS) was constructed in this study. The main factors influencing antibiotics and ARGs removal by constructed wetlands were identified using this framework. The results showed that nutrients, types of constructed wetlands and hydraulic loading were the principal factors influencing the removal of most antibiotics. The principal factors influencing the most ARGs removal were mobile genetic elements, plants, volume of constructed wetlands and running time. After purification by constructed wetlands, the risk coefficient of antibiotics decreased significantly, while the relative abundance of most ARGs did not change significantly. The analysis results of linear mixed model showed that the relationship between antibiotics and ARGs in effluent was closer than that in influent. LDS framework provides a new platform for the study of influencing factors of pollutant removal based on data mining.

Characteristics of resistome and bacterial community structure in constructed wetland during dormant period: A fullscale study from Annan wetland

As a green technology, constructed wetlands (CWs) can provide a low-cost solution for wastewater treatment. Either as a standalone treatment or integrated with conventional treatment, nutrients, antibiotic resistant bacteria (ARB)/antibiotic resistance genes (ARGs) can be removed by CW efficiently. While, few studies have focused on characteristics of resistome and bacterial community (BC) structure in CW during dormant period. Therefore, in this study, Annan CW (a full-scale hybrid CW) was selected to characterize resistome and BC during dormant period. The profiles of bacteria / ARGs were monitored in combination of shotgun sequencing and metagenomic assembly analysis. And multidrug ARGs are the most abundant in Annan CW, and surface flow wetland had the relatively high ARG diversity and abundance compared with subsurface flow wetland and the front pond. The most dominant phylum in CW is Proteobacteria, while the other dominant phylum in three parts have different order. COD, TP, TN, ARGs, and mobile genetic genes (MGEs) were removed by subsurface flow CW with better performance, but virulent factors (VFs) were removed by surface flow CW with better performance. Based on the spatiotemporal distribution of ARGs, the internal mechanism of ARGs dynamic variation was explored by the redundancy analysis (RDA) and variation partitioning analysis (VPA). BCs, MGEs and environmental factors (EFs) were responsible for 45.6 %, 28.3 % and 15.4 % of the ARGs variations. Among these factors, BCs and MGEs were the major co-drivers impacting the ARG profile, and EFs indirectly influence the ARG profile. This study illustrates the specific functions of ARG risk elimination in different CW components, promotes a better understanding of the efficiency of CWs for the reduction of ARG and ARB, contributing to improve the removal performance of constructed wetlands. And provide management advice to further optimize the operation of CWs during dormant period.