Metagenomic insights into the spatiotemporal responses of antibiotic resistance genes and microbial communities in aquaculture sediments

The impact of microplastics on antibiotic resistance genes, metal resistance genes, and bacterial community in aquaculture environment

Microplastics are emerging contaminants. However, their effects on antibiotic resistance genes (ARGs), metal resistance genes (MRGs), and the structure and abundance of bacterial communities, particularly pathogens, in aquaculture environments remains poorly understood. Therefore, this study investigated the effect of microplastics of different sizes on the abundance and distribution of ARGs, MRGs, and bacterial communities in aquaculture environments. The results revealed that, compared with pond water, large microplastics harbored significantly higher ARG abundances, particularly for multidrug-resistant genes; notably, level-I- and -II-risk ARGs were more prevalent on microplastics, highlighting the potential for horizontal gene transfer. Microplastics also exhibited a propensity to aggregate pathogenic bacteria such as Brucella and Pseudomonas, which could pose direct risks to aquatic product safety and public health. Network and differential network analyses revealed significant correlations between bacterial genera and ARG/MRG abundance, particularly on microplastics. Therefore, our findings suggest that microplastics act as vectors for the spread of ARGs, MRGs, and pathogens in aquaculture, potentially leading to the formation of complexes of these materials that threaten ecosystem health and human well-being. This study provides critical insights into the need for targeted management strategies to mitigate microplastic pollution in aquaculture settings.

Characterization and risk-quantification of antibiotic resistome in grain-based and non-grain cropping soils

Microbial contamination in soils, encompassing human bacterial pathogens (HBPs), antibiotic resistance genes (ARGs), and virulence factor genes (VFGs), poses a significant threat to human health via the food chain. Currently, there is a lack of comprehensive assessments of microbial contamination and associated health risks of ARGs in agricultural soils. In this study, metagenomic sequencing was used to evaluate microbial contamination in grain-based cropping soils (rice cultivation) and non-grain cropping soils (vegetable cultivation and aquaculture). The results showed that the diversity and abundance of HBPs and VFGs were significantly higher in non-grain soils. Further resistome analysis revealed higher abundances of high-risk (from 0.014 to 0.018-0.023) and "last-resort" ARGs (from 0.007 to 0.034-0.046) in non-grain soils. Besides ARGs abundance, health risk quantification revealed that non-grain soils exhibited 1.49-2.14-fold greater ARG-related risks than grain-based soils. Additionally, stronger network associations were found between HBPs, ARGs, and mobile genetic elements (MGEs) in non-grain soils. This study indicated that the non-grain cropping pattern of soils elevated the risk of microbial contamination and ARGs health risk, which provided an important basis for accurately quantifying the risk of microbial contamination in different agricultural soils.

Dechloromonas aquae sp. nov., A Novel Species Isolated from Aquaculture Water of Grass Carp

A novel bacterial strain, designated Dechloromonas aquae ZY10T, was isolated from the aquaculture water of grass carp. The colonies exhibited diameters ranging from approximately 1 to 3 mm and were characterized by a creamy-white coloration, circular shape, smooth texture, translucency, and a convex profile. The cells were facultatively anaerobic and motile, utilizing a single polar flagellum for movement. They were rod-shaped, reproduced through binary fission, and were identified as Gram-negative, oxidase-negative, and catalase-positive. Optimal growth was observed between 37 and 40 °C, within a pH range of 7.0-9.0, and at a NaCl concentration of 0% (w/v). The respiratory quinone was ubiquinone-8 (97.6%) and ubiquinone-7 (2.4%), and the major polar lipids were phosphatidylethanolamine (PE), aminophospholipid (APL), diphosphatidylglycerol (DPG), and phosphatidylglycerol (PG). Phylogenetic analysis based on 16S rRNA gene sequences suggested that ZY10T formed a lineage within the genus Dechloromonas and showed the highest 16S rRNA gene sequence similarity to "D. hankyongensis" XY25T (96.5%), followed by D. denitrificans ED1T (96.4%), D. hortensis MA-1T (96.1%) and D. agitata CKBT (96.0%) and Azonexus. caeni Slo-05T (95.5%). The predominant fatty acids of ZY10T were summed feature 3 (comprising C16:1 ω6c and/or C16:1 ω7c) and C16:0. The whole genome of ZY10T was 3,568,927 bp in size, including 3,275 protein-coding genes, 72 tRNA genes, and 15 rRNA genes, and the genomic DNA G + C content was 62.0 mol%. The orthologous average nucleotide identity, average amino acid identity, and digital DNA-DNA hybridization values between ZY10T and other species within the family Azonexaceae were 78.0-81.5%, 71.8-73.9%, and 20.3-23.0%, respectively. Therefore, based on phenotypic, chemotaxonomic, and phylogenetic analyses, the isolated ZY10T (= MCCC 1K08699T = KCTC 72749 T) is proposed as type strain of the novel species Dechloromonas aquae sp. nov.

In Vitro Antimicrobial Activity of Volatile Compounds from the Lichen Pseudevernia furfuracea (L.) Zopf. Against Multidrug-Resistant Bacteria and Fish Pathogens

Lichens are symbiotic organisms with unique secondary metabolism. Various metabolites from lichens have shown antimicrobial activity. Nevertheless, very few studies have investigated the antimicrobial potential of the volatile compounds they produce. This study investigates the chemical composition and antimicrobial properties of volatile compounds from Pseudevernia furfuracea collected in two regions of Morocco. Hydrodistillation was used to obtain volatile compounds from samples collected in the High Atlas and Middle Atlas. Gas chromatography-mass spectrometry (GC-MS) analysis identified phenolic cyclic compounds as the primary constituents, with atraric acid and chloroatranol being the most abundant. Additionally, eight compounds were detected in lichens for the first time. The antimicrobial activity of these compounds was assessed using disc diffusion and broth microdilution methods. Both samples demonstrated significant antimicrobial effects against multidrug-resistant human bacteria, reference microorganisms, fish pathogens, and Candida albicans, with minimum inhibitory concentrations (MICs) ranging from 1000 µg/mL to 31.25 µg/mL. This study provides the first report on the volatile compounds from Pseudevernia furfuracea and their antimicrobial effects, particularly against fish pathogens, suggesting their potential as novel antimicrobial agents for human and veterinary use. Further research is warranted to explore these findings in more detail.

Metagenomic analysis unveiled the response of microbial community and antimicrobial resistome in natural water body to duck farm sewage

Sewages from duck farms are often recognized as a major source of antimicrobial resistance and pathogenic bacteria discharged to natural water bodies, but few studies depicted the dynamic changes in resistome and microbial communities in the rivers under immense exposure of sewage discharge. In this study, we investigated the ecological and environmental risks of duck sewages to the rivers that geographically near to the duck farms with short-distance (<1 km) using 16S rRNA amplicon and metagenomic sequencing. The results showed that a total of 20 ARG types were identified with abundances ranged from 0.61 to 1.33 cpc. Of note, the genes modulate resistances against aminoglycoside, bacitracin and beta-lactam were the most abundant ARGs. Limnohabitans, Fluviibacter and Cyanobium were the top 3 predominant genera in the microbial community. The alpha diversity of overall microbial community decrease while the abundance of pathogen increase during the input of sewage within 200 m. Sul1 and bacA were the dominant ARGs brought from duck farm sewage. The community variations of ARGs and microbiome were primarily driven by pH and temperature. Total phosphorus was significantly correlated to alpha diversity and top 30 ARGs subtype. Stochastic processes was the dominated microbial assembly pattern and did not be altered by sewage. We also highlighted the ecological risk caused by blaGES which possibly could be mitigated by Cyanobacteria, and the natural water body can purify partial ARGs as well as microbiome from duck farms sewage. These findings expanded our knowledge regarding the ecological risks by wastes from the livestock farm, and underscoring the necessity to monitor ARGs in farm-surrounding water bodies.

Bacterial mercury methylation modulated by vitamin B9: An overlooked pathway leads to increased environmental risks

There has been a serious health and environmental concern in conversion of inorganic mercury (Hg) to the neurotoxin, methylmercury (MeHg) by anaerobic microbes, while very little is known about the potential role of vitamin B9 (VB9) regulator in the biochemical generation of MeHg. This study innovatively investigated bacterial Hg methylation by Geobacter sulfurreducens PCA in the presence of VB9 under two existing scenarios. In the low-complexing scenario, the bacterial MeHg yield reached 68 % higher than that without VB9 within 72 h, which was attributed to free VB9-protected PCA cells relieving oxidative stress, as manifested by the increased expression of Hg methylation gene (hgcAB cluster by 19-48 %). The high-complexing scenario emphasized the intracellular Hg accumulation (38-45 %) after 12 h, as indicated by the increased expression of outer membrane protein-related and mercuric reductase-encoding genes, indicating the inefficient bioavailability of Hg due to a gradual shift from Hg reduction toward Hg0 re-oxidation controlled by competitive ligand exchange. These results suggested that VB9 application significantly raised the potential for bacterial Hg methylation and cellular accumulation, thus proposing insights into the biochemical behaviors of hazardous Hg in farming environments where vulnerable organisms are more possibly co-exposed to higher levels of Hg and VB9.

Parachlorometaxylenol stress caused multidrug-type antibiotic resistance genes proliferation via simultaneously reshaping microbial community and interfering metabolic traits during wastewater treatment process

Despite biological wastewater treatment processes (e.g., sequencing batch reactors (SBR)) being able to reduce the dissemination of antibiotic resistance genes (ARGs), the variation of ARGs under exogenous pollutant stress is an open question. This work investigated the impacts of para-chloro-meta-xylenol (PCMX, typical antibacterial contaminants) on ARGs spread in long-term SBR operation. Although the SBR process inherently decreased ARGs abundance, the presence of PCMX substantially amplified both the prevalence (mainly multidrug) and abundance of total ARGs (1.17-fold of the control). Further analysis demonstrated that PCMX disintegrated sludge structures as well as increased membrane permeability, facilitating the release of mobile genetic elements and subsequent horizontal transfer of ARGs. In addition, PCMX selectively enriched potential ARG hosts, notably Nitrospira and Candidatus Accumulibacter, which predominantly served as multidrug ARG hosts. Concurrently, the self-adaptive functions of ARGs hosts in the PCMX-exposed SBR system were activated via quorum sensing, two-component regulatory system, ATP-binding cassette transporters, and bacterial secretion system. The upregulation of these metabolic pathways also contributed to the dissemination of ARGs.

How can the microbial community in watershed sediment maintain its resistance in the presence of shifting antibiotic residuals?

The widespread presence of antibiotics in global watershed environments poses a serious threat to public health and ecosystems. It is essential to examine the resistance of microbial communities in watershed environments in response to shifting antibiotic residues. Sediment samples were collected from seven sites across a watershed, encompassing surface sediment (0-10 cm) and bottom sediment (30-40 cm) depths. The aim was to replicate exposure scenarios to different antibiotics (oxytetracycline (OTC) and sulfadiazine (SD)) at varying concentrations (0, 10, and 100 μg/L) in sediment overlying water, within controlled laboratory settings. The study findings revealed significant variations in the microbial community structure of sediments between different treatments, with distinct differences observed in the upper stream and top sediment layers compared to the sediments located downstream and in the bottom layers. After the introduction of antibiotics, a significant decrease in microbial nodes was observed in the genus-level co-occurrence network analysis of the bottom sediment layer, particularly in the OTC treatment groups. In contrast, the downstream region displayed more robust correlations among the top 20 genera than the upstream area. There was no significant variance observed in the expression of Antibiotic resistance genes (ARGs), consisting of tetracycline resistance genes (tetC, tetG, tetM, tetW, and tetX) and sulfonamide resistance genes (sul1, sul2, and sul3), between sediments in the top and bottom layers. Nevertheless, downstream samples exhibited significantly higher levels of ARGs when compared to upstream samples. Network correlation analysis indicated notably lower correlations between ARGs and bacterial genera in sediments from upstream or surface layers compared to those in downstream or deeper layers. Moreover, correlations in the sediments from surface layers and upstream regions showed a decreasing trend with increasing SD exposure concentrations, while those in deeper layers and downstream areas remained relatively stable. The presence of antibiotics notably enhanced the correlation between sediment properties and ARGs, particularly emphasizing associations with total carbon, nitrogen, and sulfur content. However, the introduction of SD and OTC resulted in a decrease in the influence of these sediment factors on microbial community functions related to sulfur and nitrogen metabolism, as indicated by KEGG (Kyoto Encyclopedia of Genes and Genomes) annotation. The research provided empirical evidence on how microbial resistance responds to changes in antibiotics in sediment samples taken from various depths and locations within a watershed. It emphasized the urgent need for heightened awareness of the movement and alteration of antibiotic resistance patterns in watershed ecosystems.

Dietary lauric acid promoted antioxidant and immune capacity by improving intestinal structure and microbial population of swimming crab (Portunus trituberculatus)

Lauric acid (LA), a saturated fatty acid with 12 carbon atoms, is widely regarded as a healthy fatty acid that plays an important role in disease resistance and improving immune physiological function. The objective of this study was to determine the effects of dietary lauric acid on the growth performance, antioxidant capacity, non-specific immunity and intestinal microbiology, and evaluate the potential of lauric acids an environmentally friendly additive in swimming crab (Portunus trituberculatus) culture. A total of 192 swimming crabs with an initial body weight of 11.68 ± 0.02 g were fed six different dietary lauric acid levels, the analytical values of lauric acid were 0.09, 0.44, 0.80, 1.00, 1.53, 2.91 mg/g, respectively. There were four replicates per treatment and 8 juvenile swimming crabs per replicate. The results indicated that final weight, percent weight gain, specific growth rate, survival and feed intake were not significantly affected by dietary lauric acid levels; however, crabs fed diets with 0.80 and 1.00 mg/g lauric acid showed the lowest feed efficiency among all treatments. Proximate composition in hepatopancreas and muscle were not significantly affected by dietary lauric acid levels. The highest activities of amylase and lipase in hepatopancreas and intestine were found at crabs fed diet with 0.80 mg/g lauric acid (P < 0.05), the activity of carnitine palmityl transferase (CPT) in hepatopancreas and intestine significantly decreased with dietary lauric acid levels increasing from 0.09 to 2.91 mg/g (P < 0.05). The lowest concentration of glucose and total protein and the activity of alkaline phosphatase in hemolymph were observed at crabs fed diets with 0.80 and 1.00 mg/g lauric acid among all treatments. The activity of GSH-Px in hepatopancreas significantly increased with dietary lauric acid increasing from 0.09 to 1.53 mg/g, MDA in hepatopancreas and hemolymph was not significantly influenced by dietary lauric acid levels. The highest expression of cat and gpx in hepatopancreas were exhibited in crabs fed diet with 1.00 mg/g lauric acid, however, the expression of genes related to the inflammatory signaling pathway (relish, myd88, traf6, nf-κB) were up-regulated in the hepatopancreas with dietary lauric acid levels increasing from 0.09 to 1.00 mg/g, moreover, the expression of genes related to intestinal inflammatory, immune and antioxidant were significantly affected by dietary lauric acid levels (P < 0.05). Crabs fed diet without lauric acid supplementation exhibited higher lipid drop area in hepatopancreas than those fed the other diets (P < 0.05). The expression of genes related to lipid catabolism was up-regulated, however, and the expression of genes related to lipid synthesis was down-regulated in the hepatopancreas of crabs fed with 0.80 mg/g lauric acid. Lauric acid improved hepatic tubular integrity, and enhanced intestinal barrier function by increasing peritrophic membrane (PM) thickness and upregulating the expression of structural factors (per44, zo-1) and intestinal immunity-related genes. In addition, dietary 1.00 mg/g lauric acid significantly improved the microbiota composition of the intestinal, increased the abundance of Actinobacteria and Rhodobacteraceae, and decreased the abundance of Vibrio, thus maintaining the microbiota balance of the intestine. The correlation analysis showed that there was a relationship between intestinal microbiota and immune-antioxidant function. In conclusion, the dietary 1.00 mg/g lauric acid is beneficial to improve the antioxidant capacity and intestinal health of swimming crab.

Microbial community structure in a constructed wetland based on a recirculating aquaculture system: Exploring spatio-temporal variations and assembly mechanisms

The diversity, composition and performance of microbial communities within constructed wetlands (CW) were markedly influenced by spatio-temporal variations. A pilot-scale integrated vertical-flow constructed wetland (IVCW) as the biological purification unit within a recirculating aquaculture system (RAS) was established and monitored in this study. The investigation aimed to elucidate the responses of community structure, co-occurrence networks, and assembly mechanisms of the microbial community to spatial and temporal changes. Spatially, all a-diversity indices and microbial networks complexity were significantly higher in the upstream pool of the IVCW than in the downstream pool. Temporally, the richness increased over time, while the evenness showed a decreasing trend. The number of nodes and edges of microbial networks increased over time. Notably, the stable pollutant removal efficiencies were observed during IVCW operations, despite a-diversity and bacterial community networks exhibited significant variations across time. Functional redundancy emerged as a likely mechanism contributing to the stability of microbial ecosystem functions. Null model and neutral model analyses revealed the dominance of deterministic processes shaping microbial communities over time, with deterministic influences being more pronounced at lower a-diversity levels. DO and inorganic nitrogen emerged as the principal environmental factor influencing microbial community dynamics. This study provides a theoretical foundation for the regulation of microbial communities and environmental factors within the context of IVCW.

Bacterial community in the metal(loid)-contaminated marine vertical sediments of Jinzhou Bay: Impacts and adaptations

Metal(loid) discharge has led to severe coastal contamination; however, there remains a significant knowledge gap regarding its impact on sediment profiles and depth-resolved bacterial communities. In this study, geochemical measurements (pH, nutrient elements, total and bioavailable metal(loid) content) consistently revealed decreasing nitrogen, phosphorus, and metal(loid) levels with sediment depth, accompanied by reduced alpha diversity. Principal coordinate analysis indicated distinct community compositions with varying sediment depths, suggesting a geochemical influence on diversity. Ecological niche width expanded with depth, favoring specialists over generalists, but both groups decreased in abundance. Taxonomic shifts emerged, particularly in phyla and families, correlated with sediment depth. Microbe-microbe interactions displayed intricate dynamics, with keystone taxa varying by sediment layer. Zinc and arsenic emerged as key factors impacting community diversity and composition using random forest, network analysis, and Mantel tests. Functional predictions revealed shifts in potential phenotypes related to mobile elements, biofilm formation, pathogenicity, N/P/S cycles, and metal(loid) resistance along sediment profiles. Neutral and null models demonstrated a transition from deterministic to stochastic processes with sediment layers. This study provides insights into the interplay between sediment geochemistry and bacterial communities across sediment depths, illuminating the factors shaping these ecosystems.

Antibiotic resistance genes profile in the surface sediments of typical aquaculture areas across 15 major lakes in China

Aquatic farming is considered as a major source of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) for the natural environment of the lakes. ARB and ARGs in the natural environment have increased quickly because of the human activities. Here, we have profiled the diversity and abundance of ARGs in sediments from the typical aquaculture areas around 15 major lakes in China using PCR and qPCR, and further assessed the risk factor shaping the occurrence and distribution of ARGs. And class 1, 2 and 3 integrons were initially detected by PCR with specific primers. ARGs were widely distributed in the lakes: Weishan Lake and Poyang Lake showed high diversity of ARGs, followed by Dongting Lake, Chao Lake and Tai Lake. Generally, the ARGs in the Middle-Lower Yangtze Plain were more abundant than those in the Qinghai-Tibet Plateau. Tetracycline resistance genes (tet(C), tet(A) & tet(M)) were prominent in sediments, and the next was AmpC β-lactamase gene group BIL/LAT/CMY, and the last was the genes resistance to aminoglycoside (strA-strB). Partial least squares path modeling analysis (PLS-PMA) revealed that livestock had a significant direct effect on the distribution of ARGs in lakes, and population might indirectly influence the profiles of ARGs by affecting the scale of livestock and aquaculture. The detectable rate of class 1, 2 and 3 integrons were 80%, 100% and 46.67%, respectively. The prevalence of integrons might play a key role in promoting more frequent horizontal gene transfer (HGT) events, resulting in the environmental mobilization and dissemination of ARGs between bacteria.

Mapping the profiles and underlying driving mechanisms of the antibiotic resistome and microbiome within a subtropical complex river watershed

Antibiotic resistance is an escalating global concern, leading to millions of annual deaths worldwide. Human activities can impact antibiotic resistance gene (ARG) prevalence in aquatic ecosystems, but the intricate interplay between anthropogenic disturbances and river system resilience, and their respective contributions to the dynamics of different river segments, remains poorly understood. In this study, we investigate the antibiotic resistome and microbiome in water and sediment samples from two distinct sub-watersheds within a specific watershed. Results show a decrease in the number of core ARGs downstream in water, while sediments near densely populated areas exhibit an increase. PCoA ordination reveals clear geographic clustering of resistome and microbiome among samples from strong anthropogenic disturbed areas, reservoir areas, and estuary area. Co-occurrence networks highlight a higher connectivity of mobile genetic elements (MGEs) in disturbed areas compared to reservoir areas, presenting a threat to densely populated areas. Water quality parameters and antibiotics concentration were the key factors shaping the ARG profiles in sediment samples from urban regions. Overall, our study reveals distinct patterns of ARGs in sediment and water samples, emphasizing the importance of considering both anthropogenic and natural factors in comprehending and managing ARG distribution in river systems.

Microplastics shape microbial interactions and affect the dissemination of antibiotic resistance genes in different full-scale wastewater treatment plants

Wastewater treatment plants (WWTPs) pose a potential threat to the environment because of the accumulation of antibiotic resistance genes (ARGs) and microplastics (MPs). However, the interactions between ARGs and MPs, which have both indirect and direct effects on ARG dissemination in WWTPs, remain unclear. In this study, spatiotemporal variations in different types of MPs, ten ARGs (sul1, sul2, tetA, tetO, tetM, tetX, tetW, qnrS, ermB, and ermC), class 1 integron integrase (intI1) and transposon Tn916/1545 in three typical WWTPs were characterized. Sul1, tetO, and sul2 were the predominant ARGs in the targeted WWTPs, whereas the intI1 and transposon Tn916/1545 were positively correlated with most of the targeted ARGs. Saccharimonadales (4.15 %), Trichococcus (2.60 %), Nitrospira (1.96 %), Candidatus amarolinea (1.79 %), and SC-I-84 (belonging to phylum Proteobacteria) (1.78 %) were the dominant genera. Network and redundancy analyses showed that Trichococcus, Faecalibacterium, Arcobacter, and Prevotella copri were potential hosts of ARGs, whereas Candidatus campbellbacteria and Candidatus kaiserbacteria were negatively correlated with ARGs. The potential hosts of ARGs had a strong positive correlation with polyethylene terephthalate, silicone resin, and fluor rubber and a negative correlation with polyurethane. Candidatus campbellbacteria and Candidatus kaiserbacteria were positively correlated with polyurethane, whereas potential hosts of ARGs were positively correlated with polypropylene and fluor rubber. Structural equation modeling highlighted that intI1, transposon Tn916/1545 and microbial communities, particularly microbial diversity, dominated the dissemination of ARGs, whereas MPs had a significant positive correlation with microbial abundance. Our study deepens the understanding of the relationships between ARGs and MPs in WWTPs, which will be helpful in designing strategies for inhibiting ARG hosts in WWTPs.

Impacts of net cages on pollutant accumulation and its consequence on antibiotic resistance genes (ARGs) dissemination in freshwater ecosystems: Insights for sustainable urban water management

There has been increasing interest in the role of human activities in disseminating antibiotic-resistance genes (ARGs) in aquatic ecosystems. However, the influence of pollutant accumulation on anthropogenic pollutant-ARG synergistic actions is limited. This study explored the association of net cages with the propagation of anthropogenic pollutants and their consequences for influencing the enrichment of ARGs using high-throughput metagenomic sequencing. We showed that net cages could substantially impact the ecology of freshwater systems by enhancing i) ARG diversity and the tendency for ARG-horizontal gene transfer and ii) the overlap of mobile genetic elements (MGEs) with biocide-metal resistance genes (BMRGs) and ARGs. These findings suggested that the cotransfer of these three genetic determinants would be favored in net cage plots and that nonantibiotic factors such as metal(loid)s, particularly iron (Fe), displayed robust selective pressures on ARGs exerted by the net cage. The resistome risk scores of net cage sediments and biofilms were higher than those from off-net cage plots, indicating that the net cage-origin antibiotic resistome should be of great concern. The combination of deterministic and stochastic processes acting on bacterial communities could explain the higher ARG variations in cage plots (8.2%) than in off-cage plots (3.4%). Moreover, MGEs and pollutants together explained 43.3% of the total variation in ARG communities, which was higher than that of off-cage plots (8.8%), considering pollutants, environmental variables, MGEs, and assembly processes. These findings will inform the development of policies and guidelines to more effectively limit the spread of antimicrobial resistance and achieve the goal of sustainability in freshwater systems in urban areas.

Unraveling the interplay between antibiotic resistance genes and microbial communities in water and sediments of the intensive tidal flat aquaculture

Tidal flats are formed valuably resources by the interaction of terrestrial and marine processes. Aquaculture on tidal flats has brought significant economic profits, but the over usage of antibiotics has resulted in the prevalence antibiotic resistance genes (ARGs) which pose serious threats to ecosystems. However, ARG abundances and bacterial community assemblies in the overlying water and sediments of tidal flat aquaculture areas have not been fully explored. Thus, antibiotic concentrations, ARG abundances, microbial communities and the influences of environmental factors in the Jiangsu tidal flat aquaculture ponds were investigated using high-throughput sequencing and qPCR. The concentrations of antibiotics at sampling ranged from not detectable to 2322.4 ng g-1, and sulfamethazine and ciprofloxacin were the dominant antibiotics. The sul1 and sul2 abundances were highest and the ARG abundances were higher in sediment than in water. Meanwhile, bacterial community diversities and structures were significantly different (P < 0.05) between water and sediment samples. Network analysis identified Sphingomonadacear, Pseudomonas, and Xanthobacteraceae as potential ARG-carrying pathogens. A positive correlation between ARGs and intI1 indicated that horizontal gene transfer occurred in water, while antibiotics and TN significantly influenced ARG abundances in sediment. Neutral modeling showed that deterministic and stochastic processes contributed most to the bacterial community assemblies of water and sediment samples, respectively. This study comprehensively illustrates the prevalence of ARGs in intensive tidal flat aquaculture regions and provides an effective foundation for the management of antibiotics usage.

Gross yield driving the mass fluxes of fishery drugs: Evidence of occurrence from full aquaculture cycle in lower Yangtze River Basin

Expanding aquaculture has generated pollutants like fishery drugs in wastewater, which affects the aquatic environments and hinders sustainable development of aquaculture. To evaluate the occurrence, mass fluxes and production factors of fishery drugs in aquaculture, full-aquaculture-cycle monitoring in finfish and crustacean wastewater was conducted in the lower Yangtze River Basin, and 28 pesticides and 15 antibiotics were detected. The results showed that individual fishery drugs varied from ppt to ppb levels. Among them, sulfonamides were dominant with a mean concentration of 105.95 ± 4.13 ng·L-1 in finfish aquacultural wastewater, and insecticides were prevailing in crustacean aquacultural wastewater with a content of 146.56 ± 0.66 ng·L-1. Since the susceptibility to finfish disease determined the aquaculture practice, there were significant differences between two types of aquacultural wastewater. Finfish aquacultural wastewater contained more drugs and reached peak earlier in rapid-growth period, yet crustacean aquacultural wastewater peaked at the harvest period, to prevent against disease. Meanwhile, higher ecological risk, especially for florfenicol, were found in finfish wastewater. With 6 production factors from Good Aquaculture Practice, the gross yield was the most influential factor of drug mass flux, explaining 98 % variance by stepwise regression. Apart from increasing concentrations of fishery drugs in wastewater, regional high-yield aquaculture also significantly impacted the corresponding mass flux. As estimated by linear regression, 1.63 tons of target drugs would be discharged by 1 Mt. aquatic products, and 7.77 tons were discharged from aquaculture in the lower Yangtze River Basin in 2021. This is the first report to quantify mass fluxes of fishery drugs and to highlight gross yield as the most influential factor, which provides guidance for the supervision and regulation of sustainable aquaculture.

Concentrations, distribution, and key influencing factors of antibiotic resistance genes and bacterial community in water and reared fish tissues in a typical tilapia farm in South China

Although previous studies have investigated the occurrence of antibiotic resistance genes (ARGs) in aquaculture, few have monitored the concentrations and propagation of ARGs in biological tissues or investigated the key factors influencing their spread in aquaculture. This study investigated the concentration, propagation, and distribution of ARGs and bacterial communities in water sources, pond water, and tilapia tissues, and their key influencing factors, in a typical tilapia farm. ErmF, sul1, and sul2 were the dominant ARGs with high concentrations. The total concentrations of ARGs (TCAs) in tilapia tissues decreased in the following order: stomach > scales > intestine > gills (P < 0.05). Redundancy analysis and multiple linear regression revealed that suspended solids (SS) and chemical oxygen demand (COD) were positively correlated with the dominant ARGs ermF sul2, and the TCAs (P < 0.05); additionally, Chloroflexi and Bacteroidetes in tilapia aquaculture water were positively correlated with the dominant ARGs ermF and sul2, as well as the TCAs (P < 0.05). This study suggests that SS and COD were the key factors driving the distribution and spread of ARGs in tilapia aquaculture water. Additionally, Chloroflexi and Bacteroidetes were the key bacterial flora affecting the propagation of ARGs in tilapia aquaculture systems.

Profiles and spatial distributions of heavy metals, microbial communities, and metal resistance genes in sediments from an urban river

The occurrence and propagation of resistance genes due to exposure to heavy metals (HMs) in rivers is an emerging environmental issue. Little is known about resistance genes in microbial communities in river sediments with low HM concentrations. The profiles and spatial distributions of HMs, the microbial community, and metal resistance genes (MRGs) were analyzed in sediment samples from the Zhilong River basin in Yangjiang city, near the Pearl River Delta. Concentrations of copper (Cu), cadmium (Cd), lead (Pb), chromium (Cr), and nickel (Ni) were relatively low compared with those in other urban river sediments in China. HM chemical composition and fractions and the structure of the microbial community varied along the main channel, but the composition and abundance of MRGs were relatively homogeneous. Variations in HMs and microbial communities in mid- to upstream areas were related to the presence of tributaries, whose inputs were one of the major factors affecting HM chemical fractions and genera structure in mainstream sediments. There were no significant correlations (p < 0.05) between HM concentrations, bacterial communities, and the MRG profiles; thus, HM concentrations were not the main factor affecting MRGs in sediments. These results contribute to understanding the propagation of MRGs in urban rivers in developing cities.

Insight into the spatiotemporal distribution of antibiotic resistance genes in estuarine sediments during long-term ecological restoration

In this study, we aimed to investigate the long-term spatiotemporal changes in hydrodynamics, antibiotics, nine typical subtypes of antibiotic resistance genes (ARGs), class 1 integron gene (intI1), and microbial communities in the sediments of a semi-enclosed estuary during ecological restoration with four treatment stages (influent (#1), effluent of the biological treatment area (#2), oxic area (#3), and plant treatment area (#4)). Ecological restoration of the estuary reduced common pollutants (nitrogen and phosphorus) in the water, whereas variations in ARGs showed noticeable seasonal and spatial features. The absolute abundance of ARGs at sampling site #2 considerably increased in autumn and winter, while it significantly increased at sampling site #3 in spring and summer. The strong intervention of biological treatment (from #1 to #2) and aerators (from #2 to #3) in the estuary substantially affected the distribution of ARGs and dominant antibiotic-resistant bacteria (ARB). The dominant ARB (Thiobacillus) in estuarine sediments may have low abundance but important dissemination roles. Meanwhile, redundancy and network analysis revealed that the microbial communities and intl1 were key factors related to ARG dissemination, which was affected by spatial and seasonal ecological restoration. A positive correlation between low flow velocity and certain ARGs (tetM, tetW, tetA, sul2, and ermC) was observed, implying that flow optimization should also be considered in future ecological restoration to remediate ARGs. Furthermore, the absolute abundance of ARGs can be utilized as an index to evaluate the removal capacity of ARGs by estuarine restoration.

Distribution and drivers of antibiotic resistance genes in brackish water aquaculture sediment

Brackish water aquaculture has brought numerous economic benefits, whereas anthropogenic activities in aquaculture may cause the dissemination of antibiotic resistance genes (ARGs) in brackish water sediments. The intricate relationships between environmental factors and microbial communities as well as their role in ARGs dissemination in brackish water aquaculture remain unclear. This study applied PCR and 16S sequencing to identify the variations in ARGs, class 1 integron gene (intI1) and microbial communities in brackish water aquaculture sediment. The distribution of ARGs in brackish water aquaculture sediment was similar to that in freshwater aquaculture, and the sulfonamide resistance gene sul1 was the indicator of ARGs. Proteobacteria and Firmicutes were the dominant phyla, and Paenisporosarcina (p_ Firmicutes) was the dominant genus. The results of correlation, network and redundancy analysis indicated that the microbial community in the brackish water aquaculture sediment was function-driven. The neutral model and variation partitioning analysis were used to verify the ecological processes of the bacterial community. The normalized stochasticity ratio showed that pond bacteria community was dominated by determinacy, which was affected by aquaculture activities. The total nitrogen and organic matter influenced the abundance of ARGs, while Proteobacteria and Thiobacillus (p_Proteobacteria) were the key antibiotic-resistant hosts. Our study provides insight into the prevalence of ARGs in brackish water aquaculture sediments, and indicates that brackish water aquaculture is a reservoir of ARGs.

Estuarine Aquacultures at the Crossroads of Animal Production and Antibacterial Resistance: A Metagenomic Approach to the Resistome

It is recognized that the spread of antibiotic resistance (AR) genes among aquatic environments, including aquaculture and the human environment, can have detrimental effects on human and animal health and the ecosystem. Thus, when transmitted to the human microbiome or pathogens, resistance genes risk human health by compromising the eventual treatment of infections with antibiotic therapy. This study aimed to define the resistance profile of aquaculture farms and their potential risk for spreading. Twenty-four sediments from oyster and gilthead sea bream aquaculture farms located in three Portuguese river estuaries (17 sediments from Sado, 4 from Aveiro, and 3 from Lima) were studied by comparative metagenomic analysis. The computation of the diversity of genes conferring resistance per antibiotic class revealed a significant increase in aminoglycosides, beta-lactams, disinfectants, quinolones, and tetracyclines counts. In all geographic locations under study, the most diverse AR genes confer resistance to the macrolides, tetracyclines and oxazolidinones classes, all of which are medically important for human and animal therapies, as well as resistance to disinfectants. The diversity of mobile genetic elements correlated with the number of AR genes such as tetracyclines, suggesting that AR could be easily mobilized among bacterial genomes and microbiomes.