Antibiotic Resistance Genes In Soil Research Articles

Impact of earthworms on antibiotic resistance genes removal in ampicillin-contaminated soil through bacterial community alteration.

The emergence of antibiotic resistance genes (ARGs) as contaminants in soil poses a significant threat to public health. Earthworms (Eisenia foetida), which are common inhabitants of soil, have been extensively studied for their influence on ARGs. However, the specific impact of earthworms on penicillin-related ARGs remains unclear. In this study, we investigate the role of earthworms in mitigating ARGs, specifically penicillin-related ARGs, in ampicillin-contaminated soil. Utilizing high-throughput quantitative PCR (HT-qPCR), we quantified a significant reduction in the relative abundance of penicillin-related ARGs in soil treated with earthworms, showing a decrease with a p-value of <0.01. Furthermore, high-throughput 16S rRNA gene sequencing revealed that earthworm intervention markedly alters the microbial community structure, notably enhancing the prevalence of specific bacterial phyla such as Proteobacteria, Firmicutes, Chloroflexi, and Tenericutes. Our findings not only demonstrate the effectiveness of earthworms in reducing the environmental load of penicillin-related ARGs but also provide insight into the alteration of microbial communities as a potential mechanism. This research contributes to our understanding of the role of earthworms in mitigating the spread of antibiotic resistance and provides valuable insights for the development of strategies to combat this global health issue.

Body size: A hidden trait of the organisms that influences the distribution of antibiotic resistance genes in soil

Body size is a key life-history trait of organisms, which has important ecological functions. However, the relationship between soil antibiotic resistance gene (ARG) distribution and organisms' body size has not been systematically reported so far. Herein, the impact of organic fertilizer on the soil ARGs and organisms (bacteria, fungi, and nematode) at the aggregate level was analyzed. The results showed that the smaller the soil aggregate size, the greater the abundance of ARGs, and the larger the body size of bacteria and nematodes. Further analysis revealed significant positive correlations of ARG abundance with the body sizes of bacteria, fungi, and nematodes, respectively. Additionally, the structural equation model demonstrated that changes in soil fertility mainly regulate the ARG abundance by affecting bacterial body size. The random forest model revealed that total phosphorus was the primary soil fertility factor influencing the body size of organisms. Therefore, these findings proposed that excessive application of phosphate fertilizers could increase the risk of soil ARG transmission by increasing the body size of soil organisms. This study highlights the significance of organisms' body size in determining the distribution of soil ARGs and proposes a new disadvantage of excessive fertilization from the perspective of ARGs.

Linking bacterial life strategies with the distribution pattern of antibiotic resistance genes in soil aggregates after straw addition

Straw addition markedly affects the soil aggregates and microbial community structure. However, its influence on the profile of antibiotic resistance genes (ARGs), which are likely associated with changes in bacterial life strategies, remains unclear. To clarify this issue, a soil microcosm experiment was incubated under aerobic (WS) or anaerobic (AnWS) conditions after straw addition, and metagenomic sequencing was used to characterise ARGs and bacterial communities in soil aggregates. The results showed that straw addition shifted the bacterial life strategies from K- to r-strategists in all aggregates, and the aerobic and anaerobic conditions stimulated the growth of aerobic and anaerobic r-strategist bacteria, respectively. The WS decreased the relative abundances of dominant ARGs such as QnrS5, whereas the AnWS increased their abundance. After straw addition, the macroaggregates consistently exhibited a higher number of significantly altered bacteria and ARGs than the silt+clay fractions. Network analysis revealed that the WS increased the number of aerobic r-strategist bacterial nodes and fostered more interactions between r-and K-strategist bacteria, thus promoting ARGs prevalence, whereas AnWS exhibited an opposite trend. These findings provide a new perspective for understanding the fate of ARGs and their controlling factors in soil ecosystems after straw addition. Environmental implicationsStraw soil amendment has been recommended to mitigate soil fertility degradation, improve soil structure, and ultimately increase crop yields. However, our findings highlight the importance of the elevated prevalence of ARGs associated with r-strategist bacteria in macroaggregates following the addition of organic matter, particularly fresh substrates. In addition, when assessing the environmental risk posed by ARGs in soil that receives crop straw, it is essential to account for the soil moisture content. This is because the species of r-strategist bacteria that thrive under aerobic and anaerobic conditions play a dominant role in the dissemination and accumulation of ARG.

Assessment of antibiotic resistance genes in soils polluted by chemical and technogenic ways with poly-aromatic hydrocarbons and heavy metals

Anthropogenic activities are leaving lots of chemical footprints on the soil. It alters the physiochemical characteristics of the soil thereby modifying the natural soil microbiome. The prevalence of antimicrobial-resistance microbes in polluted soil has gained attention due to its obvious public health risks. This study focused on assessing the prevalence and distribution of antibiotic-resistance genes in polluted soil ecosystems impacted by industrial enterprises in southern Russia. Metagenomic analysis was conducted on soil samples collected from polluted sites using various approaches, and the prevalence of antibiotic-resistance genes was investigated. The results revealed that efflux-encoding pump sequences were the most widely represented group of genes, while genes whose products replaced antibiotic targets were less represented. The level of soil contamination increased, and there was an increase in the total number of antibiotic-resistance genes in proteobacteria, but a decrease in actinobacteria. The study proposed an optimal mechanism for processing metagenomic data in polluted soil ecosystems, which involves mapping raw reads by the KMA method, followed by a detailed study of specific genes. The study's conclusions provide valuable insights into the prevalence and distribution of antibiotic-resistance genes in polluted soils and have been illustrated in heat maps.

Distribution, source apportionment, and ecological risk assessment of soil antibiotic resistance genes in urban green spaces

Urban green spaces play a crucial role in cities by providing near-natural environments that greatly impacts the health of residents. However, these green spaces have recently been scrutinized as potential reservoirs of antibiotic resistance genes (ARGs), posing significant ecological risks. Despite this concern, our understanding of the distribution, sources, and ecological risks associated with ARGs remains limited. In this study, we investigated the spatial distribution of soil ARGs using spatial interpolation and auto-correlation analysis. To apportion the source of soil ARGs in urban green spaces of Tianjin, Geo-detector method (GDM) was employed. Furthermore, we evaluated the ecological risk posed by ARGs employing risk quotients (RQ). The results of our study showed a significantly higher abundance of Quinolone resistance genes in the soil of urban green spaces in Tianjin. These genes were mainly found in the northwest, central, and eastern regions of the city. Our investigation identified three main factors contributing to the presence of soil ARGs: antibiotic production, precipitation, livestock breeding, and hospital. The results of ecological risk in RQ value showed a high risk associated with Quinolone resistance genes, followed by Aminoglycoside, Tetracycline, Multidrug, MLSB, Beta Lactam, Sulfonamide, and Chloramphenicol. Mantel-test and correlation analysis revealed that the ecological risk of ARGs was greatly influenced by soil properties and heavy metals. This study provides a new perspective on source apportionment and the ecological risk assessment of soil ARGs in urban green spaces.

Food waste compost and digestate as novel fertilizers: Impacts on antibiotic resistome and potential risks in a soil-vegetable system

As a novel agricultural practice, the reuse of food waste compost and digestate as fertilizers leads to a circular economy, but inevitably introduces bio-contaminants such as antibiotic resistance genes (ARGs) into the agroecosystem. Moreover, heavy metal and antibiotic contamination in farmland soil may exert selective pressures on the evolution of ARGs, posing threats to human health. This study investigated the fate, influencing mechanisms and potential risks of ARGs in a soil-vegetable system under different food waste fertilization and remediation treatments and soil contamination conditions. Application of food waste fertilizers significantly promoted the pakchoi growth, but resulted in the spread of ARGs from fertilizers to pakchoi. A total of 56, 80, 84, 41, and 73 ARGs, mobile genetic elements (MGEs) and metal resistance genes (MRGs) were detected in the rhizosphere soil (RS), bulk soil (BS), control soil (CS), root endophytes (RE), and leaf endophytes (LE), respectively. Notably, 7 genes were shared in the above five subgroups, indicating a specific soil-root-endophytes transmission pathway. 36 genes were uniquely detected in the LE, which may originate from airborne ARGs. The combined application of biochar and fertilizers reduced the occurrence of ARGs and MGEs to some extent, showing the remediation effect of biochar. The average abundance of ARGs in the RS, BS and CS was 3.15 × 10−2, 1.31 × 10−2 and 2.35 × 10−1, respectively. Rhizosphere effects may reduce the abundance of ARGs in soil. The distribution pattern of ARGs was influenced by the types of soil, endophyte and contaminant. MGEs is the key driver shaping ARGs dynamics. Soil properties and pakchoi growth status may affect the bacterial composition, and consequently regulate ARGs fate, while endophytic ARGs were more impacted by biotic factors. Moreover, the average daily doses of ARGs from pakchoi consumption is 107–109 copies/d/kg, and its potential health risks should be emphasized.

Effect of biochar on the fate of antibiotic resistant genes and integrons in compost amended agricultural soil.

The persistence and transmission of emerging pollutants such as antibiotic resistance genes (ARGs) via mobile genetic elements (MGEs) have caused concern to scientific community. Composting practises are often adapted for the reduction of organic waste or to enhance fertility in agriculture soil but its continuous usage has posed a potential risk of increased abundance of ARGs in soil. Thus, the present study scrutinises the emerging risk of ARGs and MGEs in agriculture soil and its potential mitigation using biochar owing to its proven environmental sustainability and performance. After 30days incubation, ARG distribution of SulI, SulII, dfrA1, dfrA12, tetA, flor, and ErmA was 50, 37.5, 37.5, 62.5, 42.11, 62.5, and 52.63% in control samples whereas it was 5, 15.78, 21.05, 15.79, 10.53, 21.05, and 31.58%, respectively, for biochar amended samples. Similarly, IntI1 and IntI2 in control and biochar amended samples were 18.75 and 6.25% and 10.53 and 5.26%, respectively. Principal component analysis (PCA) factor suggests that biochar amendment samples showed enhanced value for pH, organic matter, and organic carbon over control samples. Furthermore, Pearson's correlation analysis performed between detected ARGs and MGEs demonstrated the positive and significant correlation at p < 0.05 for both control and biochar amended samples.

Dissemination of antibiotic resistance genes is regulated by iron oxides: Insight into the influence on bacterial transformation

The transportation of antibiotic resistance genes (ARGs) in manure-soil-plant continuums poses risks to human health. Horizontal gene transfer, particularly for bacterial transformation, is an important way for ARG dissemination. As crucial components in soils, iron oxides impacted the fates of various abiotic and biotic contaminants due to their active properties. However, whether they can influence the transformation of ARGs is unknown, which waits to be figured out to boost the assessment and control of ARG spread risks. In this study, we have investigated the effects of goethite, hematite, and magnetite (0–250 mg/L, with sizes < 100 nm and > 100 nm) on the transfer of ampicillin resistance genes to Escherichia coli cells. At lower iron oxide concentrations, the transformation of ARGs was first facilitated (transformation frequency reached up to 3.38-fold higher), but the facilitating effects gradually weakened and eventually disappeared as concentrations further increased. Particle size and iron oxide type were not the universal determinants controlling the transformation. At lower concentrations, iron oxides interacted with proteins and phospholipids in E. coli envelope structures, and induced the overgeneration of intracellular reactive oxygen species. Consequently, they led to pore formation and permeability enhancement on the cell membrane, thus promoting the transformation. The facilitation was also associated with the carrier-like effect of iron oxides for antibiotic resistance plasmids. At higher concentrations, the weakened facilitations were attributed to the aggregation of iron oxides. In this study, we highlight the crucial roles of the concentrations (contents) of iron oxides on the dissemination of ARGs in soils; this study may serve as a reference for ARG pollution control in future agricultural production.

Effects of reductive soil disinfestation on potential pathogens and antibiotic resistance genes in soil

Reductive soil disinfestation (RSD) is commonly employed for soil remediation in greenhouse cultivation. However, its influence on antibiotic resistance genes (ARGs) in soil remains uncertain. This study investigated the dynamic changes in soil communities, potential bacterial pathogens, and ARG profiles under various organic material treatments during RSD, including distillers’ grains, potato peel, peanut vine, and peanut vine combined with charcoal. Results revealed that applying diverse organic materials in RSD significantly altered bacterial community composition and diminished the relative abundance of potential bacterial pathogens (P < 0.05). The relative abundance of high-risk ARGs decreased by 10.7%-30.6% after RSD treatments, the main decreased ARG subtypes were AAC(3)_Via, dfrA1, ErmB, lnuB, aadA. Actinobacteria was the primary host of ARGs and was suppressed by RSD. Soil physicochemical properties, such as total nitrogen, soil pH, total carbon, were crucial factors affecting ARG profiles. Our findings demonstrated that RSD treatment inhibited pathogenic bacteria and could be an option for reducing high-risk ARG proliferation in soil.

Effect of wheat crops on the persistence and attenuation of antibiotic resistance genes in soil after swine wastewater application

Swine wastewater (SW) application introduces antibiotic resistance genes (ARGs) into farmland soils. However, ARG attenuation in SW-fertigated soils, especially those influenced by staple crops and soil type, remains unclear. This study investigated twelve soil ARGs and one mobile genetic element (MGE) in sandy loam, loam, and silt loam soils before and after SW application in wheat-planted and unplanted soils. The results revealed an immediate increase in the abundance of ARGs in soil by two orders of magnitude above background levels following SW application. After SW application, the soil total ARG abundance was attenuated, reaching background levels at 54 days; However, more individual ARGs were detected above the detection limit than pre-application. Among the 13 genes, acc(6′)-lb, tetM, and tetO tended to persist in the soil during wheat harvest. ARG half-lives were up to four times longer in wheat-planted soils than in bare soils. Wheat planting decreased the persistence of acc(6′)-lb, ermB, ermF, and intI2 but increased the persistence of others such as sul1 and sul2. Soil type had no significant impact on ARG and MGE fates. Our findings emphasize the need for strategic SW application and the consideration of crop cultivation effects to mitigate ARG accumulation in farmland soils.

The effects of cadmium-copper stress on the accumulation of antibiotic-resistance genes in soil and pakchoi leaves

Antibiotic resistance and heavy metal contamination are two worldwide environmental concerns. Especially in soil, the interaction between these two pollutants may exacerbate the problem of antibiotic resistance genes (ARGs) entering the food chain, which can have severe consequences on the environment and the wellness of humankind. This study investigated the influences of cadmium (Cd) and copper (Cu) pollution on ARG profiles in the soil rhizosphere and endogenous microbiome of roots and leaves in pakchoi. We further determined the impact of these heavy metals and various environmental factors on the accumulation of ARGs in leaves and discussed the possible transfer pathways of ARGs in the soil-plant system. Our results showed that Cd–Cu stress increased the relative abundance of most target genes in the samples, especially the sulfonamide resistance genes sul1 and sul3, the quinolone resistance gene qepA, and the Class 1 integron integrase gene intI1. Variance partitioning analysis indicated that the Cd–Cu contents primarily contributed (45.7%) to ARG variations in leaves. Cadmium and Cu led to a pollution-induced community tolerance phenomenon in microbial communities, enriching Cd- and Cu-tolerant bacteria. ARGs were highly correlated with mobile genetic elements (e.g., intI1) and metal resistance genes, increasing the co-selection of metals on ARGs. Structural equation modeling showed that metal resistance genes and intI1 in leaves had significant direct positive effects on the relative abundances of ARGs (p < 0.05). Higher Cu concentrations facilitated the migration of most target ARGs from soil to leaves.

Environmental factors dominate microbial community puppet-like driving the distribution of antibiotic resistance genes in different utilization lands

Excessive use of antibiotics has caused the accumulation of antibiotic resistance genes (ARGs) in the soil environment, posing a great challenge to environmental safety and public health. However, there is a lack of comprehensive investigations of soil ARGs profiles under different land utilization patterns, and the drivers that affect the distribution of ARGs remain poorly defined. Herein, we investigated the ARGs profiles of eight different land uses and explored the critical factors influencing the distribution of ARGs. The results showed that ARGs abundance in soil of parks, residential areas, farmland, and vegetable cultivation was significantly higher than that in other lands, with an average of 2.08 × 103 copies/g dry soil. The structural equation model demonstrated that the environmental variables were the pivotal drivers that dominated the differences in ARG distribution across land utilization types (path coefficient=0.934), in which the physicochemical factors exhibited the greatest contribution with an explanatory rate of 20.27%, which was markedly higher than that of antibiotics and heavy metal residues. Importantly, these physicochemical factors manipulate the succession of microbial communities by altering the connections between microorganisms, which in turn indirectly affects the distribution of ARGs. Moreover, ARG exposure was strongly correlated with fertilizer application, precipitation, and per capita water resources (p < 0.01). Overall, this study provides a well-rounded understanding of ARG exposure under different land-use patterns, which helps to develop management strategies for curbing ARGs dissemination in the environment.

Thermokarst lakes are hotspots of antibiotic resistance genes in permafrost regions on the Qinghai-Tibet Plateau

Antibiotic resistance genes (ARGs) are natural products and emerging pollutants in remote environments, including permafrost regions that are rapidly thawing due to climate warming. We investigated the role of thermokarst lakes (including sediment and water) in reserving ARGs compared to permafrost soils across the permafrost regions on the Qinghai-Tibet Plateau. As intrinsically connected distinct environments, permafrost soil, lake sediment, and lake water harbored 1239 ARGs in total, while a considerable number of same ARGs (683 out of 1239) concurrently presented in all these environments. Soil and sediment had a higher number of ARGs than water. Multidrug resistance genes were the most diverse and abundant in all three environments, where cls, ropB, mdfA, fabI, and macB were the top five most abundant ARGs while with different orders. Soil and sediment had similar ARG profiles, and the alpha and beta diversity of ARGs in sediment were positively correlated with that in soil. The beta diversity of ARG profiles between sediment and soil was highly contributed by turnover component (89%). However, turnover and nestedness components were almost equality contributed (46%–54%) to the beta diversity of ARG profiles between soil and water as well as between sediment and water. The results suggested that thermokarst lake sediments might inherit the ARGs in permafrost soils. Water ARGs are the subset of soil ARGs and sediment ARGs to a certain degree with species turnover playing a significant role. When accounting the ARGs in sediment and water together, thermokarst lakes had a significantly higher number of ARGs than permafrost soils, suggesting that thermokarst lakes act as the hotspots of ARGs in permafrost regions. These findings are disturbing especially due to the fact that tremendous number of thermokarst lakes are forming under accelerating climate change.

Effects of anaerobic soil disinfestation on antibiotics, human pathogenic bacteria, and their associated antibiotic resistance genes in soil

Despite the widespread use of anaerobic soil disinfestation (ASD) to improve soil health, its impact on soil antibiotics, human pathogenic bacteria (HPB) and antibiotic resistance genes (ARGs) remains unclear. To address this knowledge gap, we conducted an incubation study in manure-amended soil with three treatments: no treatment (CK), crop straw only (CS), and CS combined with water flooding and plastic covering (ASD). The results showed that ASD increased the concentrations of tetracycline by 27 % and β-lactam by 22 %, while depleting macrolide by 51 %. Furthermore, ASD increased the numbers of potential HPB species and genes by 4.1 % and 23 %, respectively. Co-occurrence network analysis demonstrated intensified cooperation and competition among HPB and HNPB (human non-pathogenic bacteria) species under ASD, favoring the prevalence of HPB species such as Escherichia coli, Streptococcus equi, Clostridium tetani, and Bacillus anthracis. Potential HPB species in Proteobacteria exhibited negative correlations with macrolide and β-lactam antibiotics, whereas those in Firmicutes showed positive correlations with tetracycline antibiotics, suggesting that specific bacterial taxa contributed to the production and degradation of antibiotics in response to ASD. Interestingly, CS mitigated the presence of ARGs in soil, while ASD further amplified this reduction, almost eliminating nalC, acrB, OXA-60, VIM-7, tetL, and tetQ. The variation in ARG profiles (91.7 %) could be explained by antibiotics, HPB, and HNPB species, indicating their collective contribution to reducing soil ARGs under ASD. Moreover, host prediction and network analysis revealed that, compared with CK, where potential HPB species were the main carriers of ARGs, soil ARGs were less frequently carried by potential HPB species after ASD, indicating a reduction in the collaborative dissemination of HPB and ARGs in manured soil. In conclusion, ASD provides a promising strategy for mitigation of soil biologic contamination, which can have profound significance for environmental safety and agricultural sustainability.

Effects and mechanisms of polystyrene micro- and nano-plastics on the spread of antibiotic resistance genes from soil to lettuce

Effects of microplastics (MPs) and nanoplastics (NPs) on the spread of antibiotic resistance genes (ARGs) in soil-plant systems are still unclear. To investigate the spread and mechanisms of ARGs from soil to lettuce, lettuce was exposed to soil spiked with two environmentally relevant concentrations of polystyrene MPs (100 μm) and NPs (100 nm). Results showed that microorganisms that carried ARGs in soil were increased after exposure to MPs/NPs, which led to an increase in ARGs in roots. NPs were absorbed by roots and can be transported to leaves. Analysis of transcriptomics, proteomics and metabolomics indicated that high concentration of NPs regulated the expression of related genes and proteins and improved the accumulation of flavonoids in the lettuce, therefore decreased the abundance of microorganisms that contained ARGs. Our work emphasizes the size and dose influences of MPs and NPs on the spread of ARGs from soil to plant.

Evaluation of resistance risk in soil due to antibiotics during application of penicillin V fermentation residue

ABSTRACT The soil application of hydrothermally treated penicillin V fermentation residue (PFR) is attractive but challenged, due to the concern of the resistance risk in soil related to residual antibiotics. In this study, a lab-scale incubation experiment was conducted to investigate the influence of penicillin V on antibiotic resistance genes (ARGs) in PFR-amended soil via qPCR. The introduced penicillin V in soil could not be persistent, and its degradation occurred mainly within 2 days. The higher number of soil ARGs was detected under 108 mg/kg of penicillin V than lower contents (≤54 mg/kg). Additionally, the relative abundance of ARGs was higher in soil spiked with penicillin V than that in blank soil, and the great increase in the relative abundance of soil ARGs occurred earlier under 108 mg/kg of penicillin V than lower contents. The horizontal gene transfer might contribute to the shift of ARGs in PFR-amended soil. The results indicated that the residual penicillin V could cause the proliferation of soil ARGs and should be completely removed by hydrothermal treatment before soil application. The results of this study provide a comprehensive understanding of the resistance risk posed by penicillin V during the application of hydrothermally pretreated PFR.

Microbial organic fertilizer prepared by co-composting of Trichoderma dregs mitigates dissemination of resistance, virulence genes, and bacterial pathogens in soil and rhizosphere

The use of manure, mycelium dregs and other waste as organic fertilizer is the main source of antibiotic resistance genes (ARGs) and pathogens in farmland. Composting of waste may effectively remove ARGs and pathogens. However, the profiles and drivers of changes in metal resistance genes (MRGs), biocide resistance genes (BRGs), and virulence genes (VGs) in soil-crop rhizosphere systems after compost application remain largely unknown. Here, we prepared two kinds of microbial organic fertilizers (MOF) by using Trichoderma dregs (TDs) and organic fertilizer mixing method (MOF1) and TDs co-composting method (MOF2). The effects of different types and doses of MOF on resistance genes, VGs and pathogens in soil-rhizosphere system and their potential mechanisms were studied. The results showed that co-composting of TDs promoted the decomposition of organic carbon and decreased the absolute abundance of ARGs and mobile genetic elements (MGEs) by 53.4–65.0%. MOF1 application significantly increased the abundance and diversity of soil ARGs, BRGs, and VGs, while low and medium doses of MOF2 significantly decreased their abundance and diversity in soil and rhizosphere. Patterns of positive co-occurrence between MGEs and VGs/MRGs/BRGs/ARGs were observed through statistical analysis and gene arrangements. ARGs/MRGs reductions in MOF2 soil were directly driven by weakened horizontal gene transfer triggered by MGEs. Furthermore, MOF2 reduced soil BRGs/VGs levels by shifting bacterial communities (e.g., reduced bacterial host) or improving soil property. Our study provided new insights into the rational use of waste to minimize the spread of resistomes and VGs in soil.

Effects of chicken manure‐modified biochar on the adsorption capacity of tetracycline and abundance of antibiotic resistance genes in soil

AbstractLarge quantities of livestock manure not only occupy farmland but also serve as the primary source of antibiotics and antibiotic resistance genes (ARGs) in agricultural soil. To enhance the resource utilization of animal manure and mitigate ecological risks associated with antibiotics in agroecosystems, chicken manure was used as a raw material for biochar production. The manure derived biochar (MB) was modified with an alkali–acid two‐step modification process. The results showed that the total pore volume and surface area of alkali–acid modified MB (AMMB) was significantly increased about three and five times, respectively after modification. The SEM images showed that the surface of AMMB had a more regular and clearer structure with fewer impurities. The improvement of surface properties of AMMB significantly increased its adsorbing capacity of tetracycline in the soil. The adsorption kinetics of tetracycline by AMMB were better fitted by the pseudo‐second‐order kinetic model, suggesting that the adsorption of tetracycline on biochar followed the process of chemisorption. The adsorption mechanisms mainly involved the pore filling, hydrophobic effect, and π–π EDA interaction. Moreover, after a 60 days amendment of AMMB, the total relative abundances (RAs) of tested tetracycline resistance genes (TRGs) in soil decreased significantly, which suggested that AMMB can be a potential material to reduce risks of antibiotics and its resistance genes.

Key taxa and mobilome-mediated responses co-reshape the soil antibiotic resistome under dazomet fumigation stress

Agrochemicals are emergingly being implicated in the widespread dissemination of antibiotic resistance genes (ARGs) in agroecosystems. However, minimal research exists on the disturbance of fumigant on soil ARGs. Focusing on a typical fumigant dazomet in a simulated soil microcosm, we characterized the dazomet-triggered timely response and longstanding dynamic of ARGs at one-fold and two-fold field recommended doses using metagenome and quantitative PCR. Dazomet treatments reduced 13.17%-69.98% of absolute abundance of 16S rRNA gene and targeted ARGs, but, awfully, boosted diversity and relative abundance of ARGs up to 1.33–1.60 and 1.62–1.90 folds, respectively. Approximately 77.28% of changes in relative abundance of ARGs could be explained by bacterial community and mobile genetic elements (MGEs). Mechanistically, primary hosts of ARGs shifted from Proteobacteria (control) to Firmicutes and Actinobacteria (treatments) accompanied with corresponding changes in their abundance by combining community analysis, host tracking analysis and antibiotic resistant bacteria assay. Meanwhile, dazomet exposure significantly increased the incidence of MGEs and stimulated the conjugation of antibiotic-resistant plasmid. In addition, absolute abundance of targeted ARGs gradually recovered in the post-fumigation stage. Collectively, our results elucidate the dazomet-triggered emergence and spread of soil ARGs and highlight the importance of navigating toward rational use of fumigant in agricultural fields.

The effect of bulk-biochar and nano-biochar amendment on the removal of antibiotic resistance genes in microplastic contaminated soil

Biochar amendment has significant benefits in removing antibiotic resistance genes (ARGs) in the soil. Nevertheless, there is little information on ARGs removal in microplastic contaminated soil. Herein, a 42-day soil microcosm experiment were carried out to study how two coconut shell biochars (bulk- and nano-size) eliminate soil ARGs with/without microplastic presence. The results showed that microplastic increased significantly the numbers and abundances of ARGs in soil at 14d of cultivation. And, two biochars amendment effectively inhibited soil ARGs spread whether or not microplastic was present, especially for nano-biochar which had more effective removal compared to bulk-biochar. However, microplastic weakened soil ARGs removal after applying same biochar. Two biochars removed ARGs through decreasing horizontal gene transfer (HGT) of ARGs, potential host-bacteria abundances, some bacteria crowding the eco-niche of hosts and promoting soil properties. The adverse effect of microplastic on ARGs removal was mainly caused by weakening mobile genetic elements (MGEs) removal, and by changing soil properties. Structural equation modeling (SEM) analysis indicated that biochar's effect on ARGs profile was changed by its size and microplastic presence through altering MGEs abundances. These results highlight that biochar amendment is still an effective method for ARGs removal in microplastic contaminated soil.