The effect of ultralow-dose antibiotics exposure on soil nitrate and N2O flux

Effects of sulfamethazine on microbially-mediated denitrifying anaerobic methane oxidation in estuarine wetlands

Nitrite/nitrate-dependent anaerobic methane oxidation (n-DAMO) is an important methane (CH4) consumption and nitrogen (N) removal pathway in estuarine and coastal wetlands. Antibiotic contamination is known to affect microbially mediated processes; however, its influences on n-DAMO and the underlying molecular mechanisms remain poorly understood. In the present study, using 13CH4 tracer method combined with molecular techniques, we investigated the responses of n-DAMO microbial abundance, activity, and the associated microbial community composition to sulfamethazine (SMT, a sulfonamide antibiotic, with exposure concentrations of 0.05, 0.5, 5, 20, 50, and 100 µg L-1). Results showed that the effect of SMT exposure on n-DAMO activity was dose-dependent. Exposure to SMT at concentrations of up to 5 µg L-1 inhibited the potential n-DAMO rates (the average rates of nitrite- and nitrate-DAMO decreased by 92.9 % and 79.2 % relative to the control, respectively). In contrast, n-DAMO rates tended to be promoted by SMT when its concentration increased to 20-100 µg L-1 (the average rates of nitrite- and nitrate-DAMO increased by 724.1 % and 630.1 % relative to the low-doses, respectively). Notably, low-doses of SMT suppressed nitrite-DAMO to a greater extent than nitrate-DAMO, indicating that nitrite-DAMO was more sensitive to SMT than nitrate-DAMO. Molecular analyses suggest that the increased n-DAMO activity under high-doses SMT exposure may be driven by changes in microbial communities, especially because of the promotion of methanogens that provide more CH4 to n-DAMO microbes. Moreover, the abundances of n-DAMO microbes at high SMT exposure (20 and 50 µg L-1) were significantly higher than that at low SMT exposure (0.05-5 µg L-1). These results advance our understanding of the ecological effects of SMT on carbon (C) and N interactions in estuarine and coastal wetlands.

Effects of antibiotics on microbial nitrogen cycling and N2O emissions: A review

Sulfonamides, quinolones, tetracyclines, and macrolides are the most prevalent classes of antibiotics used in both medical treatment and agriculture. The misuse of antibiotics leads to their extensive dissemination in the environment. These antibiotics can modify the structure and functionality of microbial communities, consequently impacting microbial-mediated nitrogen cycling processes including nitrification, denitrification, and anammox. They can change the relative abundance of nirK/norB contributing to the emission of nitrous oxide, a potent greenhouse gas. This review provides a comprehensive examination of the presence of these four antibiotic classes across different environmental matrices and synthesizes current knowledge of their effects on the nitrogen cycle, including the underlying mechanisms. Such an overview is crucial for understanding the ecological impacts of antibiotics and for guiding future research directions. The presence of antibiotics in the environment varies widely, with significant differences in concentration and type across various settings. We conducted a comprehensive review of over 70 research articles that compare various aspects including processes, antibiotics, concentration ranges, microbial sources, experimental methods, and mechanisms of influence. Antibiotics can either inhibit, have no effect, or even stimulate nitrification, denitrification, and anammox, depending on the experimental conditions. The influence of antibiotics on the nitrogen cycle is characterized by dose-dependent responses, primarily inhibiting nitrification, denitrification, and anammox. This is achieved through alterations in microbial community composition and diversity, carbon source utilization, enzyme activities, electron transfer chain function, and the abundance of specific functional enzymes and antibiotic resistance genes. These alterations can lead to diminished removal of reactive nitrogen and heightened nitrous oxide emissions, potentially exacerbating the greenhouse effect and related environmental issues. Future research should consider diverse reaction mechanisms and expand the scope to investigate the combined effects of multiple antibiotics, as well as their interactions with heavy metals and other chemicals or organisms.

Influence of Four Veterinary Antibiotics on Constructed Treatment Wetland Nitrogen Transformation

The use of wetlands as a treatment approach for nitrogen in runoff is a common practice in agroecosystems. However, nitrate is not the sole constituent present in agricultural runoff and other biologically active contaminants have the potential to affect nitrate removal efficiency. In this study, the impacts of the combined effects of four common veterinary antibiotics (chlortetracycline, sulfamethazine, lincomycin, monensin) on nitrate-N treatment efficiency in saturated sediments and wetlands were evaluated in a coupled microcosm/mesocosm scale experiment. Veterinary antibiotics were hypothesized to significantly impact nitrogen speciation (e.g., nitrate and ammonium) and nitrogen uptake and transformation processes (e.g., plant uptake and denitrification) within the wetland ecosystems. To test this hypothesis, the coupled study had three objectives: 1. assess veterinary antibiotic impact on nitrogen cycle processes in wetland sediments using microcosm incubations, 2. measure nitrate-N reduction in water of floating treatment wetland systems over time following the introduction of veterinary antibiotic residues, and 3. identify the fate of veterinary antibiotics in floating treatment wetlands using mesocosms. Microcosms containing added mixtures of the veterinary antibiotics had little to no effect at lower concentrations but stimulated denitrification potential rates at higher concentrations. Based on observed changes in the nitrogen loss in the microcosm experiments, floating treatment wetland mesocosms were enriched with 1000 μg L-1 of the antibiotic mixture. Rates of nitrate-N loss observed in mesocosms with the veterinary antibiotic enrichment were consistent with the microcosm experiments in that denitrification was not inhibited, even at the high dosage. In the mesocosm experiments, average nitrate-N removal rates were not found to be impacted by the veterinary antibiotics. Further, veterinary antibiotics were primarily found in the roots of the floating treatment wetland biomass, accumulating approximately 190 mg m-2 of the antibiotic mixture. These findings provide new insight into the impact that veterinary antibiotic mixtures may have on nutrient management strategies for large-scale agricultural operations and the potential for veterinary antibiotic removal in these wetlands.

The greenhouse effect of antibiotics: The influence pathways of antibiotics on methane release from freshwater sediment

The impact of antibiotics on methane (CH₄) release from sediment involves both CH₄ production and consumption processes. However, most relevant studies lack a discussion of the pathways by which antibiotics affect CH₄ release and do not highlight the role played by the sediment chemical environment in this influence mechanism. Here, we collected field surface sediments and grouped them with various antibiotic combination concentration gradients (50, 100, 500, 1000 ng g^-1) under a 35-day indoor anaerobic constant temperature incubation. We found that the positive effect of antibiotics on sediment CH₄ release potential appeared later than the positive effect on sediment CH₄ release flux. Still, the positive effect of high-concentration antibiotics (500, 1000 ng g^-1) occurred with a lag in both processes. Also, the positive effect of high-concentration antibiotics was significantly higher than low-concentration antibiotics (50, 100 ng g^-1) in the later incubation period (p < 0.05). We performed a multi-collinearity assessment of sediment biochemical indicators, followed by a generalized linear model with negative binomial regression (GLM-NB) to obtain essential variables. In particular, we conducted the interaction analysis on CH₄ release potential and flux regression for the influence pathways construction. The partial least-squares path modeling (PLS-PM) demonstrated that the positive effect of antibiotics on CH₄ release (Total effect = 0.2579) was primarily attributed to their effect on the sediment chemical environment (Direct effect = 0.5107). These findings greatly expand our understanding of the antibiotic greenhouse effect in freshwater sediment. Further studies should more carefully consider the effects of antibiotics on the sediment chemical environment, and continuously improve the mechanistic studies of antibiotics on sediment CH₄ release.

Differential response of N2O emissions, N2O-producing and N2O-reducing bacteria to varying tetracycline doses in fertilized soil

Tetracyclines are the most widely used antibiotics worldwide. Their presence in soils could affect nutrient cycling, but our knowledge regarding how they affect soil microbial communities involved in greenhouse gas emissions is limited. The objective of the current study was to evaluate how tetracycline is affecting N₂O emissions and the abundance of denitrifiers in fertilized soil. For this purpose, soil mesocosms were treated with only NH₄NO₃ (100 mg/kg) or NH₄NO₃ (100 mg/kg) plus three different doses of tetracycline (0.1, 0.5 and 2 mg/kg). Soils that did not receive tetracycline or NH₄NO₃ were used as controls. Nitrous oxide fluxes were monitored daily for 16 days. The total bacterial (16S rRNA), the abundance of N₂O-reducing and -producing bacteria were quantified by qPCR at the end of the experiment. The application of NH₄NO₃ caused a significant increase of N₂O emissions and AOB abundance but did not affect the abundance of denitrifiers and AOA compared to control soils. Different doses of tetracycline in fertilized soils did not mitigate these N₂O emissions; instead, higher cumulative emissions were noticed in soils treated with the lowest dose. In these soils the total bacterial abundance was higher compared to soils received higher tetracycline concentration. The abundances of the N₂O-producing and N₂O-reducing communities were also differently affected by the addition of tetracycline, which was dose-dependent. Higher doses of tetracycline favored N₂O-reducers within the total bacterial community, which could be important for mitigating N₂O emissions in the long term.

Insight into co-hosts of nitrate reduction genes and antibiotic resistance genes in an urban river of the qinghai-tibet plateau

Microbial co-hosts of nitrate reduction genes (NRGs) and antibiotic resistance genes (ARGs) have been recently reported, but their ecology and biochemical role in urban waterways remain largely unknown. Here, we collected 29 surface water and 29 sediment samples in the Huangshui River on the Qinghai-Tibet Plateau during the wet and dry season, and 11 water samples from wastewater treatment plants and wetlands along the river. Using metagenomic sequencing, we retrieved 278 medium-to-high-quality metagenome-assembled genomes (MAGs) of NRG-ARG co-hosts, mainly belonging to the phyla Proteobacteria, Actinobacteriota, and Bacteroidota. Of microorganisms carrying ARGs, a high proportion (75.3%‒94.9%) also encoded NRGs, supporting nitrate reducing bacteria as dominant hosts of ARGs. Seasonal changes in antibiotic levels corresponded to significant variation in the relative abundance of NRG-ARG co-host in both water and sediments, resulting in a concomitant change in antibiotic resistance pathways. In contrast, the contribution of NRG-ARG co-hosts to nitrate reduction was stable between seasons. We identify specific antibiotics (e.g., sulphonamides) and microbial taxa (e.g., Acinetobacter and Hafnia) that may disproportionately impact these relationships to serve as a basis for laboratory investigations into bioremediation strategies. Our study suggests that highly abundant nitrate reducing microorganisms in contaminated environments may also directly impact human health as carriers of antibiotic resistance.

Impact of eight widely consumed antibiotics on the growth and physiological profile of natural soil microbial communities

Antibiotics' (ATBs) occurrence in soil ecosystems has a relevant effect in the structure and functionality of edaphic microbial communities, mainly because of their amendment with manure and biosolids that alter their key ecological functions. In this study, the impact of eight widely consumed ATBs on a natural soil microbial community, characterized through 16 S rRNA gene sequencing, was evaluated. Changes induced by the ATBs in the growth of the soil microbiota and in the community-level physiological profiling (CLPP), using Biolog EcoPlates™, were measured as endpoint. The eight assayed ATBs lead to a significant decrease in the growth of soil microbial communities in a dose-dependent way, ordered by its effect as follows: chloramphenicol > gentamycin > erythromycin > ampicillin > penicillin > amoxicillin > tetracycline > streptomycin. Chloramphenicol, gentamycin, and erythromycin adversely affected the physiological profile of the soil community, especially its ability to metabolize amino acids, carboxylic and ketonic acids and polymers. The analysis of the relationship between the physico-chemical properties of ATBs, as well as their mechanism of action, revealed that, except for the aminoglycosides, each ATB is influenced by a different physico-chemical parameters, even for ATBs of the same family. Significant effects were detected from 100 μg mL to 1, concentrations that can be found in digested sludge, biosolids and even in fertilized soils after repeated application of manure, so cumulative and long-term effects of these antibiotics on soil environment cannot be ruled out.

Antibiotics sulfamethoxazole alter nitrous oxide production and pathways in estuarine sediments: Evidenced by the N15-O18 isotopes tracing

Estuarine antibiotic residues are profoundly impacting microbial nitrogen (N) cycling and associated N₂O production, but the response of N₂O production pathways to antibiotics remains poorly understood. Here, ¹⁵N-¹⁸O labeling technique combined with molecular methods were used to investigate the impacts of sulfamethoxazole on the contribution of ammonia oxidation (nitrifier nitrification, nitrifier denitrification, and nitrification-coupled denitrification) and heterotrophic denitrification (HD) to N₂O production in estuarine sediments. Results showed that environmental concentration of sulfamethoxazole (4 ng/g) promoted the total N₂O production by 17.1% through nitrifier denitrification. Environmentally relevant (40-4000 ng/g) and irrelevant (40,000 ng/g) concentration of sulfamethoxazole drove nitrification denitrification to gradually lose the dominant role in total N₂O production and ammonia oxidation-derived N₂O, replaced by HD and nitrifier nitrification, while total N₂O production were inhibited. Furthermore, when HD dominated the total N₂O production, the HD-derived N₂O increased by 63.6% with sulfamethoxazole concentration reaching 40,000 ng/g. The mechanistic investigation further showed that nitrifying bacteria were more susceptible to sulfamethoxazole than nitrifying archaea and denitrifiers. The increased expression of nirS gene carried by non-dominant denitrifiers improved the ratio of nirS:nosZ and hence increased HD-derived N₂O under high sulfamethoxazole stresses. Overall, our results provide a comprehensive view into how antibiotics regulate N₂O production and its pathways in estuarine sediments.

Effects of pharmaceuticals on the nitrogen cycle in water and soil: a review

The effects of pharmaceuticals on the nitrogen cycle in water and soil have recently become an increasingly important issue for environmental research. However, a few studies have investigated the direct effects of pharmaceuticals on the nitrogen cycle in water and soil. Pharmaceuticals can contribute to inhibition and stimulation of nitrogen cycle processes in the environment. Some pharmaceuticals have no observable effect on the nitrogen cycle in water and soil while others appeared to inhibit or stimulate for it. This review reports on the most recent evidence of effects of pharmaceuticals on the nitrogen cycle processes by examination of the potential impact of pharmaceuticals on nitrogen fixation, nitrification, ammonification, denitrification, and anammox. Research studies have identified pharmaceuticals that can either inhibit or stimulate nitrification, ammonification, denitrification, and anammox. Among these, amoxicillin, chlortetracycline, ciprofloxacin, clarithromycin, enrofloxacin, erythromycin, narasin, norfloxacin, and sulfamethazine had the most significant effects on nitrogen cycle processes. This review also clearly demonstrates that some nitrogen transformation processes such as nitrification show much higher sensitivity to the presence of pharmaceuticals than other nitrogen transformations or flows such as mineralization or ammonia volatilization. We conclude by suggesting that future studies take a more comprehensive approach to report on pharmaceuticals' impact on the nitrogen cycle process.

Environmental heterogeneity determines the response patterns of microbially mediated N-reduction processes to sulfamethoxazole in river sediments

The widespread occurrence of antibiotics in aquatic ecosystems leads to potential ecological risks to organisms, in turn affecting microbially mediated processes. Here, we investigated the response of dominant N-reduction processes to the frequently detected antibiotic sulfamethoxazole (SMX) along the Chaobai River with regional environmental heterogeneity, including denitrification, anaerobic ammonium oxidation (anammox), dissimilatory nitrate reduction to ammonium (DNRA), and nitrous oxide (N₂O) release. We found two divergent SMX response patterns for denitrification in contrasting scenarios of geochemical properties. In the context of low nitrate and carbon, SMX weakened denitrification with a slightly stimulation first. Whereas SMX directly inhibited denitrification when nitrate and carbon were sufficient. High SMX concentration suppressed anammox (26-72%) and DNRA activities (48-84%) via restraining the activities of anammox and DNRA bacteria. Notably, SMX increased the contribution of denitrification to N-reduction at the expense of DNRA to N-reduction, leading to a shift in nitrogen conversion towards denitrification. Additionally, SMX stimulated N₂O emission (up to 91%) due to superior restraint on process of N₂O reduction to N₂ and an incline for N-reduction towards denitrification, thereby exacerbating greenhouse effect. Our results advance the understanding of how nitrogen cycling is affected by SMX in aquatic ecosystems with environmental heterogeneity.

Sulfamethoxazole biodegradation and impacts on soil microbial communities in a Bolivian arid high altitude catchment

The processes controlling antibiotics fate in ecosystems are poorly understood, yet their presence can inhibit bacterial growth and induce the development of bacterial resistance. Sulfamethoxazole (SMX) is one of the most frequently detected sulfonamides in natural environments due to its low metabolism and molecular properties. This work presents pioneering results on SMX biodegradation and impact in high altitude soils (Bolivian Altiplano), allowing a better understanding of the persistence, spread and impact of this antibiotic at the global watershed scale. Our results showed significant dissipation of SMX in relation to its adsorption, hydrolysis and biotransformation. However, biodegradation appears to be lower in these mountain soils than in lowland soils as widely described in the literature. The half-life of SMX ranges from 12 to 346 days in non-sterile soils. In one soil, no biotic degradation was observed, indicating a likely high persistence. Biodegradation was related to OC content and to proximity to urban activities. Regarding the study of the impacts of SMX, the DGGE results were less sensitive than the sequencing. In general, SMX strongly changes the structure and composition of the studied soils at high altitudes, which is comparable to the observations of other authors in lowland soils. The phylum Actinobacter showed high sensitivity to SMX. In contrast, the abundance of ɣ-proteobacteria remained almost unchanged. Soil contamination with SMX did not lead to the development of the studied resistance genes (sul1 and sul2) in soils where they were absent at the beginning of the experiment. Thus, the presence of SMX resistance genes seems to be related to irrigation with wastewater carrying the studied resistance genes.

Effects of sulfamethoxazole on nitrogen removal and molecular ecological network in integrated vertical-flow constructed wetland

Response of nitrogen removal efficiency and microbial interactions to organic pollution has been a major issue in wastewater treatment system. However, the nitrogen removal efficiency and interactions among microbial community under antibiotics press is still unclear. Thus, the effect of sulfamethoxazole (SMX) on nitrogen removal and microbial responses of IVCWs was investigated through recorded the nitrogen removal efficiency before and after adding SMX and random matrix theory (RMT)-based network analysis. Results showed that better NH₄⁺-N removal (>90%) after a long period of operation were achieved in IVCWs, but NO₃^--N was accumulated. However, nitrate removal rates were significantly increased after long-term exposure (60 d) to 100 μgL^-1 SMX (from 27.35% to 35.57%) with relatively high SMX removal (53.50%). Surprisingly, the ammonia nitrogen removal rate (90.07-92.70%) were not significantly affected by SMX in IVCWs. Moreover, the bacterial richness was decreased and the bacterial community structures were altered by the presence of SMX, especially those of nitrogen-transforming microorganisms. Molecular ecological network analysis suggested that SMX had positive influences on denitrifying bacteria interactions but reduced the network complexity and microbial interactions on whole molecular network, and among-module connections were weakened obviously at SMX.

Impact of antibiotic concentration gradients on nitrate reduction and antibiotic resistance in a microfluidic gradient chamber

In order to explore the impact of antibiotics on the bacterial metabolic cycling of nitrate within contaminated soil and groundwater environments, we compared the effects of polymyxin B (PMB) and ciprofloxacin (CIP) concentration gradients on the distribution and activity of a wild type (WT) and a flagella deficient mutant (Δflag) of Shewanella oneidensis MR-1 in a microfluidic gradient chamber (MGC). Complementary batch experiments were performed to measure bacteriostatic versus bactericidal concentrations of the two antibiotics, as well as their effect on nitrate reduction. Prior work demonstrated that PMB disrupts cell membranes while CIP inhibits DNA synthesis. Consistent with these modes of action, batch results from this work show that PMB is bactericidal at lower concentrations than CIP relative to their respective minimum inhibitory concentrations (MICs) (≥5× MIC_PMB vs. ≥20× MIC_CIP). Concentration gradients from 0 to 50× the MIC of both antibiotics were established in the MGC across a 2-cm interconnected pore network, with nutrients injected at both concentration boundaries. The WT cells could only access and reduce nitrate in regions of the MGC with PMB at <18× MIC_PMB, whereas this occurred with CIP up to 50× MIC_CIP; and cells extracted from these MGCs showed no antibiotic resistance. The distribution of Δflag cells was further limited to lower antibiotic concentrations (≤1× MIC_PMB, ≤43× MIC_CIP) due to inability of movement. These results indicate that S. oneidensis access and reduce nitrate in bactericidal regions via chemotactic migration without development of antibiotic resistance, and that this migration is inhibited by acutely lethal bactericidal levels of antibiotics.

Effects of norfloxacin on nitrate reduction and dynamic denitrifying enzymes activities in groundwater

The impact of antibiotics on denitrification has attracted widespread attention recently. Norfloxacin, as a representative of fluoroquinolone antibiotics, is extensively detected in groundwater. However, whether the release of norfloxacin into the groundwater poses potential risks to denitrification remains unclear. In this study, effect of norfloxacin on denitrification was investigated. The results showed that increasing norfloxacin from 0 to 100 μg/L decreased nitrate removal rate from 0.68 to 0.44 mg/L/h, but enhanced N2O emission by 177 folds. Additionally, 100 μg/L of norfloxacin decreased nitrite accumulation by 50.6%. Corresponding inhibition of norfloxacin on bacterial growth, carbon source utilization, electron transport system activity and genes expression was revealed. Furthermore, denitrifying enzyme dynamic monitoring results showed that norfloxacin inhibited nitrate reductase activity, and enhanced nitrite reductase activity to some extent in denitrification process, which was consistent with the variations of nitrate and nitrite. Meanwhile, sensitivity analysis demonstrated that nitrate reductase was more easily affected by norfloxacin than nitrite reductase. Overall, this study suggests that multiple regulation of denitrifying enzyme activity contributes to evaluating the comprehensive effects of antibiotics on groundwater denitrification.

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

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

Effect of straw-derived dissolved organic matter on the adsorption of sulfamethoxazole to purple paddy soils

The presence of sulfamethoxazole (SMX) in croplands has become an international concern. The environmental behavior and fate of SMX in agricultural soils are not well understood, especially when the adsorption behavior is disturbed by the dissolved organic matter (DOM) released by crop straw. As canola straw is one of the biomasses widely returned to farmlands, we characterized DOM derived from pristine and decomposed canola straw, and explored the effects and mechanisms of the DOMs on regulating SMX adsorption to purple paddy soils. The spectral analysis showed that the molecular weight, aromaticity, and hydrophobicity of canola straw-derived DOM increased as decomposition proceeded. These physicochemical properties collectively determined the effects of the DOM on SMX adsorption. The DOM derived from pristine canola straw increased SMX maximum adsorption capacity of the soils by approximately 2.6 times, but this positive effect gradually decreased to a steady state by day 90 in the straw decomposition period. Nevertheless, the SMX adsorption behavior in the soils was invariably determined by the DOM extracts. These adsorption processes of SMX were well fitted by the double-chamber kinetics model and the Langmuir and Freundlich thermodynamic models. Thermodynamic parameters indicated that SMX adsorption onto the soils was spontaneous and endothermic, and this adsorption characteristics was not significantly (p > 0.05) changed by the DOM extracts. However, the adsorption kinetics were altered by those DOMs, i.e., the fast and slow adsorption processes were both diminished. Correspondingly, co-adsorption and cumulative adsorption were identified as the main mechanisms determining SMX adsorption to the purple paddy soils in the presence of the straw-derived DOMs. These results collectively indicated that the DOMs released by straw in croplands may decrease the ecological risks of organic pollutants by inhibiting their migration processes.

Simultaneous aerobic denitrification and antibiotics degradation by strain Marinobacter hydrocarbonoclasticus RAD-2

Simultaneous denitrification and antibiotics (oxytetracycline, OTC and ciprofloxacin, CFX) degradation was evaluated using a typical aerobic denitrifying strain Marinobacter hydrocarbonoclasticus RAD-2. There was no significant influence on the aerobic nitrate removal efficiency of strain RAD-2 in the presence of these two antibiotics. Along with denitrification, the average degradation rate of 2.92 μg OTC L^-1h^-1 was achieved, while no degradation was observed for CFX. The growth behavior indicated that an insignificant inhibition effect could have occurred at an antibiotics dosage lower than 300 μg/L. The transcriptional results revealed that antibiotics exposure caused (<2h) down-regulation of the denitrifying related genes, but triggered a significant subsequent up-regulation (4 h). Less nitrous oxide productions were observed in both aerobic and anoxic denitrification processes with antibiotics. Overall, the hormesis effect caused by antibiotics exposure indicated a potential approach to enhance the co-metabolism degradation performance for nitrate and antibiotics in aerobic denitrification.

The simultaneous antibiotics and nitrogen removal in vertical flow constructed wetlands: Effects of substrates and responses of microbial functions

A vertical flow constructed wetland (VFCW) packed with the different substrates was designed to remediate the antibiotics in the wastewater. Zeolite (CW-Z) paralleled with Manganese (Mn) ore (CW-M) and biochar (CW-C) were used to enhance the synchronous removal of ciprofloxacin hydrochloride (CIPH), sulfamethazine (SMZ) and nitrogen (N) from the wastewater. The result indicated that CW-M had a significant potential to remove CIPH (93%), SMZ (69%), TN (71%), NH₄⁺-N (94%) and NO₃^--N (94%) across all the treatments. The abundance of amoA, nirK and nirS genes are dramatically higher in CW-M and CW-C, while CW-C inhibited the production of quinolone resistance genes. Results showed that different substrates could affect the microbial diversity and structure. The addition of Mn ore to the water led to an improved abundance of nitrogen-related phyla. Overall, Mn ore has a considerable potential to simultaneously remove antibiotics and N in VFCWs.

The effects of trace narasin on the biogeochemical N-cycle in a cultivated sandy loam

Narasin is an antibiotic administered to broiler chickens to prevent coccidiosis. After storage, excreta containing parent narasin compounds is commonly spread as nitrogen fertilizer, yielding initial soil concentrations in the low μg·kg^-1 range. In soil, antibiotics have been found to modify one or more pathways in the biogeochemical nitrogen cycle. The concentrations tested are often too high to be considered environmentally relevant, despite evidence that sub-therapeutic doses may also be disruptive. We conducted soil mesocosm experiments to determine the overall impact of trace narasin on major nitrogen pools and fluxes in soils treated with 0, 1, 10, 100, or 1000 ng·kg^-1 narasin. Water content in the mesocosms varied from 40% to 80% water-filled pore space (WFPS), simulating a range of different redox conditions. Under aerobic conditions (40% WFPS), exposure to narasin inhibited nitrification, yielding increases in soil ammonium by up to 76%, perhaps by targeting nitrifying fungi. Under the same conditions, narasin caused soil nitrate concentrations to decline 17-39%. When the soil was near saturation (80% WFPS), nitrate increased by an average of 30%. Mass balances and isotopic enrichment of N₂O indicate that NAR may also affect anammox and the rate of nitrifier nitrification/denitrification. In aerobic soils, N₂O flux increased with antibiotic dose and the rise in flux strongly correlates to the N₂O:N₂ product ratio from dentification. This relationship suggests that N₂O flux may increase in soils exposed to narasin even when total denitrification is modestly inhibited. We conclude that trace concentrations of narasin can significantly modify biogeochemical activities in soil on short timescales. Our results indicate the potential for extremely low concentrations of antibiotics to impact agricultural productivity, terrestrial N₂O flux, and non-point source nitrogen pollution.

Effects of Sulfamethoxazole and 2-Ethylhexyl-4-Methoxycinnamate on the Dissimilatory Nitrate Reduction Processes and N2O Release in Sediments in the Yarlung Zangbo River

The nitrogen pollution of rivers as a global environmental problem has received great attentions in recent years. The occurrence of emerging pollutants in high-altitude rivers will inevitably affect the dissimilatory nitrate reduction processes. In this study, sediment slurry experiments combined with ¹⁵N tracer techniques were conducted to investigate the influence of pharmaceutical and personal care products (alone and in combination) on denitrification and the anaerobic ammonium oxidation (anammox) process and the resulting N₂O release in the sediments of the Yarlung Zangbo River. The results showed that the denitrification rates were inhibited by sulfamethoxazole (SMX) treatments (1-100 μg L^-1) and the anammox rates decreased as the SMX concentrations increased, which may be due to the inhibitory effect of this antibiotic on nitrate reducing microbes. 2-Ethylhexyl-4-methoxycinnamate (EHMC) impacted nitrogen transformation mainly though the inhibition of the anammox processes. SMX and EHMC showed a superposition effect on the denitrification processes. The expression levels of the denitrifying functional genes nirS and nosZ were decreased and N₂O release was stimulated due to the presence of SMX and/or EHMC in the sediments. To the best of our knowledge, this study is the first to report the effects of EHMC and its mixtures on the dissimilatory nitrate reduction processes and N₂O releases in river sediments. Our results indicated that the widespread occurrence of emerging pollutants in high-altitude rivers may disturb the nitrogen transformation processes and increase the pressure of global warming.

A global environmental health perspective and optimisation of stress

The phrase "what doesn't kill us makes us stronger" suggests the possibility that living systems have evolved a spectrum of adaptive mechanisms resulting in a biological stress response strategy that enhances resilience in a targeted quantifiable manner for amplitude and duration. If so, what are its evolutionary foundations and impact on biological diversity? Substantial research demonstrates that numerous agents enhance biological performance and resilience at low doses in a manner described by the hormetic dose response, being inhibitory and/or harmful at higher doses. This Review assesses how environmental changes impact the spectrum and intensity of biological stresses, how they affect health, and how such knowledge may improve strategies in confronting global environmental change.

Effects of triclosan and triclocarban on denitrification and N2O emissions in paddy soil

Triclosan (TCS) and triclocarban (TCC) are two common antimicrobial compounds, which are widely used as ingredients in pharmaceuticals and personal care products. They occur ubiquitously in soil due to biosolid application as agricultural fertilizers, but their influence on microbially mediated soil biogeochemical processes is poorly understood. We tested the effects of varying concentrations of TCS and TCC applied both individually and together on denitrification and N₂O emissions in paddy soil. We also quantified denitrification functional gene abundances by q-PCR to elucidate the microbial mechanisms of TCS and TCC's effects. Our results showed that TCS and TCC exposure both individually and together significantly (p < 0.05) inhibited denitrification (7.0-36.7%) and N₂O emissions (15.4-86.4%) except for the 0.01 mg kg^-1 TCC treatment in which denitrification was slightly but significantly (p < 0.05) stimulated. The inhibitory effects of TCS and TCC exposure were mainly attributed to their negative net effects on denitrifying bacteria as suggested by the decrease in abundances of 16S rRNA, narG, nirK and clade I nosZ genes in the TCS and TCC treatments. Overall, we found that TCS and TCC exposure in paddy soil could substantially alter nitrogen cycling in rice paddy ecosystems by inhibiting denitrification and N₂O emissions. These effects should be taken into consideration when evaluating the environmental impacts of TCS and TCC.

Fate and behaviour of veterinary sulphonamides under denitrifying conditions

Antibiotics are among the most widely administered drugs in the growing animal food industry. Of all the antibiotics approved for agriculture, sulphonamides are of particular interest. Their spectrum of activity is broad, affecting gram-positive, gram-negative, and many protozoal organisms, and they have been used for the treatment of a wide variety of animals. Animal manure is one of primary sources of soil contamination by sulphonamides. As they have a low soil sorption potential and are therefore highly mobile in soil, they can be transported to groundwater. In the present study, papers dealing with the fate and behaviour of veterinary sulphonamides under denitrifying conditions often arising in the subsurface are reviewed. Veterinary sulphonamide-exposed conditions can result in either inhibition or stimulation of the denitrification process owing to their toxicity or stress for denitrifiers. The effect of sulphonamides on individual denitrification steps is unbalanced, which can cause accumulation of process intermediates (dinitrogen oxide, nitrites). Although research results related to veterinary sulphonamide biodegradation in a nitratereducing environment show great variety, they indicate that these compounds are biodegradable under denitrifying conditions, that their biodegradation fits the first-order kinetics model, and that microbial action is the main mechanism of their dissipation. Regarding biodegradation pathways, research to date has only focused on sulfamethoxazole. Its degradation is driven by the presence of nitrous acid, which is formed from nitrites generated by the denitrification process as an intermediate product. Nevertheless, sulfamethoxazole degradation is abiotic, meaning that it does not participate in the denitrifying metabolism. For the formation of sulfamethoxazole transformation products, including its nitro, nitroso and desamino derivatives, the presence of the primary aromatic amine group is key. As this functional group is common for all sulphonamides, it can be assumed that these transformation products are also involved in the degradation pathways of other sulphonamides.

Analysis for microbial denitrification and antibiotic resistance during anaerobic digestion of cattle manure containing antibiotic

This study investigated the effects of tylosin (0, 10, and 100 mg/kg dry weight) on the denitrification genes and microbial community during the anaerobic digestion of cattle manure. N₂ emissions were reduced and N₂O emissions were increased by 10 mg/kg tylosin. Adding 100 mg/kg tylosin increased the emission of both N₂O and N₂. The different responses of denitrifying bacteria and genes to tylosin may have been due to the presence of antibiotic resistance genes (ARGs). Network analysis indicated that denitrification genes and ARGs had the same potential host bacteria. intI1 was more important for the horizontal transfer of denitrification genes and ARGs during anaerobic digestion than intI2. The anaerobic digestion of manure containing tylosin may increase nitrogen losses and the associated ecological risk.

Assessing the risk of utilizing tidal coastal wetlands for wastewater management

Coastal tidal wetlands are well recognized for the key ecosystem services they provide such as flood protection, water quality improvement, and carbon sequestration. In the southeastern United States, some communities rely on coastal wetlands for the management of secondarily treated effluents in forested and emergent wetlands. Advocates for this practice have argued that wetlands can assimilate nitrogen from wastewater, which can improve cypress-tupelo swamp productivity, and enhance marsh accretion rates to mitigate the effects of sea level rise. In contrast, evolving research on coastal wetlands and the environmental impacts of wastewater treatment pose new questions about the potential risks introduced by this practice. This review seeks to: (1) assess current research on plant productivity in fertilized coastal wetlands; (2) highlight the occurrence and fate of pharmaceuticals and personal care products (PPCPs) in municipal wastewater operations; and (3) identify knowledge gaps. Nutrient additions via wastewater augmented aboveground productivity, but decreased belowground productivity and root-to-shoot ratios. Removal efficiencies of some PPCPs by coastal wetlands have been substantial (75% - 99%), but most remain unevaluated. Furthermore, their fate and effect on local ecosystem function and biogeochemical processes remain in question. This review demonstrates that there is more research needed at both local and watershed scales to evaluate how these risk factors impact ecosystem integrity and to better understand the tradeoffs with this wastewater management practice.

Effects of ofloxacin on nitrogen removal and microbial community structure in constructed wetland

Constructed wetlands (CWs) have emerged as a promising technology for the purification of micro-polluted water. However, their nitrogen removal performance can be significantly degraded by design, operational, and environmental factors. The present study investigates the effects of ofloxacin (OFL: 0.1, 10, and 1000 μg L^-1) and plants (Cyperus alternifolius L. and Typha angustifolia L.) on nitrogen removal in a micro-polluted CW system over a duration of 12 weeks. The effects were evaluated by investigating NH₄-N and NO₃-N removal efficiency, nitrification genes (amoA-AOA and amoA-AOB), denitrification genes (nirK and nirS), fungal 18S rRNA gene and microorganism community structure. The results showed that in unplanted CWs, OFL increased the NH₄-N removal efficiency (from 72.6% to 80.7-82.1%), the abundances of amoA-AOA, nirS, nirK and fungal 18S rRNA gene, and the bacterial diversity but decreased the abundance of both amoA-AOB and bacterial richness. In contrast, both the nitrogen removal efficiency (83.4-89.5% for NH₄-N and 33.8-38.5% for NO₃-N) and bacterial diversity/richness were not significantly affected by OFL in planted CWs. In planted systems, OFL increased the relative abundance of Arthrobacter, Pseudomonas, and Enterococcus, which are proven antibiotic-resistant bacteria. This study showed that CWs are able to remove nitrogen from antibiotic-contaminated micro-polluted water, which might primarily be attributed to the presence of plants that protect the microorganism community.

Antibiotics in the Soil Environment-Degradation and Their Impact on Microbial Activity and Diversity

Antibiotics play a key role in the management of infectious diseases in humans, animals, livestock, and aquacultures all over the world. The release of increasing amount of antibiotics into waters and soils creates a potential threat to all microorganisms in these environments. This review addresses issues related to the fate and degradation of antibiotics in soils and the impact of antibiotics on the structural, genetic and functional diversity of microbial communities. Due to the emergence of bacterial resistance to antibiotics, which is considered a worldwide public health problem, the abundance and diversity of antibiotic resistance genes (ARGs) in soils are also discussed. When antibiotic residues enter the soil, the main processes determining their persistence are sorption to organic particles and degradation/transformation. The wide range of DT50 values for antibiotic residues in soils shows that the processes governing persistence depend on a number of different factors, e.g., physico-chemical properties of the residue, characteristics of the soil, and climatic factors (temperature, rainfall, and humidity). The results presented in this review show that antibiotics affect soil microorganisms by changing their enzyme activity and ability to metabolize different carbon sources, as well as by altering the overall microbial biomass and the relative abundance of different groups (i.e., Gram-negative bacteria, Gram-positive bacteria, and fungi) in microbial communities. Studies using methods based on analyses of nucleic acids prove that antibiotics alter the biodiversity of microbial communities and the presence of many types of ARGs in soil are affected by agricultural and human activities. It is worth emphasizing that studies on ARGs in soil have resulted in the discovery of new genes and enzymes responsible for bacterial resistance to antibiotics. However, many ambiguous results indicate that precise estimation of the impact of antibiotics on the activity and diversity of soil microbial communities is a great challenge.

Environmental fate and microbial effects of monensin, lincomycin, and sulfamethazine residues in soil

The impact of commonly-used livestock antibiotics on soil nitrogen transformations under varying redox conditions is largely unknown. Soil column incubations were conducted using three livestock antibiotics (monensin, lincomycin and sulfamethazine) to better understand the fate of the antibiotics, their effect on nitrogen transformation, and their impact on soil microbial communities under aerobic, anoxic, and denitrifying conditions. While monensin was not recovered in the effluent, lincomycin and sulfamethazine concentrations decreased slightly during transport through the columns. Sorption, and to a limited extent degradation, are likely to be the primary processes leading to antibiotic attenuation during leaching. Antibiotics also affected microbial respiration and clearly impacted nitrogen transformation. The occurrence of the three antibiotics as a mixture, as well as the occurrence of lincomycin alone affected, by inhibiting any nitrite reduction, the denitrification process. Discontinuing antibiotics additions restored microbial denitrification. Metagenomic analysis indicated that Proteobacteria, Bacteroidetes, Actinobacteria, and Chloroflexi were the predominant phyla observed throughout the study. Results suggested that episodic occurrence of antibiotics led to a temporal change in microbial community composition in the upper portion of the columns while only transient changes occurred in the lower portion. Thus, the occurrence of high concentrations of veterinary antibiotic residues could impact nitrogen cycling in soils receiving wastewater runoff or manure applications with potential longer-term microbial community changes possible at higher antibiotic concentrations.

Tetracycline and sulfamethazine alter dissimilatory nitrate reduction processes and increase N2O release in rice fields

Effects of antibiotics on the transformation of nitrate and the associated N₂O release in paddy fields are obscure. Using soil slurry experiments combined with ¹⁵N tracer techniques, the influence of tetracycline and sulfamethazine (applied alone and in combination) on the denitrification, anaerobic ammonium oxidation (anammox), dissimilatory nitrate reduction to ammonium (DNRA) and N₂O release rates in the paddy soil were investigated, while genes related to nitrate reduction and antibiotic resistance were quantified to explore the microbial mechanisms behind the antibiotics' effects. The potential rates of denitrification, anammox, and DNRA were significantly (p < 0.05) reduced, which were mainly attributed to the inhibitory effects of the antibiotics on nitrate-reducing microbes. However, the N₂O release rates were significantly (p < 0.05) stimulated by the antibiotic treatments (0.6-6000 μg kg^-1 soil dry weight), which were caused by the different inhibition effects of antibiotics on N₂O production and N₂O reduction as suggest by the changes in abundance of nirS (nitrite reduction step) and nosZ (N₂O reduction to N₂ step) genes. Antibiotic resistance gene (tetA, tetG, sulI, and sulIII) abundances were significantly (p < 0.05) increased under high antibiotic exposure concentrations (>600 μg kg^-1 soil dry weight). Our results suggest that the widespread occurrence of antibiotics in paddy soils may pose significant eco-environmental risks (nitrate accumulation and greenhouse effects) by altering nitrate transformation processes.

Antibiotic Effects on Microbial Communities Responsible for Denitrification and N2O Production in Grassland Soils

Antibiotics in soils may affect the structure and function of microbial communities. In this study, we investigated the acute effects of tetracycline on soil microbial community composition and production of nitrous oxide (N₂O) and dinitrogen (N₂) as the end-products of denitrification. Grassland soils were pre-incubated with and without tetracycline for 1-week prior to measurements of N₂O and N₂ production in soil slurries along with the analysis of prokaryotic and fungal communities by quantitative polymerase chain reaction (qPCR) and next-generation sequencing. Abundance and taxonomic composition of bacteria carrying two genotypes of N₂O reductase genes (nosZ-I and nosZ-II) were evaluated through qPCR and metabolic inference. Soil samples treated with tetracycline generated 12 times more N₂O, but N₂ production was reduced by 84% compared to the control. In parallel with greater N₂O production, we observed an increase in the fungi:bacteria ratio and a significant decrease in the abundance of nosZ-II carrying bacteria; nosZ-I abundance was not affected. NosZ-II-carrying Bacillus spp. (Firmicutes) and Anaeromyxobacter spp. (Deltaproteobacteria) were particularly susceptible to tetracycline and may serve as a crucial N₂O sink in grassland soils. Our study indicates that the introduction of antibiotics to agroecosystems may promote higher N₂O production due to the inhibitory effects on nosZ-II-carrying communities.

Effects of long-term pig manure application on antibiotics, abundance of antibiotic resistance genes (ARGs), anammox and denitrification rates in paddy soils

Previous studies of long-term manure applications in paddy soil mostly focused on the effects on denitrification, occurrence of antibiotics and antibiotic resistance genes (ARGs) without considering the effects on anaerobic ammonium oxidation (anammox). Here, we investigated the potential rates of anammox and denitrification, occurrence of antibiotics and AGRs in response to three fertilization regimes (C, no fertilizer; N, mineral fertilizer; and NM, N plus pig manure) in six long-term paddy experiment sites across China. The potential rates of anammox (0.11-3.64 nmol N g^-1 h^-1) and denitrification (1.5-29.05 nmol N g^-1 h^-1) were correlated with the abundance of anammox genes (hzsB) and denitrification functional genes (narG, nirK, nirS and nosZ), respectively. The anammox and denitrification rates were affected by soil organic carbon (SOC) and significantly (p < 0.05) increased in NM treatments relative to those in N treatments. Although pig manure application increased antibiotic concentrations and abundance of ARGs compared with N treatments, the increased antibiotics did not directly affect the anammox and denitrification rates. Our results suggested that long-term pig manure application significantly increased antibiotic concentrations, abundance of ARGs, and rates of anammox and denitrification, and that the effects of pig manure-derived antibiotics on anammox and denitrification were marginal. This is the first report that investigates the effects of long-term pig manure application on anammox in paddy soils. More attention should be paid to the potential ecological risk of increased ARGs caused by pig manure application in paddy soils.

4-nitroso-sulfamethoxazole generation in soil under denitrifying conditions: Field observations versus laboratory results

The formation of 4-nitroso-sulfamethoxazole and 4-nitro-SMX, two transformation products (TPs) of sulfamethoxazole (SMX) was investigated under batch soil slurry experiments and in a field study. Due to their low occurrence levels (ng/L) in environmental waters, a suitable analytical method based on liquid chromatography - high resolution - mass spectrometry was developed. Consequently, field observations revealed, for the first time, the occurrence of 4-nitroso-SMX in groundwater at concentrations as high as 18ng/L.Nitric oxide (NO) steady-state concentrations were determined in soil slurry experiments because this reactive specie accounted for the formation of 4-nitroso-SMX and 4-nitro-SMX. Measurements revealed that environmental SMX concentrations (0.2-2μg/L) at neutral pH induced the accumulation of nitric oxide. Under acidic conditions (pH<6), nitrous acid (HONO) was the major source of nitric oxide while under neutral/basic conditions nitric oxide release was related to the inhibition of denitrification processes. Under laboratory experiments, SMX nitration reaction appeared to be an irreversible transformation pathway, while 4-nitroso-SMX was slowly transformed over time. The occurrence of 4-nitroso-SMX conditions was therefore unexpected in the field study but could be due to its continuous input from soil and/or its relative persistence under anoxic conditions. A mechanism for 4-nitroso-SMX formation was proposed involving a nitrosative desamination pathway through a phenyl radical.

Enterosalivary nitrate metabolism and the microbiome: Intersection of microbial metabolism, nitric oxide and diet in cardiac and pulmonary vascular health

Recent insights into the bioactivation and signaling actions of inorganic, dietary nitrate and nitrite now suggest a critical role for the microbiome in the development of cardiac and pulmonary vascular diseases. Once thought to be the inert, end-products of endothelial-derived nitric oxide (NO) heme-oxidation, nitrate and nitrite are now considered major sources of exogenous NO that exhibit enhanced vasoactive signaling activity under conditions of hypoxia and stress. The bioavailability of nitrate and nitrite depend on the enzymatic reduction of nitrate to nitrite by a unique set of bacterial nitrate reductase enzymes possessed by specific bacterial populations in the mammalian mouth and gut. The pathogenesis of pulmonary hypertension (PH), obesity, hypertension and CVD are linked to defects in NO signaling, suggesting a role for commensal oral bacteria to shape the development of PH through the formation of nitrite, NO and other bioactive nitrogen oxides. Oral supplementation with inorganic nitrate or nitrate-containing foods exert pleiotropic, beneficial vascular effects in the setting of inflammation, endothelial dysfunction, ischemia-reperfusion injury and in pre-clinical models of PH, while traditional high-nitrate dietary patterns are associated with beneficial outcomes in hypertension, obesity and CVD. These observations highlight the potential of the microbiome in the development of novel nitrate- and nitrite-based therapeutics for PH, CVD and their risk factors.

Effects of multiple antibiotics exposure on denitrification process in the Yangtze Estuary sediments

Denitrification is a dominant reactive nitrogen removal pathway in most estuarine and coastal ecosystems, and plays a significant role in regulating N₂O release. Although multiple antibiotics residues are widely detected in aquatic environment, combined effects of antibiotics on denitrification remain indistinct. In this work, 5 classes of antibiotics (sulfonamides, chloramphenicols, tetracyclines, macrolides, and fluoroquinolones) were selected to conduct orthogonal experiments in order to explore their combined effects on denitrification. ¹⁵N-based denitrification and N₂O release rates were determined in the orthogonal experiments, while denitrifying functional genes were examined to illustrate the microbial mechanism of the combined antibiotics effect. Denitrification rates were inhibited by antibiotics treatments, and synergistic inhibition effect was observed for multiple antibiotics exposure. Different classes of antibiotics had different influence on N₂O release rates, but multiple antibiotics exposure mostly led to stimulatory effect. Abundances of denitrifying functional genes were inhibited by multiple antibiotics exposure due to the antimicrobial properties, and different inhibition on denitrifiers may be the major mechanism for the variations of N₂O release rates. Combined effects of antibiotics on denitrification may lead to nitrate retention and N₂O release in estuarine and coastal ecosystems, and consequently cause cascading environmental problems, such as greenhouse effects and hyper-eutrophication.

Change in microbial community in landfill refuse contaminated with antibiotics facilitates denitrification more than the increase in ARG over long-term

In this study, the addition of sulfamethazine (SMT) to landfill refuse decreased nitrogen intermediates (e.g. N₂O and NO) and dinitrogen (N₂) gas fluxes to <0.5 μg-N/kg-refuse·h^-1, while the N₂O and N₂ flux were at ~1.5 and 5.0 μg-N/kg-refuse·h^-1 respectively in samples to which oxytetracycline (OTC) had been added. The ARG (antibiotic resistance gene) levels in the refuse increased tenfold after long-term exposure to antibiotics, followed by a fourfold increase in the N₂ flux, but SMT-amended samples with the largest resistome facilitated the denitrification (the nitrogen accumulated as NO gas at ~6 μg-N/kg-refuse·h^-1) to a lesser extent than OTC-amended samples. Further, deep sequencing results show that long-term OTC exposure partially substituted Hyphomicrobium, Fulvivirga, and Caldilinea (>5%) for the dominant bacterial hosts (Rhodothermus, ~20%) harboring nosZ and norB genes that significantly correlated with nitrogen emission pattern, while sulfamethazine amendment completely reduced the relative abundance of the "original inhabitants" functioning to produce NO_x gas reduction. The main ARG carriers (Pseudomonas) that were substantially enriched in the SMT group had lower levels of denitrifying functional genes, which could imply that denitrification is influenced more by bacterial dynamics than by abundance of ARGs under antibiotic pressures.

Detection, Occurrence and Fate of Emerging Contaminants in Agricultural Environments

A total of 59 papers published in 2015 were reviewed ranging from detailed descriptions of analytical methods, to fate and occurrence studies, to ecological effects and sampling techniques for a wide variety of emerging contaminants likely to occur in agricultural environments. New methods and studies on veterinary pharmaceuticals, steroids, antibiotic resistance genes in agricultural environments continue to expand our knowledge base on the occurrence and potential impacts of these compounds. This review is divided into the following sections: Introduction, Analytical Methods, Steroid Hormones, Pharmaceutical Contaminants, Transformation Products, and "Antibiotic Resistance, Drugs, Bugs and Genes".