The effect of environmental and therapeutic concentrations of antibiotics on nitrate reduction rates in river sediment

Identifying groundwater anthropogenic disturbances and their predominant impact on microbial nitrogen cycling at a former contamination site adjacent to Baiyangdian Lake

Groundwater ecosystems face increasing threat from declining water quality due to intensified urbanization, agricultural, and industrial activities. Accurately identifying anthropogenic disturbances remains challenging, and their effects on microbial nitrogen cycling are still largely unknown. Here, by collecting 64 groundwater samples from an aquifer beneath the Tanghe sewage reservoir in the North China Plain, we conducted a full-spectrum screening of 228 physiochemical indices, 47 nitrogen cycling genes (NCGs) and 2182 metagenome-assembled genomes (MAGs) harboring NCGs. Unmix model identified antibiotic usage, industrial manufacturing, and agricultural practices as the predominant pollution sources, explaining 49.6-92.2 % (averaged 81.0 %) of the variations in aquifer attributes. These activities were primary drivers governing distributions of groundwater NCGs and NCG-hosts, with fragmented denitrification processes being prevalent. Antibiotic usage and industrial activities were probably associated with suppressed nitrogen cycling, while agriculture had a positive effect. Notably, we observed enhanced mutualistic interactions within NCG-hosts and increased enrichment of NCG-antibiotic resistance gene (ARG), NCG-mental resistance gene (MRG), and NCG-ARG-MRG co-hosts under high anthropogenic stresses, suggesting microbial adaptation to optimize nutrient and energy metabolism. This study provided new insight into how groundwater nitrogen cycling responds to anthropogenic disturbances, offering valuable information for developing groundwater management and pollution control strategies.

Nanopaper Integrated Smart Device: An Opto-Electrochemical Biosensor for Real-Time Dual On-Field Detection of Organophosphorus Pesticides

The frequent and excessive use of organophosphorus pesticides in the agriculture industry raises persistent concerns regarding their environmental protection and public health implications. Addressing these issues requires the development of affordable and reliable sensing platforms for on-field monitoring to mitigate their adverse impacts promptly. This study utilizes nanocellulose papers (bacterial and TEMPO-oxidized) combined with butyrylcholinesterase to create a novel reagent-free and orthogonal nanobioplatform featuring smart opto-electrochemical dual outputs. An integrated nano-PAD, preloaded with enzymes and enzymatic substrates, is fabricated using wax-printing and screen-printing technologies. The nano-PAD measures opto-electroactive products, specifically indoxyl and thiocholine, whose concentrations correlate directly with the enzymatic inhibition caused by paraoxon, used as the organophosphate model. To enhance user convenience and meet the requirements for smart real-time point-of-need detection, integration of the nano-PAD with a smartphone-operated miniaturized potentiostat and a self-developed portable smart optical reader is achieved. The developed bioanalytical platform, further supported by a self-developed Android application, enables accurate and efficient quantification of dual signals in real time. The system covers a wide detection range of paraoxon (20-100 ppb) and demonstrates reliable recovery levels (ranging from 98 to 107%) in a real matrix, specifically wastewater. Given these demonstrated capabilities, this innovative biosensing strategy holds substantial potential for practical application in environmental surveillance, facilitating timely and informed environmental management decisions, particularly in resource-limited settings where traditional analytical tools are inaccessible.

Bio-degraded of sulfamethoxazole by microbial consortia without addition nutrients: Mineralization, nitrogen removal, and proteomic characterization

Sulfamethoxazole (SMX) is widely employed as an antibiotic, while its residue in environment has become a common public concern. Using 100 mg/L SMX as the sole nutrient source, the acclimated sludge obtained by this study displayed an excellent SMX degradation performance. The addition of SMX resulted in significant microbiological differentiation within the acclimated sludge. Microbacterium (6.6%) was identified as the relatively dominant genera in metabolism group that used SMX as sole carbon source. Highly expressed proteins from this strain strongly suggested its essential role in SMX degradation, while the degradation of SMX by other strains (Thaurea 78%) in co-metabolism group appeared to also rely on this strain. The interactions of differentially expressed proteins were primarily involved in metabolic pathways including TCA cycle and nitrogen metabolism. It is concluded that the sulfonamides might serve not only as the carbon source but also as the nitrogen source in the reactor. A total of 24 intermediates were identified, 13 intermediates were newly reported. The constructed pathway suggested the mineralizing and nitrogen conversion ability towards SMX. Batch experiments also proved that the acclimated sludge displayed ability to biodegrade other sulfonamides, including SM2 and SDZ and SMX-N could be removed completely.

Comprehensive metagenomic and enzyme activity analysis reveals the inhibitory effects and potential toxic mechanism of tetracycline on denitrification in groundwater

The widespread use of tetracycline (TC) inevitably leads to its increasing emission into groundwater. However, the potential risks of TC to denitrification in groundwater remain unclear. In this study, the effects of TC on denitrification in groundwater were systematically investigated at both the protein and gene levels from the electron behavior aspect for the first time. The results showed that increasing TC from 0 to 10 µg·L-1 decreased the nitrate removal rate from 0.41 to 0.26 mg·L-1·h-1 while enhancing the residual nitrite concentration from 0.52 mg·L-1 to 50.60 mg·L-1 at the end of the experiment. From a macroscopic view, 10 µg·L-1 TC significantly inhibited microbial growth and altered microbial community structure and function in groundwater, which induced the degeneration of denitrification. From the electron behavior aspect (the electron production, electron transport and electron consumption processes), 10 µg·L-1 TC decreased the concentration of electron donors (nicotinamide adenine dinucleotide, NADH), electron transport system activity, and denitrifying enzyme activities at the protein level. At the gene level, 10 µg·L-1 TC restricted the replication of genes related to carbon metabolism, the electron transport system and denitrification. Moreover, discrepant inhibitory effects of TC on individual denitrification steps, which led to the accumulation of nitrite, were observed in this study. These results provide the information that is necessary for evaluating the potential environmental risk of antibiotics on groundwater denitrification and bring more attention to their effects on geochemical nitrogen cycles.

Unveiling different antibiotic degradation mechanisms on dual reaction center catalysts with nitrogen vacancies via peroxymonosulfate activation

Metal-nitrogen-site catalysts are widely recognized as effective heterogeneous catalysts in peroxymonosulfate (PMS)-based advanced oxidation processes. However, the selective oxidation mechanism for organic pollutants is still contradictory. In this work, manganese-nitrogen active centers and tunable nitrogen vacancies were synchronously constructed on graphitic carbon nitride (LMCN) through l-cysteine-assisted thermal polymerization to reveal different antibiotic degradation mechanisms. Benefiting from the synergism of manganese-nitrogen bond and nitrogen vacancies, the LMCN catalyst exhibited excellent catalytic activity for the degradation of tetracycline (TC) and sulfamethoxazole (SMX) antibiotics with first-order kinetic rate constants of 0.136 min^-1 and 0.047 min^-1, which were higher than those of other catalysts. Electron transfer dominated TC degradation at low redox potentials, while electron transfer and high-valent manganese (Mn (V)) were responsible for SMX degradation at high redox potentials. Further experimental studies unveiled that the pivotal role of nitrogen vacancies is to promote electron transfer pathway and Mn(V) generation, while nitrogen-coordinated manganese as the primary catalytic active site determines Mn(V) generation. In addition, the antibiotic degradation pathways were proposed and the toxicity of byproducts was analyzed. This work provides an inspiring idea for the controlled generation of reactive oxygen species by targeted activation of PMS.

Fate and transport of tetracycline and ciprofloxacin and impact on nitrate reduction activity in coastal sediments from the Seine Estuary, France

Fluoroquinolones and tetracyclines are frequently detected antibiotics in aquatic sediments. In this study, the transport of ciprofloxacin (CIP) and tetracycline (TET) was investigated in sediments from the Seine Estuary (France), under nitrate reducing conditions. Dynamic flow experiments showed that although TET and CIP strongly interacted with the sediment components through adsorption and (bio)-chemical transformation, they kept their antimicrobial activities. Less nitrate reduction was observed during the first period of breakthrough, while TET and CIP were absent in the column effluent. Batch experiments with freeze-dried vs fresh sediments showed that adsorption and abiotic degradation are the major removal processes, while microbe-driven transformation is of less importance. Whereas TET is to a large extent chemically transformed and little adsorbed in the sediment, CIP was less transformed and more adsorbed, most likely due to the great reactivity of TET with redox-active mineral surfaces. Our findings show the strong capacity of natural sediment to retain and transform antibiotics, while still maintaining their antimicrobial activity or inhibitory effect of nitrate reducing activity.

Role of iron(II) sulfide in autotrophic denitrification under tetracycline stress: Substrate and detoxification effect

Autotrophic denitrification using inorganic compounds as electron donors has gained increasing attention in the field of wastewater treatment due to its numerous advantages, such as no need for exogenous organic carbon, low energy input, and low sludge production. Tetracycline (TC), a refractory contaminant, is often found coexisting with nutrients (NO₃^- and PO₄^3-) in wastewater, which can negatively affect the biological nutrient removal process because of its biological toxicity. However, the performance of autotrophic denitrification under TC stress has rarely been reported. In this study, the effects of TC on autotrophic denitrification with thiosulfate (Na₂S₂O₃) and iron (II) sulfide (FeS) as the electron donors were investigated. With Na₂S₂O₃ as the electron donor, TC slowed down the nitrate removal rate, which decreased from 1.32 to 0.18 d^-1, when TC concentration increased from 0 mg/L to 50 mg/L. When TC concentration was higher than 2 mg/L, nitrite reduction was seriously inhibited, leading to nitrite accumulation. With FeS as the electron donor, nitrate removal was much more efficient under TC-stressed conditions, and no distinct nitrite accumulation was observed when the initial TC concentration was as high as 10 mg/L, indicating the effective detoxification of FeS. The detoxification effects in the FeS autotrophic denitrification system mainly resulted from the rapid adsorption of TC by FeS and effective degradation of TC, as proven by a relatively higher living biomass area. This study offers new insights into the response of sulfur-based autotrophic denitrifiers to TC stress and demonstrates that the FeS-based autotrophic denitrification process is a promising technology for the treatment of wastewater containing emerging contaminants and nutrients.

Ecological Responses of Maize Rhizosphere to Antibiotics Entering the Agricultural System in an Area with High Arsenicals Geological Background

Metal(loid)s can promote the spread and enrichment of antibiotic resistance in the environmental ecosystem through a co-selection effect. Little is known about the ecological effects of entering antibiotics into the environment with long-term metal(loid)s' resistance profiles. Here, cow manure containing oxytetracycline (OTC) or sulfadiazine (SA) at four concentrations (0 (as control), 1, 10, and 100 mg/kg) was loaded to a maize cropping system in an area with high a arsenicals geological background. Results showed that exogenous antibiotics entering significantly changed the nutrient conditions, such as the concentration of nitrate nitrogen, ammonium nitrogen, and available phosphorus in the maize rhizosphere soil, while total arsenic and metals did not display any differences in antibiotic treatments compared with control. Antibiotics exposure significantly influenced nitrate and nitrite reductase activities to reflect the inhibition of denitrification rates but did not affect the soil urease and acid phosphatase activities. OTC treatment also did not change soil dehydrogenase activities, while SA treatment posed promotion effects, showing a tendency to increase with exposure concentration. Both the tested antibiotics (OTC and SA) decreased the concentration of arsenite and arsenate in rhizosphere soil, but the inhibition effects of the former were higher than that of the latter. Moreover, antibiotic treatment impacted arsenite and arsenate levels in maize root tissue, with positive effects on arsenite and negative effects on arsenate. As a result, both OTC and SA treatments significantly increased bioconcentration factors and showed a tendency to first increase and then decrease with increasing concentration. In addition, the treatments decreased translocation capacity of arsenic from roots to shoots and showed a tendency to increase translocation factors with increasing concentration. Microbial communities with arsenic-resistance profiles may also be resistant to antibiotics entering.

Transformation of sulfamethoxazole by sulfidated nanoscale zerovalent iron activated persulfate: Mechanism and risk assessment using environmental metabolomics

The threat caused by the misuse of antibiotics to ecology and human health has been aroused an extensive attention. Developing cost-effective techniques for removing antibiotics needs to put on the agenda. In current research, the degradation mechanism of sulfamethoxazole (SMX) by sulfidated nanoscale zerovalent iron (S-nZVI) driven persulfate, together with the potential risk of intermediates were studied. The degradation of SMX followed a pseudo-first order kinetics reaction with k_obs at 0.1176 min^-1. Both SO₄^•- and •OH were responsible for the degradation of SMX, and SO₄^•- was the predominant free radical. XPS analysis demonstrated that reduced sulfide species promoted the conversion of Fe (III) to Fe (II), resulting in the higher transformation rate of SMX. Six intermediates products were generated through hydroxylation, dehydration condensation, nucleophilic reaction, and hydrolysis. The risk of intermediates products is subsequently assessed using E. coli as a model microorganism. After E.coli exposure to intermediates for 24 h, the upmetabolism of carbohydrate, nucleotide, citrate acid cycle and downmetabolism of glutathione, sphingolipid, galactose by metabolomics analysis identified that SMX was effectively detoxified by oxidation treatment. These findings not only clarified the superiority of S-nZVI/persulfate, but also generated a novel insight into the security of advanced oxidation processes.

Effect of sulfamethoxazole on nitrate removal by simultaneous heterotrophic aerobic denitrification

The increase in mariculture activities worldwide has not only led to a rise of nitrogen compounds in the ecosystem but has also intensified the accumulation of antibiotics in both terrestrial and marine environments. This study focused on the effect of typical antibiotics, specifically sulfamethoxazole (SMX) on nitrate removal from mariculture wastewater by aerobic denitrification process; an aerobic denitrification system feeding with 148.2 mg/L COD, 8.59 mg/L nitrate, 0.72 mg/L nitrite, and 4.75 mg/L ammonium was set up. The hydraulic retention time (HRT) was 8 h. As the aerobic bioreactor started up successfully without SMX dosage, an excellent removal of ammonium, nitrite, and nitrate was achieved at 91.35%, 93.33%, and 88.51%, respectively; the corresponding effluent concentrations were 0.41 mg/L, 0.048 mg/L, and 0.96 mg/L. At the influent SMX doses of 0, 1, 5, and 10 mg/L, the COD removal reached 96.91%, 96.27%, 88.69%, and 85.89%, resulting in effluent concentrations of 4.53, 5.45, 17.38, and 20.6 mg/L, respectively. Nitrification was not inhibited by SMX dosage. However, aerobic denitrification was inhibited by 10 mg/L SMX. Proteobacteria was the most abundant phylum, and surprisingly its abundance increased with the increase in SMX concentration. An excellent SMX degradation was noted at initial SMX dosages of 1, 5, and 10 mg/L; the removal rate was 100%,100%, and 99.8%, respectively. The SMX degrading genera Comamonas sp., Acinetobacter sp., and Thauera sp. are of great validity to wastewater engineers because they have demonstrated efficiency in simultaneous heterotrophic aerobic denitrification and antibiotic degradation as well as COD removal. PRACTITIONER POINTS: Nitrification was not inhibited by increase in SMX dosage. An increase in SMX dosage inhibited aerobic denitrification. COD removal was not affected by increased SMX dosage. Comamonas, Acinetobacter, and Thauera had high efficiency in COD removal and SMX degradation.

Sediments alleviate the inhibition effects of antibiotics on denitrification: Functional gene, microbial community, and antibiotic resistance gene analysis

Both antibiotics and sediments can affect the denitrification in aquatic systems. However, little is known how antibiotics influence the denitrification in the presence of sediments. Here, the effects of antibiotics (sulfamethoxazole, tetracycline and ofloxacin) on denitrification in the absence and presence of sediments were investigated. The influencing mechanisms were revealed by quantifying the denitrification functional genes (DNGs), 16S-seq of bacteria, and antibiotic resistance genes (ARGs). The results showed that the presence of antibiotics inhibited NO₃-N reduction by decreasing the abundances of narG, nirK, nosZ, total DNGs, and denitrifying bacteria. However, the inhibition effect was alleviated by sediments, which promoted the growth of bacteria and decreased the selective pressure of antibiotics as the vector of bacteria and antibiotics, thus increasing the abundances of denitrifying bacteria and all the DNGs. Partial least-squares path model disclosed that antibiotics had negative effects on bacteria, ARGs and DNGs, while sediments had negative effects on ARGs but positive effects on bacteria and DNGs. The network analysis further revealed the close relation of the genera Bacillus, Acinetobacter, and Enterobacter with the ARGs and DNGs. The findings are helpful to understand the denitrification in antibiotic-polluted natural waters.

Antibiotic residues in environment: antimicrobial resistance development, ecological risks, and bioremediation

The overuse of antibiotics and their disposal without processing are leading the environment and its inhabitants towards a serious health emergency. There is abundance of diverse antibiotic resistance genes and bacteria in environment, which demands immediate attention for the effective removal of antibiotics. There are physical and chemical methods for removal, but the generation of toxic byproducts has directed the efforts towards bioremediation for eco-friendly and sustainable elimination of antibiotics from the environment. Various effective and reliable bioremediation approaches have been used, but still antibiotic residues pose a major global threat. Recent developments in molecular and synthetic biology might offer better solution for engineering of microbe-metabolite biodevices and development of novel strains endowed with desirable properties. This review summarizes the impact of antibiotics on environment, mechanisms of resistance development, and different bioremediation approaches.

Effects of sulfamethoxazole on coupling of nitrogen removal with nitrification in Yangtze Estuary sediments

Coupling of nitrogen removal processes with nitrification (NR_n) are vital synergistic nitrogen elimination mechanisms in aquatic environments. However, the effects of antibiotics on NR_n are not well known. In the present work, 20-day continuous-flow experiments combined with ¹⁵N tracing techniques and quantitative PCR were performed to simulate the impact of sulfamethoxazole (SMX, a sulfonamide antibiotic) with near in situ concentration on NR_n processes in sediments of Yangtze Estuary. Results showed that SMX with near in situ concentration significantly decreased NR_n, NR_w (uncoupling of nitrogen removal processes with nitrification) and actual nitrogen removal rates via inhibiting nitrogen transformation functional genes (AOB, narG, nirS, nosZ) and anammox 16S rRNA gene, while the coupling links between nitrification and nitrogen removal processes were not broken by the exposure. The proportion of NR_n in total nitrogen removal processes decreased by approximately 10% with SMX addition, due to the different inhibition on AOB, denitrifying genes and anammox 16S rRNA gene. N₂O production and nitrite accumulation remarkably increased with SMX addition under simultaneous nitrification and denitrification, and they strongly correlated with each other. The more severely inhibition on nirS gene (13.6-19.8%) than Nitrospira nxrB gene (0.3-8.2%) revealed that the increased nitrite accumulation with SMX addition mainly occurred in heterotrophic denitrification, suggesting that the increased N₂O production was dominated by the heterotrophic nitrite reduction. Moreover, we estimated that the ratio of external inorganic N eliminated by actual nitrogen removal can upgrade to 6.4-7.4% under circumstances of no inhibition by SMX. This study revealed the effects of SMX with near in situ concentration on NR_n processes and illustrated the microbial mechanism on functional genes level. Our results highlighted the inhibitory effects of SMX on NR_n may contribute to reactive N retention and N₂O production in estuarine and coastal ecosystems.

Effects of antibiotic norfloxacin on the degradation and enantioselectivity of the herbicides in aquatic environment

Antibiotics are currently extensively used in human medicine, animal farming, agriculture and aquaculture, and their residue has become a global environmental problem. However, the effects of antibiotic on other pollutants in aquatic environment are still poorly understood. In this study, the influences of norfloxacin on the residue, degradation and distribution of the herbicides (simazine, atrazine, terbuthylazine, acetochlor and metolachlor) and the enantioselectivity of acetochlor in sediment and water-sediment microcosm system were investigated. Sediment was spiked with norfloxacin and water was contaminated by herbicides to simulate environmental pollution. The amounts of herbicides in water and sediment samples were analyzed within 30 days of cultivation. The results showed that norfloxacin could significantly inhibit the dissipation, lengthen the half-lives and enhance the residues of herbicides in sediment. Take simazine as an example, its half-life significantly increased from 16.1 days to 19.3 days and its residual percentage grew from 24.2% to 30.4% when sediment was contaminated with 5 mg·kg^-1 norfloxacin. However, only acetochlor degradation was significantly inhibited by norfloxacin in water-sediment microcosm and the distribution of the herbicides were not affected. Enantioselective degradation of acetochlor was observed both in control and norfloxacin-treated water-sediment system, with R-acetochlor preferential elimination, suggesting the co-existence of norfloxacin had very limited influence on the enantioselectivity. The findings indicated that co-contamination with norfloxacin could increase the persistence of herbicides in aquatic environment, thus increasing the environmental risks to aquatic organisms.

Transcriptomic Analysis of Staphylococcus aureus Under the Stress Condition Caused by Litsea cubeba L. Essential Oil via RNA Sequencing

Litsea cubeba L. essential oil (LCEO) is a natural essential oil with considerable antimicrobial activity, and it can gradually replace some chemical additives in the food industry. However, the genetic evidences of stress response of bacteria under sub-lethal treatment with LCEO is limited. To this end, transcriptomic analysis of Staphylococcus aureus 29213 under a low concentration of LCEO was performed. Bacterial RNA samples were extracted from 1/4 MIC (0.07 μL/mL) of LCEO-treated and non-treated S. aureus 29213. The transcriptional results were obtained by RNA sequencing (RNA-Seq). After treated with LCEO of S. aureus 29213, 300, and 242 genes were significantly up and down-regulated. Up-regulated genes were mainly related to cell membrane (wall) stress stimulon including genes related to two-component regulatory system (VraS), histidine metabolism (hisABCD etc.) and L-lysine biosynthesis (thrA, lysC, asd etc.). Significant differences were also founded between LCEO-treated and non-treated groups in peptidoglycan biosynthesis related pathways. Down-regulated genes were related to nitrogen metabolism (NarGHIJ etc.), carotenoid biosynthesis (all) and pyruvate metabolism (phdA, pflB, pdhC etc.) of S. aureus 29213 in an LCEO-existing environment compared to the control. At the same time, we confirmed that LCEO can significantly affect the staphyloxanthin level of S. aureus 29213 for the first time, which is closely related to the redox state of S. aureus 29213. These evidences expanded the knowledge of stress response of S. aureus 29213 strain under sub-lethal concentration of LCEO.

Co-occurrence characteristics of antibiotics and estrogens and their relationships in a lake system affected by wastewater

Antibiotics and estrogens are recognized as emerging contaminants in the water environment because of their potentially adverse effects on aquatic ecosystems. The concentrations of four steroid estrogens (17α-estradiol, 17β-estradiol, estrone, and estriol) and eight antibiotics (norfloxacin, levofloxacin, ciprofloxacin, enrofloxacin, metronidazole, sulfapyridine, doxycycline, and sulfamethoxazole) in the Chaohu Lake basin in Anhui province, China, were analyzed along with adjacent wastewater. The levels of the target antibiotics and estrogens were below detection limits (not detected [nd])-89.86 and nd-118.09 ng L^-1 , respectively, in the lake water. All of the target antibiotics and estrogens were detected in sediment, and the concentrations ranged widely (nd-35,544 and nd-16,344 ng kg^-1 , respectively). Antibiotics and estrogens varied spatially in the study area and mostly came from untreated wastewater. Antibiotics and estrogens were associated with water parameters such as pH and total nitrogen. A significant positive correlation was observed between estriol and levofloxacin concentrations (r = .65; p < .01), indicating that levofloxacin from the same source might have inhibited the microbiological degradation of estriol in the surface water. Overall, the estrogens pose a more severe risk than antibiotics to the Chaohu Lake system. However, co-occurrence of antibiotics may affect the fate of estrogens in the same lake media. More attention should be given to estrogens than to antibiotics in wastewater-affected lake systems.

Silver nanoparticles and Fe(III) co-regulate microbial community and N2O emission in river sediments

The effects of environmental concentration silver nanoparticles (ecAgNPs) on microbial communities and the nitrogen cycling in river sediments remain largely uncharacterized. As a fundamental component of sediments, Fe(III) can interact with AgNPs and participate in nitrogen transformation processes. N₂O is an important intermediate in nitrogen transformation processes and can be a potent greenhouse gas with significant environmental effects. However, the impacts of the co-existence of AgNPs and Fe(III) on microbial communities and N₂O emission in river sediments are still unclear. In the present study, mesocosm experiments were conducted to assess the changes of microbial communities and N₂O emission in response to the co-existence of AgNPs and environmental concentration Fe(III). Our results revealed that the microbial community diversity and N₂O emission in river sediments responded differently to ecAgNPs (0.05 mg/kg) and high-polluting concentration AgNPs (hcAgNPs, 5 mg/kg), which was further regulated by the environmental concentration Fe(III) (1 mg/g and 10 mg/g). After ecAgNPs treatments, a marked increase was observed in microbial diversity compared to hcAgNPs treatments, regardless of the Fe(III) concentration in the sediment. The β-NTI index indicated that AgNPs had stronger impacts on phylogenetic distance of bacterial communities in sediments containing 1 mg/g Fe(III) than that containing 10 mg/g Fe(III). In sediments containing 1 mg/g Fe(III), ecAgNPs did not affect N₂O emission, but hcAgNPs significantly inhibited the emission of N₂O. However, in sediments containing 10 mg/g Fe(III), N₂O emission was significantly stimulated upon exposure to ecAgNPs, but the inhibition effect of hcAgNPs was barely observed. Functional prediction and real-time PCR analyses indicated that AgNPs and Fe(III) predominantly affected N₂O emissions by affecting the abundance of the nirK gene. Our results provide new insights into the ecological impacts of the co-existence of environmental concentration AgNPs and Fe(III) in altering microbial communities and nitrogen transformation functions in river sediments.

A novel discovery of a heterogeneous Fenton-like system based on natural siderite: A wide range of pH values from 3 to 9

Natural iron-bearing minerals have been proven to be effective for activating H₂O₂ to produce OH, which can be used to degrade organic pollutants. In this study, the performance of siderite to degrade sodium sulfadiazine via catalytic H₂O₂ degradation was investigated at different solution pH values from 3 to 9. An interesting discovery was made: the performance of the siderite-H₂O₂ system was excellent under acidic, neutral, and even alkaline conditions. The influence of various factors (e.g. initial concentration, anions, natural organic matters, etc.) on the system under different pH conditions was investigated, which confirmed that siderite exhibited an excellent catalytic performance. By combining EPR characterization with scavenger research, it was proposed that dissolved iron (Fe²⁺) mainly initiated the homogenous Fenton reaction to degrade pollutants under acidic conditions, while structural Fe²⁺ species present in siderite triggered Fenton-like reactions under neutral or even alkaline conditions. From the SEM and XPS characterizations, oxidation and dissolution of Fe²⁺ on the surface were also observed, confirming our inference concerning the different reaction mechanisms. The experimental findings show that this siderite-H₂O₂ system can be used in solutions with pH values from 3 to 9 and that siderite plays a positive role in soil and groundwater remediation when H₂O₂ is used as an oxidant.

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.

Trends in the occurrence and risk assessment of antibiotics in shallow lakes in the lower-middle reaches of the Yangtze River basin, China

Antibiotics have become a global public concern because of their extensively usage and high toxicity on aquatic organisms, especially leading to the widespread of antibiotic resistance genes. The objective of this study was to evaluate the occurrence, spatial distribution and ecological risks of multi-classes commonly used human and veterinary antibiotics in both aqueous and sedimentary phases of 65 shallow lakes in the lower-middle reaches of the Yangtze River, China. In the target area, antibiotic concentrations in most of lakes (<20 ng/L in the water of 22 lakes and <20 ng/g in the sediments of 43 lakes) were generally lower than those documented in previous studies in China and other countries, and these differences were probably due to less pollutant sources, high temperatures and heavy rainfall in summer. The concentrations of antibiotics in water (>100 ng/L) or sediments (>100 ng/g) of nine lakes, such as Dianshan Lake, Ge Lake and Ce Lake, were comparable to those in rivers and lakes that were seriously polluted by urban and livestock wastewater in China. The Taihu lakes showed relatively higher antibiotic concentrations, followed by the Huaihe River lakes, Poyang lakes and Dongting lakes. The composition of antibiotics showed that agricultural source might be the main source of antibiotics in most of the lakes in the lower-middle reaches of the Yangtze River basin, China. The pseudo distribution coefficient (P-K_d) and significant relationship between antibiotics and environmental factors in the present study suggested the spatial of antibiotics in the lakes might be affected by antibiotics' physiochemical properties and environmental factors. The environmental risk assessment results showed that in general, sulfamethoxazole (SMX), erythromycin (ETM) and ofloxacin (OFX) in the surface water could pose medium risks to algae or bacteria in the aquatic ecosystem, while antibiotics ETM, roxithromycin (RTM), enrofloxacin (EFX) and sulfadiazine (SDZ) in the sediment might pose medium risks to algae or bacteria populations. High potential risk might occur in winter in most lakes due to lower water storage and less degradation. Overall, our study reveals the pollution trends and potential sources of antibiotics in shallow lakes in the lower-middle reaches of the Yangtze River basin.

Sensitivity assessment of denitrifying bacteria against typical antibiotics in groundwater

The effects of antibiotics on nitrate denitrification in groundwater have acquired growing concern. Denitrification is a microbially mediated process. The effects of antibiotics on denitrification were mainly reflected in denitrifying bacteria. However, little is known about the relationship between antibiotics and denitrifying bacteria. Based on this, both direct antimicrobial susceptibility testing and microbial batch-culture experiments were conducted to assess the influences of typical antibiotics on denitrifying groundwater bacteria, mainly Pseudomonas (46.17%). Denitrifying bacteria, screened from a long-term groundwater denitrification environment, were tested for sensitivity to five typical antibiotics in groundwater: sulfamethoxazole (SMX), erythromycin (ERY), enrofloxacin (ENR), clindamycin (CLI), and tetracycline (TCY). The results showed that the sensitivity of denitrifying bacteria to antibiotics is mainly related to the type and concentration of antibiotics. For antibiotic types, the order of sensitivity by quantitative assessment is ENR > TCY > SMX > ERY > CLI. Fluoroquinolones (FQs) represented by ENR were selected to explore their concentration effects. The influences on denitrifying bacteria were divided into the high concentration effect (500 μg L-1 to 100 mg L-1) and the low concentration effect (100 ng L-1 to 10 μg L-1) with about 100 μg L-1 as a boundary. Exposure to high concentrations had significant inhibitory effects on bacterial growth and exhibited dose dependency, especially for ciprofloxacin (CIP). The low concentration effect was independent of concentration, which may be stimulation or inhibition. The stimulation mainly occurred due to ENR-exposure. For inhibitory effects, Lomefloxacin (LOM) was more effective than other FQs. Especially for inhibition at ng-level exposure, LOM and norfloxacin (NOR) exposures led to the highest and lowest inhibition rates, respectively.

Cometabolic biotransformation and microbial-mediated abiotic transformation of sulfonamides by three ammonia oxidizers

The abilities of three phylogenetically distant ammonia oxidizers, Nitrososphaera gargensis, an ammonia-oxidizing archaeon (AOA); Nitrosomomas nitrosa Nm90, an ammonia-oxidizing bacterium (AOB); and Nitrospira inopinata, the only complete ammonia oxidizer (comammox) available as a pure culture, to biotransform seven sulfonamides (SAs) were investigated. The removals and protein-normalized biotransformation rate constants indicated that the AOA strain N. gargensis exhibited the highest SA biotransformation rates, followed by N. inopinata and N. nitrosa Nm90. The transformation products (TPs) of sulfadiazine (SDZ), sulfamethazine (SMZ) and sulfamethoxazole (SMX) and the biotransformation mechanisms were evaluated. Based on the analysis of the TP formulas and approximate structures, it was found that during biotransformation, i) the AOA strain carried out SA deamination, hydroxylation, and nitration; ii) the AOB strain mainly performed SA deamination; and iii) the comammox isolate participated only in deamination reactions. It is proposed that deamination was catalyzed by deaminases while hydroxylation and nitration were mediated by nonspecific activities of the ammonia monooxygenase (AMO). Additionally, it was demonstrated that among the three ammonia oxidizers, only AOB contributed to the formation of pterin-SA conjugates. The biotransformation of SDZ, SMZ and SMX occurred only when ammonia oxidation was active, suggesting a cometabolic transformation mechanism. Interestingly, SAs could also be transformed by hydroxylamine, an intermediate of ammonia oxidation, suggesting that in addition to enzymatic conversions, a microbially induced abiotic mechanism contributes to SA transformation during ammonia oxidation. Overall, using experiments with pure cultures, this study provides important insights into the roles played by ammonia oxidizers in SA biotransformation.

Evaluating the net effect of sulfadimidine on nitrogen removal in an aquatic microcosm environment

Antibiotics enter into aquatic pond sediments by wastewater and could make detrimental effects on microbial communities. In this study, we examined the effects of sulfadimidine on nitrogen removal when added to experimental pond sediments. We found that sulfadimidine increased the number of sulfadimidine resistant bacteria and significantly increased the abundance of sul2 at the end of the incubation time (ANOVA test at Tukey HSD, P < 0.05). In addition, sulfadimidine decreased the N₂O reduction rate as well as the amount of nitrate reduction. Pearson correlation analysis revealed that the N₂O reduction rate was significantly and negatively correlated with narG (r = -0.679, P < 0.05). In contrast, we found a significant positive correlation between the amount of nitrate reduction and the abundance of narG (r = 0.609, P < 0.05) and nirK (r = 0.611, P < 0.05). High-throughput sequencing demonstrated that Actinobacteria, Euryarchaeota, Gemmatimonadetes, Nitrospirae, Burkholderiaceae (a family of Proteobacteria), and Thermoanaerobaculaceae (a family of Firmicutes) decreased with sulfadimidine exposure. In sediments, Actinobacteria, Bacteroidetes, Cyanobacteria, Epsilonbacteraeota, Euryarchaeota, Firmicutes, Gemmatimonadetes, and Spirochaetesat may play key roles in nitrogen transformation. Overall, the study exhibited a net effect of antibiotic exposure regarding nitrogen removal in an aquatic microcosm environment through a combination of biochemical pathways and molecular pathways, and draws attention to controlling antibiotic pollution in aquatic ecosystems.

Motility of Shewanella oneidensis MR-1 Allows for Nitrate Reduction in the Toxic Region of a Ciprofloxacin Concentration Gradient in a Microfluidic Reactor

Subsurface environments often contain mixtures of contaminants in which the microbial degradation of one pollutant may be inhibited by the toxicity of another. Agricultural settings exemplify these complex environments, where antimicrobial leachates may inhibit nitrate bioreduction, and are the motivation to address this fundamental ecological response. In this study, a microfluidic reactor was fabricated to create diffusion-controlled concentration gradients of nitrate and ciprofloxacin under anoxic conditions in order to evaluate the ability of Shewanella oneidenisis MR-1 to reduce the former in the presence of the latter. Results show a surprising ecological response, where swimming motility allow S. oneidensis MR-1 to accumulate and maintain metabolic activity for nitrate reduction in regions with toxic ciprofloxacin concentrations (i.e., 50× minimum inhibitory concentration, MIC), despite the lack of observed antibiotic resistance. Controls with limited nutrient flux and a nonmotile mutant (Δ flag) show that cells cannot colonize antibiotic rich microenvironments, and this results in minimal metabolic activity for nitrate reduction. These results demonstrate that under anoxic, nitrate-reducing conditions, motility can control microbial habitability and metabolic activity in spatially heterogeneous toxic environments.

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.

Transcriptomics Study on Staphylococcus aureus Biofilm Under Low Concentration of Ampicillin

Staphylococcus aureus is one of the representative foodborne pathogens which forms biofilm. Antibiotics are widely applied in livestock husbandry to maintain animal health and productivity, thus contribute to the dissemination of antimicrobial resistant livestock and human pathogens, and pose a significant public health threat. Effect of antibiotic pressure on S. aureus biofilm formation, as well as the mechanism, remains unclear. In this study, the regulatory mechanism of low concentration of ampicillin on S. aureus biofilm formation was elucidated. The viability and biomass of biofilm with and without 1/4 MIC ampicillin treatment for 8 h were determined by XTT and crystal violet straining assays, respectively. Transcriptomics analysis on ampicillin-induced and non-ampicillin-induced biofilms were performed by RNA-sequencing, differentially expressed genes identification and annotation, GO functional and KEGG pathway enrichment. The viability and biomass of ampicillin-induced biofilm showed dramatical increase compared to the non-ampicillin-induced biofilm. A total of 530 differentially expressed genes (DEGs) with 167 and 363 genes showing up- and down-regulation, respectively, were obtained. Upon GO functional enrichment, 183, 252, and 21 specific GO terms in biological process, molecular function and cellular component were identified, respectively. Eight KEGG pathways including "Microbial metabolism in diverse environments", "S. aureus infection", and "Monobactam biosynthesis" were significantly enriched. In addition, "beta-lactam resistance" pathway was also highly enriched. In ampicillin-induced biofilm, the significant up-regulation of genes encoding multidrug resistance efflux pump AbcA, penicillin binding proteins PBP1, PBP1a/2, and PBP3, and antimicrobial resistance proteins VraF, VraG, Dlt, and Aur indicated the positive response of S. aureus to ampicillin. The up-regulation of genes encoding surface proteins ClfB, IsdA, and SasG and genes (cap5B and cap5C) which promote the adhesion of S. aureus in ampicillin induced biofilm might explain the enhanced biofilm viability and biomass.

UPLC-MS/MS analysis of antibiotics in pharmaceutical effluent in Tunisia: ecotoxicological impact and multi-resistant bacteria dissemination

The UPLC MS/MS analysis showed the presence of the two antibiotics in the pharmaceutical industry discharges during 3 months; norfloxacin and spiramycin which were quantified with the mean concentrations of 226.7 and 84.2 ng mL^-1, respectively. Sixteen resistant isolates were obtained from the pharmaceutical effluent and identified by sequencing. These isolates belong to different genera, namely Citrobacter, Acinetobacter, Pseudomonas, Delftia, Shewanella, and Rheinheimera. The antibiotic resistance phenotypes of these isolates were determined (27 tested antibiotics-discs). All the studied isolates were found resistant to amoxicillin and gentamicin, and 83.33% of isolates were resistant to ciprofloxacin. Multiple antibiotic resistances were revealed against β-lactams, quinolones, and aminoglycosides families. Our overall results suggest that the obtained bacterial isolates may constitute potential candidates for bioremediation and can be useful for biotechnological applications. Genotoxic effects were assessed by a battery of biotests; the pharmaceutical wastewater was genotoxic according to the bacterial Vitotox test and micronuclei test. Genotoxicity was also evaluated by the comet test; the tail DNA damages reached 38 and 22% for concentrated sample (10×) and non-concentrated sample (1×), respectively. However, the histological sections of kidney and liver's mice treated by pharmaceutical effluent showed normal histology and no visible structural effects or alterations as cytolysis, edema, or ulcerative necrosis were observed. Residual antibiotics can reach water environment through wastewater and provoke dissemination of the antibiotics resistance and induce genotoxic effects.

Inhibitory effects of sulfamethoxazole on denitrifying granule properties: Short- and long-term tests

The broad-spectrum antibiotic sulfamethoxazole (SMX) was chosen to assess its short- and long-term effects on denitrifying granules. The SMX concentration and pre-exposure time in batch testing influenced the denitrifying granule activity. In the continuous-flow experiments, no inhibitory effects on the upflow anaerobic sludge blanket performance were observed at SMX concentrations up to 100mgL^-1, probably because of functional redundancy and long-term acclimation. The specific denitrifying activity first decreased to a minimum of 49.3% and then recovered to a level comparable to the initial level as the SMX concentration increased. The changing trend of the extracellular polymer content was consistent with the specific denitrifying activity throughout the process, and relatively high EPS loss ratios (maximum loss of 61.8%) were observed. Additionally, the diameter of the denitrifying granules monophonically increased to a final value of 35.0%. This research provided the application of denitrifying granules to treat wastewater that contained antibiotic.

Microbial population shift caused by sulfamethoxazole in engineered-Soil Aquifer Treatment (e-SAT) system

The engineered-Soil Aquifer Treatment (e-SAT) system was exploited for the biological degradation of Sulfamethoxazole (SMX) which is known to bio-accumulate in the environment. The fate of SMX in soil column was studied through laboratory simulation for a period of 90 days. About 20 ppm SMX concentration could be removed in four consecutive cycles in e-SAT. To understand the microbial community change and biological degradation of SMX in e-SAT system, metagenomic analysis was performed for the soil samples before (A-EBD) and after SMX exposure (B-EBD) in the e-SAT. Four bacterial phyla were found to be present in both the samples, with sample B-EBD showing increased abundance for Actinobacteria, Bacteroidetes, Firmicutes and decreased Proteobacterial abundance compared to A-EBD. The unclassified bacteria were found to be abundant in B-EBD compared to A-EBD. At class level, classes such as Bacilli, Negativicutes, Deltaproteobacteria, and Bacteroidia emerged in sample B-EBD owing to SMX treatment, while Burkholderiales and Nitrosomonadales appeared to be dominant at order level after SMX treatment. Furthermore, in response to SMX treatment, the family Nitrosomonadaceae appeared to be dominant. Pseudomonas was the most dominating bacterial genus in A-EBD whereas Cupriavidus dominated in sample B-EBD. Additionally, the sulfur oxidizing bacteria were enriched in the B-EBD sample, signifying efficient electron transfer and hence organic molecule degradation in the e-SAT system. Results of this study offer new insights into understanding of microbial community shift during the biodegradation of SMX.

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.

Dynamic interplay between microbial denitrification and antibiotic resistance under enhanced anoxic denitrification condition in soil

Mixed contamination of nitrate and antibiotics/antibiotic-resistant genes (ARGs) is an emerging environmental risk to farmland soil. This is the first study to explore the role of excessive anthropogenic nitrate input in the anoxic dissipation of soil antibiotic/ARGs. During the initial 10 days of incubation, the presence of soil antibiotics significantly inhibited NO₃^- dissipation, N₂O production rate, and denitrifying genes (DNGs) abundance in soil (p < 0.05). Between days 10 and 30, by contrast, enhanced denitrification clearly prompted the decline in antibiotic contents and ARG abundance. Significantly negative correlations were detected between DNGs and ARGs, suggesting that the higher the DNG activity, the more dramatic is the denitrification and the greater are the antibiotic dissipation and ARG abundance. This study provides crucial knowledge for understanding the mutual interaction between soil DNGs and ARGs in the enhanced anoxic denitrification condition.

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.

Occurrence of antibiotics in rural catchments

The transfer of 23 antibiotics from domestic and hospital sources was investigated in two elementary river watersheds receiving wastewater treatment plant (WWTP) discharges, in relation with the hydrological cycle and seasonal conditions. Antibiotic concentrations in the effluent of a WWTP treating wastewaters from both hospital and domestic sources (18-12 850 ng L^-1) were far higher than those from domestic sources exclusively (3-550 ng L^-1). In rivers, upstream of the WWTP discharges, fluoroquinolones only were found at low concentrations (≤10 ng L^-1). Their presence might be explained by transfer from contaminated agricultural fields located on the river banks. Immediately downstream of the WWTP discharge, antibiotic occurrence increased strongly with mean concentrations up to 1210 ng L^-1 for ofloxacin and 100% detection frequencies for vancomycin, sulfamethoxazole, trimethoprim and three fluoroquinolones. Dilution processes during high-flow periods led to concentrations 14 times lower than during low-flow periods. Downstream of the discharge, the antibiotic dissipation rate from the water column was higher for fluoroquinolones, in relation with their high sorption upon suspended matter and sediment. Only five antibiotics (vancomycin and four fluoroquinolones ciprofloxacin, norfloxacin, ofloxacin and enoxacin) were partly distributed (11%-36%) in the particulate phase. Downstream of the discharge, antibiotic contents in sediment ranged from 1700 to 3500 ng g^-1 dry weight, fluoroquinolones accounting for 97% of the total.

Veterinary pharmaceuticals in aqueous systems and associated effects: an update

Environmental studies have shown that pharmaceuticals can contaminate aqueous matrices, such as groundwater, surface water, sediment as well as aquatic flora and fauna. Effluents from sewage and wastewater treatment plants, pharmaceutical industries and hospitals have been implicated in such contamination. Recent studies have however revealed significant concentrations of pharmaceuticals in wastewater from animal facilities in proximal aquatic habitats. Furthermore, epidemiological studies have shown a consistent positive correlation between exposure to some drugs of veterinary importance and increased adverse effects in aquatic biota largely due to induction of endocrine disruption, antibiotic resistance, neurotoxicity, genotoxicity and oxidative stress. The aquatic habitats and associated biota are important in the maintenance of global ecosystem and food chain. For this reason, anything that compromises the integrity and functions of the aquatic environment may lead to major upset in the world's ecosystems. Therefore, knowledge about this route of exposure cannot be neglected and monitoring of their occurrence in the environment is required. This review focuses on scientific evidence that link the presence of pharmaceuticals in aqueous matrices to animal production facilities and presents means to reduce the occurrence of veterinary pharmaceutical residues in the aquatic habitats.

Fate of antibiotics from hospital and domestic sources in a sewage network

Investigation of domestic and hospital effluents in a sewage system of an elementary watershed showed that antibiotics belonging to eight classes were present with concentrations ranging from <LOQ to 50μgL^-1. The compounds most often detected in the effluents were the fluoroquinolones (79-100%), the sulfonamides (86-100%) and the macrolides (79-86%). Vancomycin, strictly reserved for hospital use in France, was detected exclusively in the hospital effluent, supporting its pertinent use as a marker of hospital discharge. Beta-lactams, which are among the most frequently consumed compounds, were rarely detected in the effluents, due to their rapid hydrolysis. Out of 23 antibiotics used in veterinary and human medicine, fourteen were quantified in both the wastewater treatment plant (WWTP) input and output: erythromycin, amoxicillin, tetracycline, trimethoprim, ormethoprim, sulfamethoxazole, vancomycin and seven quinolones (flumequine, enrofloxacin, enoxacin, ofloxacin, lomefloxacin, norfloxacin and ciprofloxacin). Antibiotic concentrations in the hospital effluent (from 0.04 to 17.9μgL^-1) were ten times higher than those measured in the domestic effluent (from 0.03 to 1.75μgL^-1), contributing to 90% of the antibiotic inputs to the WWTP. Some molecules such as sulfamethoxazole, erythromycin and trimethoprim displayed higher concentrations after wastewater treatment due to deconjugation of their metabolites, which restores the parent molecules. For other compounds, the antibiotic elimination showed discrepancies depending on their physicochemical properties. For fluoroquinolones, the apparent removal processes were mainly based on adsorption mechanisms, followed by settling, leading to sludge contamination (from 13 to 18,800μgkg^-1 dry weight).

Fate of sulfamethoxazole in groundwater: Conceptualizing and modeling metabolite formation under different redox conditions

Degradation of emerging organic compounds in saturated porous media is usually postulated as following simple low-order models. This is a strongly oversimplified, and in some cases plainly incorrect model, that does not consider the fate of the different metabolites. Furthermore, it does not account for the reversibility in the reaction observed in a few emerging organic compounds, where the parent is recovered from the metabolite. One such compound is the antibiotic sulfamethoxazole (SMX). In this paper, we first compile existing experimental data to formulate a complete model for the degradation of SMX in aquifers subject to varying redox conditions, ranging from aerobic to iron reducing. SMX degrades reversibly or irreversibly to a number of metabolites that are specific of the redox state. Reactions are in all cases biologically mediated. We then propose a mathematical model that reproduces the full fate of dissolved SMX subject to anaerobic conditions and that can be used as a first step in emerging compound degradation modeling efforts. The model presented is tested against the results of the batch experiments of Barbieri et al. (2012) and Nödler et al. (2012) displaying a non-monotonic concentration of SMX as a function of time under denitrification conditions, as well as those of Mohatt et al. (2011), under iron reducing conditions.

Effects of thiamphenicol on nitrate reduction and N2O release in estuarine and coastal sediments

Nitrate overload is an important driver of water pollution in most estuarine and coastal ecosystems, and thus nitrate reduction processes have attracted considerable attention. Antibiotics contamination is also an emerging environmental problem in estuarine and coastal regions as a result of growing production and usage of antibiotics. However, the effects of antibiotics on nitrate reduction remain unclear in these aquatic ecosystems. In this study, continuous-flow experiments were conducted to examine the effects of thiamphenicol (TAP, a common chloramphenicol antibiotic) on nitrate reduction and greenhouse gas N2O release. Functional genes involved in nitrogen transformation were also quantified to explore the microbial mechanisms of the TAP influence. Production of N2 were observed to be inhibited by TAP treatment, which implied the inhibition effect of TAP on nitrate reduction processes. As intermediate products of nitrogen transformation processes, nitrite and N2O were observed to accumulate during the incubation. Different TAP inhibition effects on related functional genes may be the microbial mechanism for the changes of nutrient fluxes, N2 fluxes and N2O release rates. These results indicate that the antibiotics residues in estuarine and coastal ecosystems may contribute to nitrate retention and N2O release, which could be a major factor responsible for eutrophication and greenhouse effects.

Occurrence of antibiotics in pharmaceutical industrial wastewater, wastewater treatment plant and sea waters in Tunisia

Antibiotics are among the most commonly used group of pharmaceuticals in human medicine. They can therefore reach surface and groundwater bodies through different routes, such as wastewater treatment plant effluents, surface runoff, or infiltration of water used for agricultural purposes. It is well known that antibiotics pose a significant risk to environmental and human health, even at low concentrations. The aim of the present study was to evaluate the presence of aminoglycosides and phenicol antibiotics in municipal wastewaters, sea water and pharmaceutical effluents in Tunisia. All analysed water samples contained detectable levels of aminoglycoside and phenicol antibiotics. The highest concentrations in wastewater influents were observed for neomycin and kanamycin B (16.4 ng mL(-1) and 7.5 ng mL(-1), respectively). Chloramphenicol was found in wastewater influents up to 3 ng mL(-1). It was observed that the waste water treatment plants were not efficient in completely removing these antibiotics. Chloramphenicol and florfenicol were found in sea water samples near aquaculture sites at levels up to, respectively, 15.6 ng mL(-1) and 18.4 ng mL(-1). Also aminoglycoside antibiotics were found near aquaculture sites with the highest concentration of 3.4 ng mL(-1) for streptomycin. In pharmaceutical effluents, only gentamycin was found at concentrations up to 19 ng mL(-1) over a sampling period of four months.

Do antibiotics have environmental side-effects? Impact of synthetic antibiotics on biogeochemical processes

Antibiotic use in the early 1900 vastly improved human health but at the same time started an arms race of antibiotic resistance. The widespread use of antibiotics has resulted in ubiquitous trace concentrations of many antibiotics in most environments. Little is known about the impact of these antibiotics on microbial processes or "non-target" organisms. This mini-review summarizes our knowledge of the effect of synthetically produced antibiotics on microorganisms involved in biogeochemical cycling. We found only 31 articles that dealt with the effects of antibiotics on such processes in soil, sediment, or freshwater. We compare the processes, antibiotics, concentration range, source, environment, and experimental approach of these studies. Examining the effects of antibiotics on biogeochemical processes should involve environmentally relevant concentrations (instead of therapeutic), chronic exposure (versus acute), and monitoring of the administered antibiotics. Furthermore, the lack of standardized tests hinders generalizations regarding the effects of antibiotics on biogeochemical processes. We investigated the effects of antibiotics on biogeochemical N cycling, specifically nitrification, denitrification, and anammox. We found that environmentally relevant concentrations of fluoroquinolones and sulfonamides could partially inhibit denitrification. So far, the only documented effects of antibiotic inhibitions were at therapeutic doses on anammox activities. The most studied and inhibited was nitrification (25-100 %) mainly at therapeutic doses and rarely environmentally relevant. We recommend that firm conclusions regarding inhibition of antibiotics at environmentally relevant concentrations remain difficult due to the lack of studies testing low concentrations at chronic exposure. There is thus a need to test the effects of these environmental concentrations on biogeochemical processes to further establish the possible effects on ecosystem functioning.

Exposure to vancomycin causes a shift in the microbial community structure without affecting nitrate reduction rates in river sediments

Antibiotics and antibiotic resistance genes have shown to be omnipresent in the environment. In this study, we investigated the effect of vancomycin (VA) on denitrifying bacteria in river sediments of a Waste Water Treatment Plant, receiving both domestic and hospital waste. We exposed these sediments continuously in flow-through reactors to different VA concentrations under denitrifying conditions (nitrate addition and anoxia) in order to determine potential nitrate reduction rates and changes in sedimentary microbial community structures. The presence of VA had no effect on sedimentary nitrate reduction rates at environmental concentrations, whereas a change in bacterial (16S rDNA) and denitrifying (nosZ) community structures was observed (determined by polymerase chain reaction-denaturing gradient gel electrophoresis). The bacterial and denitrifying community structure within the sediment changed upon VA exposure indicating a selection of a non-susceptible VA population.

Adaption of the microbial community to continuous exposures of multiple residual antibiotics in sediments from a salt-water aquacultural farm

Residual antibiotics from aquacultural farming may alter microbial community structure in aquatic environments in ways that may adversely or positively impact microbially-mediated ecological functions. This study investigated 26 ponds (26 composited samples) used to produce fish, razor clam and shrimp (farming and drying) and 2 channels (10 samples) in a saltwater aquacultural farm in southern China to characterize microbial community structure (represented by phospholipid fatty acids) in surface sediments (0-10 cm) with long-term exposure to residual antibiotics. 11 out of 14 widely-used antibiotics were quantifiable at μg kg(-1) levels in sediments but their concentrations did not statistically differ among ponds and channels, except norfloxacin in drying shrimp ponds and thiamphenicol in razor clam ponds. Concentrations of protozoan PLFAs were significantly increased in sediments from razor clam ponds while other microbial groups were similar among ponds and channels. Both canonical-correlation and stepwise-multiple-regression analyses on microbial community and residual antibiotics suggested that roxithromycin residuals were significantly related to shifts in microbial community structure in sediments. This study provided field evidence that multiple residual antibiotics at low environmental levels from aquacultural farming do not produce fundamental shifts in microbial community structure.

Probabilistic risk assessment of veterinary medicines applied to four major aquaculture species produced in Asia

Aquaculture production constitutes one of the main sources of pollution with veterinary medicines into the environment. About 90% of the global aquaculture production is produced in Asia and the potential environmental risks associated with the use of veterinary medicines in Asian aquaculture have not yet been properly evaluated. In this study we performed a probabilistic risk assessment for eight different aquaculture production scenarios in Asia by combining up-to-date information on the use of veterinary medicines and aquaculture production characteristics. The ERA-AQUA model was used to perform mass balances of veterinary medicinal treatments applied to aquaculture ponds and to characterize risks for primary producers, invertebrates, and fish potentially exposed to chemical residues through aquaculture effluents. The mass balance calculations showed that, on average, about 25% of the applied drug mass to aquaculture ponds is released into the environment, although this percentage varies with the chemical's properties, the mode of application, the cultured species density, and the water exchange rates in the aquaculture pond scenario. In general, the highest potential environmental risks were calculated for parasitic treatments, followed by disinfection and antibiotic treatments. Pangasius catfish production in Vietnam, followed by shrimp production in China, constitute possible hot-spots for environmental pollution due to the intensity of the aquaculture production and considerable discharge of toxic chemical residues into surrounding aquatic ecosystems. A risk-based ranking of compounds is provided for each of the evaluated scenarios, which offers crucial information for conducting further chemical and biological field and laboratory monitoring research. In addition, we discuss general knowledge gaps and research priorities for performing refined risk assessments of aquaculture medicines in the near future.

Chronic exposure of river sediments to environmentally relevant levels of tetracycline affects bacterial communities but not denitrification rates

The effects of tetracycline (TC) at chronic sub-inhibitory exposure concentrations on benthic denitrification rates and bacterial communities were explored. River sediments were continuously exposed to different TC concentrations (0.5, 20 and 10,000 μg L(-1)) for 2 weeks in flow-through reactors allowing denitrification and bacterial growth conditions. Bacterial communities were fingerprinted by Denaturing Gradient Gel Electrophoresis of 16S rRNA gene amplification products. Cultivable denitrifiers enriched from the sediment were tested for TC resistance (2-128 mg L(-1)). Denitrification rates were unaffected by exposure to TC, regardless of concentration. In contrast, the bacterial community composition changed significantly from sub-inhibitory (ng-μg L(-1)) to therapeutic (mg L(-1)) exposure concentrations. Furthermore the cultivable denitrifiers showed a high TC sensitivity (<4 mg L(-1)). Maintenance of efficient benthic denitrification rates, even at the highest level of TC exposure most likely originated from an adaptation of the autochthonous bacterial community where dominant species become those that acquire, or already have resistance to antibiotics.