Identification of functional microflora underlying the biodegradation of sulfadiazine-contaminated substrates by Hermetia illucens.

The increasing discharge of antibiotic residues into the natural environment, stemming from both human activities and animal farming, has detrimental effects on natural ecosystems and serves as a significant driving force for the spread of antibiotic resistance. Biodegradation is an important method for the elimination of antibiotics from contaminated substrates, but the identifying in situ microbial populations involved in antibiotic degradation is challenging. Here, DNA stable isotope probing (DNA-SIP) was employed to identify active sulfadiazine (SDZ) degrading microbes in the gut of black soldier fly larvae (BSFLs). At an initial SDZ concentration of 100 mg kg-1, the highest degradation efficiency reached 73.99% after 6 days at 28 °C. DNA-SIP revealed the incorporation of 13C6 from labeled SDZ in 9 genera, namely, Clostridum sensu stricto 1, Nesterenkonia, Bacillus, Halomonas, Dysgonomonas, Caldalkalibacillus, Enterococcus, g_unclassified_f_Xanthomonadaceae and g_unclassified_f_Micrococcaceae. Co-occurrence network analysis revealed that a significant positive correlation existed among SDZ degrading microbes in the gut microbiota, e.g., between Clostridium sensu stricto 1 and Nesterenkonia. Significant increases in carbohydrate metabolism, membrane transport and translation were crucial in the biodegradation of SDZ in the BSFL gut. These results elucidate the structure of SDZ-degrading microbial communities in the BSFL gut and in situ degradation mechanisms.

Interactions between sulfonamide homologues and glycosyltransferase induced metabolic disorders in rice (Oryza sativa L.).

Sulfadiazine and its derivatives (sulfonamides, SAs) could induce distinct biotoxic, metabolic and physiological abnormalities, potentially due to their subtle structural differences. This study conducted an in-depth investigation on the interactions between SA homologues, i.e. sulfadiazine (SD), sulfamerazine (SD1), and sulfamethazine (SD2), and the key metabolic enzyme (glycosyltransferase, GT) in rice (Oryza sativa L.). Untargeted screening of SA metabolites revealed that GT-catalyzed glycosylation was the primary transformation pathway of SAs in rice. Molecular docking identified that the binding sites of SAs on GT (D0TZD6) were responsible for transferring sugar moiety to synthesize polysaccharides and detoxify SAs. Specifically, amino acids in the GT-binding cavity (e.g., GLY487 and CYS486) formed stable hydrogen bonds with SAs (e.g., the sulfonamide group of SD). Molecular dynamics simulations revealed that SAs induced conformational changes in GT ligand binding domain, which was supported by the significantly decreased GT activity and gene expression level. As evidenced by proteomics and metabolomics, SAs inhibited the transfer and synthesis of sugar but stimulated sugar decomposition in rice leaves, leading to the accumulation of mono- and disaccharides in rice leaves. While the differences in the increased sugar content by SD (24.3%, compared with control), SD1 (11.1%), and SD2 (6.24%) can be attributed to their number of methyl groups (0, 1, 2, respectively), which determined the steric hindrance and hydrogen bonds formation with GT. This study suggested that the disturbances on crop sugar metabolism by homologues contaminants are determined by the interaction between the contaminants and the target enzyme, and are greatly dependent on the steric hindrance effects contributed by their side chains. The results are of importance to identify priority pollutants and ensure crop quality in contaminated fields.

Understanding the cometabolic degradation of sulfadiazine by an enriched ammonia oxidizing bacteria culture from both extracellular and intracellular perspectives.

Antibiotics are widely used drugs in the world and pose serious threats to ecosystems and human health. Although it has been reported that ammonia oxidizing bacteria (AOB) can cometabolize antibiotics, little has been reported on how AOB would respond to the exposure of antibiotics on extracellular and enzymatic levels, as well as the impact of antibiotics on the bioactivity of AOB. Therefore, in this study, a typical antibiotic, sulfadiazine (SDZ), was selected, and a series short-term batch tests using enriched AOB sludge were conducted to investigate the intracellular and extracellular responses of AOB along the cometabolic degradation process of SDZ. The results showed the cometabolic degradation of AOB made the main contribution to SDZ removal. When the enriched AOB sludge was exposed to SDZ, ammonium oxidation rate, ammonia monooxygenase activity, adenosine triphosphate concentration and dehydrogenases activity were negatively affected. The amoA gene abundance increased 1.5 folds within 24 h, which may enhance the uptake and utilization of substrates and maintain stable metabolic activity. In the tests with and without ammonium, the concentration of total EPS increased from 264.9 to 231.1 mg/gVSS to 607.7 and 538.2 mg/gVSS, respectively, under the exposure to SDZ, which was mainly contributed by the increase of proteins in tightly bound extracellular polymeric substances (EPS) and polysacharides in tightly bound EPS and soluble microbial products. The proportion of tryptophan-like protein and humic acid-like organics in EPS also increased. Moreover, SDZ stress stimulated the secretion of three quorum sensing signal molecules, C4-HSL (from 140.3 to 164.9 ng/L), 3OC6-HSL (from 17.8 to 42.4 ng/L) and C8-HSL (from 35.8 to 95.9 ng/L) in the enriched AOB sludge. Among them, C8-HSL may be a key signal molecule that promoted the secretion of EPS. The findings of this study could shed more light on the cometabolic degradation of antibiotics by AOB.

Joint toxicity mechanisms of perfluorooctanoic acid and sulfadiazine on submerged macrophytes and periphytic biofilms.

Hazardous chemicals, such as perfluoroalkyl substances (PFASs) and antibiotics, coexist in aquatic environments and pose a severe threat to aquatic organisms. However, research into the toxicity of these pollutants on submerged macrophytes and their periphyton is still limited. To assess their combined toxicity, Vallisneria natans (V. natans) was exposed to perfluorooctanoic acid (PFOA) and sulfadiazine (SD) at environmental concentrations. Photosynthetic parameters such as chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids were lower in the SD exposure group, indicating that SD had a significant effect on the photosynthesis of aquatic plants. Single and combined exposures effectively induced antioxidant responses, with increases in superoxide dismutase, peroxidase activities, and ribulose-1,5-bisphosphate carboxylase concentrations, as well as malondialdehyde content. Accordingly, antagonistic toxicity was assessed between PFOA and SD. Furthermore, metabolomics revealed that V. natans improved stress tolerance through changes in enoic acid, palmitic acid, and palmitoleoyloxymyristic acid related to the fatty acid metabolism pathway responding to the coexisting pollutants. Additionally, PFOA and SD in combination induced more effects on the microbial community of biofilm. The alternation of α- and ß-D-glucopyranose polysaccharides and the increased content of autoinducer peptides and N-acylated homoserine lactones indicated that PFOA and SD changed the structure and function of biofilm. These investigations provide a broader perspective and comprehensive analysis of the responses of aquatic plants and periphyton biofilms to PFAS and antibiotics in the environment.

Effect of antibiotic and/or heavy metal on nitrogen cycle of sediment-water interface in aquaculture system: Implications from sea cucumber culture.

Antibiotics and heavy metals can have a negative impact on the nitrogen (N) cycle and microbial metabolism in coastal aquaculture environment. An indoor simulated culture experiment was conducted to explore how sulfadiazine and lead influence the N cycling in aquatic environment. Specifically, the experiment involved adding sulfadiazine (SDZ), lead (Pb), a combination of SDZ and Pb (SP), and a control group (CK). The fluxes and contents of ammonia nitrogen (NH4+-N), nitrate nitrogen (NO3--N) and nitrite nitrogen (NO2--N) in sediment-water interface and sediments, the abundance of N cycle function genes (amoA_AOB, hzsA, nar, nirK, nirS, norB and nosZ) and microbiota in sediments were analyzed. The results showed that the presence of SDZ and Pb inhibited the nitrification function gene and nitrifiers abundance in surface sediment, and thus leading to more accumulation of NH4+ and NO2- in overlying water. Pb exposure increased the abundances of denitrifying bacteria stimulated the first three steps of denitrification in the sediment, resulting in more removal of NO3- from the sediment, but possibly had the risk of releasing more greenhouse gas N2O. Conversely, the presence of SDZ ultimately inhibited denitrification and anammox bacterial activities in the sediment. This study revealed how heavy metal and antibiotic impair the microbial communities and N cycling function gene expression, leading to the deterioration of typical coastal aquaculture environments.

The different toxicological effects and removal efficiencies of norfloxacin and sulfadiazine in culturing Arthrospira (Spirulina) platensis.

Norfloxacin (NFX) and sulfadiazine (SDZ) are two widely used antibiotics belonging to fluoroquinolone and sulfonamide groups, respectively, and have become the commonly detected micropollutants in aquatic environments. However, only few works have been conducted to investigate the highly probable inhibition of these antibiotic pollutants to Arthrospira platensis, which is an important species of cyanobacteria that is one of primary producers in aquatic ecosystems and should be remarkably sensitive to environmental pollutants due to its prokaryotic characteristics. Hence, the toxicological effects and removal efficiencies of NFX and SDZ in culturing A. platensis were studied by analyzing the biomass growth, photosynthetic pigments, primary biocomponents, and antibiotics concentration. The corresponding variations of these characteristics showed the higher sensitivity of A. platensis to NFX than to SDZ, indicating the specifically targeted effect of NFX on A. platensis, which could be confirmed in silico by the higher binding affinity of NFX with the critical enzyme. The obtained results illustrated the roles of NFX and SDZ on the growth of A. platensis, thus providing the great support in employing A. platensis to reduce hazards from contaminated water and recover biomass resources.

Periodic mesoporous organosilicas containing naphthalenediimides as organic sensitizers for sulfadiazine photodegradation.

In this work, periodic mesoporous organosilicas (PMO) functionalized with the organic sentisizer naphthalenediimide (NDI) were employed as heterogeneous catalysts for the photodegradation of the antibiotic sulfadiazine (SDZ), taken as a model for contaminants of emerging concern (CECs). The catalysts, designated as PMONDI, were prepared by surfactant-directed co-condensation of the precursor N,N'-bis(3-triethoxysilylpropyl)- 1,4,5,8-naphthalenediimide with tetraethoxysilane. The synthesized PMONDI were characterized using transmission electron microscopy, nitrogen adsorption isotherms and small and large angle x-ray scattering. The performance of PMONDI catalysts in the photodegradation of SDZ was compared to that of TiO2 nanoparticles impregnated into SBA-15 mesoporous silica (TiO2/SBA-15), under irradiation with a Hg lamp with a bandpass filter of 320-500 nm. Under optimal conditions, PMONDI degraded 100% of the SDZ in 45 min, while the total degradation of SDZ was achieved only after 150 min with TiO2/SBA-15. PMONDI also performed better than TiO2/SBA-15 in reuse tests. The mechanism of photodegradation with PMONDI involves the formation of excited triplet states of NDI (3NDI*) upon irradiation, which can then react with molecular oxygen to form reactive oxygen species, which degrade SDZ. Analysis of the SDZ degradation products indicated two main pathways: (1) hydroxylation of the aniline ring and (2) SO2 extrusion and rearrangement, followed by oxidation of the aniline ring to nitrobenzene. In conclusion, the great potential of the PMONDI materials as photocatalysts for CECs degradation was demonstrated in this work, encouraging further research on these materials for the degradation of pollutants.

Antibiotic sulfadiazine degradation by persulfate oxidation: Intermediates dependence of ecotoxicity and the induction of antibiotic resistance genes.

To preserve the water resources, this study has analyzed the ecotoxicity and antibiotic resistance genes (ARGs) induction capacity of sulfadiazine degradation intermediates resulting from persulfate activation oxidation enhanced by ultraviolet, ultrasound and microwave. The five degradation pathways caused by the contribution discrepancy of electron transfer and singlet oxygen (1O2) and variations in the ecotoxicity of different degradation products were analyzed. Microcosm experiment exhibited that the microbial community in actual water changed significantly with SDZ and degradation intermediates, in which the dominant genera were Aeromonas, Cupriavidus, Elizabethkingia and Achromobacter. Except for the selective pressure on bacteria, the degradation intermediates also exert a certain degree or even stronger induction on sulfonamide ARGs (sul4, sul1 and sul2) than SDZ. Furthermore, the potential hosts for sulfonamide ARGs were revealed by network analysis. These results provide a better understanding of antibiotics degradation mechanism and ARGs occurrence, which is useful for controlling the spread of ARGs.

Pyrimidine salvage in Toxoplasma gondii as a target for new treatment.

Toxoplasmosis is a common protozoan infection that can have severe outcomes in the immunocompromised and during pregnancy, but treatment options are limited. Recently, nucleotide metabolism has received much attention as a target for new antiprotozoal agents and here we focus on pyrimidine salvage by Toxoplasma gondii as a drug target. Whereas uptake of [3H]-cytidine and particularly [3H]-thymidine was at most marginal, [3H]-uracil and [3H]-uridine were readily taken up. Kinetic analysis of uridine uptake was consistent with a single transporter with a Km of 3.3 ± 0.8 µM, which was inhibited by uracil with high affinity (Ki = 1.15 ± 0.07 µM) but not by thymidine or 5-methyluridine, showing that the 5-Me group is incompatible with uptake by T. gondii. Conversely, [3H]-uracil transport displayed a Km of 2.05 ± 0.40 µM, not significantly different from the uracil Ki on uridine transport, and was inhibited by uridine with a Ki of 2.44 ± 0.59 µM, also not significantly different from the experimental uridine Km. The reciprocal, complete inhibition, displaying Hill slopes of approximately -1, strongly suggest that uridine and uracil share a single transporter with similarly high affinity for both, and we designate it uridine/uracil transporter 1 (TgUUT1). While TgUUT1 excludes 5-methyl substitutions, the smaller 5F substitution was tolerated, as 5F-uracil inhibited uptake of [3H]-uracil with a Ki of 6.80 ± 2.12 µM (P > 0.05 compared to uracil Km). Indeed, we found that 5F-Uridine, 5F-uracil and 5F,2'-deoxyuridine were all potent antimetabolites against T. gondii with EC50 values well below that of the current first line treatment, sulfadiazine. In vivo evaluation also showed that 5F-uracil and 5F,2'-deoxyuridine were similarly effective as sulfadiazine against acute toxoplasmosis. Our preliminary conclusion is that TgUUT1 mediates potential new anti-toxoplasmosis drugs with activity superior to the current treatment.

Human MHC class I molecule, HLA-A2.1, mediates activation of CD8+ T cell IFN-γ production and the T cell-dependent protection against reactivation of cerebral Toxoplasma infection.

To examine whether the HLA-A2.1, one of the most common MHC class I molecules in humans, activates the protective immunity against reactivation of cerebral infection with Toxoplasma gondii, HLA-A2.1-transgenic and wild-type (WT) mice were infected and treated with sulfadiazine to establish chronic infection in their brains. One month after discontinuation of sulfadiazine, which initiates reactivation of the infection, mRNA levels for tachyzoite (the acute stage form)-specific SAG1 and numbers of the foci associated tachyzoites were significantly less in the brains of the HLA-A2.1-transgenic than WT mice. Greater numbers of IFN-γ-producing CD8+ T cells were detected in the spleens of infected transgenic than WT mice, and CD8+ T cells from the former produced markedly greater amounts of IFN-γ than the T cells from the latter in response to tachyzoite antigens in vitro. When their CD8+ T cells were systemically transferred to infected immunodeficient NSG mice expressing the HLA-A2.1, the CD8+ T cells from HLA-A2.1-transgenic mice inhibited reactivation of the cerebral infection in the recipients more efficiently than did the WT T cells. Furthermore, the inhibition of reactivation of the infection by CD8+ T cells from the transgenic mice was associated with increased cerebral expression of IFN-γ and effector molecules against tachyzoites in the recipients when compared to the WT CD8+ T cell recipients. Thus, the human HLA-A2.1 is able to effectively activate IFN-γ production of CD8+ T cells against T. gondii tachyzoites and confer a potent protection against reactivation of cerebral infection with this parasite through the CD8+ T cells activation.

The antibacterials ciprofloxacin, trimethoprim and sulfadiazine modulate gene expression, biomarkers and metabolites associated with stress and growth in gilthead sea bream (Sparus aurata).

The high consumption and subsequent input of antibacterial compounds in marine ecosystems has become a worldwide problem. Their continuous presence in these ecosystems allows a direct interaction with aquatic organisms and can cause negative effects over time. The objective of the present study was to evaluate the effects of exposure to three antibacterial compounds of high consumption and presence in marine ecosystems (Ciprofloxacin CIP, Sulfadiazine SULF and Trimethoprim TRIM) on the physiology of the gilthead sea bream, Sparus aurata. Plasma parameters, enzymatic biomarkers of oxidative stress and damage and expression of genes related to stress and growth were assessed in exposed S. aurata specimens. For this purpose, sea bream specimens were exposed to individual compounds at concentrations of 5.2 ± 2.1 µg L-1 for CIP, 3.8 ± 2.7 µg L-1 for SULF and 25.7 ± 10.8 µg L-1 for TRIM during 21 days. Exposure to CIP up-regulated transcription of genes associated with the hypothalamic-pituitary-thyroid (HPT) (thyrotropin-releasing hormone, trh) and hypothalamic-pituitary-interrenal (HPI) axes (corticotropin-releasing hormone-binding protein, crhbp) in the brain, as well as altering several hepatic stress biomarkers (catalase, CAT; glutathione reductase, GR; and lipid peroxidation, LPO). Similar alterations at the hepatic level were observed after exposure to TRIM. Overall, our study indicates that S. aurata is vulnerable to environmentally relevant concentrations of CIP and TRIM and that their exposure could lead to a stress situation, altering the activity of antioxidant defense mechanisms as well as the activity of HPT and HPI axes.

Enhanced sulfonamides removal via microalgae-bacteria consortium via co-substrate supplementation.

Both co-cultivation and co-substrate addition strategies have exhibited massive potential in microalgae-based antibiotic bioremediation. In this study, glucose and sodium acetate were employed as co-substrate in the cultivation of microalgae-bacteria consortium for enhanced sulfadiazine (SDZ) and sulfamethoxazole (SMX) removal. Glucose demonstrated a two-fold increase in biomass production with a maximum specific growth rate of 0.63 ± 0.01 d-1 compared with sodium acetate. The supplementation of co-substrate enhanced the degradation of SDZ significantly up to 703 ± 18% for sodium acetate and 290 ± 22% for glucose, but had almost no effect on SMX. The activities of antioxidant enzymes, including peroxidase, superoxide dismutase and catalase decreased with co-substrate supplementation. Chlorophyll a was associated with protection against sulfonamides and chlorophyll b might contribute to SDZ degradation. The addition of co-substrates influenced bacterial community structure greatly. Glucose enhanced the relative abundance of Proteobacteria, while sodium acetate improved the relative abundance of Bacteroidetes significantly.

Mechanism, electrochemistry and biotoxicity analysis of the biodegradation of sulfadiazine on Nickel(â ¡)/Manganese(â ¡)-modified graphite felt bioanode.

Sulfadiazine (SDZ) is one of the most representative sulfonamides antibiotics, and its biodegradation has become a research hotspot in recent years. The present study innovatively adopted a microbial fuel cells with a Nickel (Ⅱ) and Manganese (Ⅱ)-decorated graphite felt bioanode (Ni(Ⅱ)/Mn (Ⅱ)-MFCs) to remove SDZ. The results demonstrated that the Ni(Ⅱ)/Mn (Ⅱ)-MFCs exhibited improved electrochemical performance, with a higher power density (742.98 ± 58.33 mW/m2) compared to the control MFCs (678.34 ± 52.87 mW/m2), an overall lower anode potential, and a larger double layer area (cyclic voltammetry). After 5 months of operation, approximately 97.95% of 30 mg/L SDZ was degraded within 120 h, which was 11.46% higher than that of the control MFCs. Moreover, SDZ and its byproducts could be better mineralized in the Ni(Ⅱ)/Mn (Ⅱ)-MFCs than the control, and the biotoxicity of SDZ towards Escherichia coli and Vibro qinghaiensis sp. Q67 could be greatly decreased after treatment with the modified MFCs. Based on the metabolites, we hypothesized that the chemical reactions hydroxylation, ammoxidation, SO2-extrusion, sulfur-reduction, etc. played a significant role in SDZ biodegradation. A microbial community analysis revealed that Dechloromonas (2.37%), Denitratisoma (5.32%) and Lentimicrobium (26.35%) were the dominant functional microbes in the Ni(Ⅱ)/Mn (Ⅱ)-MFCs. This study may provide insights and a theoretical basis for the biodegradation of sulfonamides and thus may facilitate further investigations and relevant findings.

Efficient elimination of sulfadiazine in an anaerobic denitrifying circumstance: Biodegradation characteristics, biotoxicity removal and microbial community analysis.

Sulfadiazine (SDZ) is widely used in clinical treatment, livestock husbandry and aquaculture as an antibacterial agent, resulting in environmental risks. In this work, batch experiments were conducted to investigate the characteristics of SDZ biodegradation and reaction mechanisms in a nitrate anaerobic denitrifying system for the first time. The results showed that 98.52% of the SDZ, which had an initial concentration of 50 mg L-1, was degraded after 70 h, indicating that the removal efficiency of SDZ in anaerobic denitrifying system was 55.27% higher than that in anaerobic system. Furthermore, LC-MS-MS analysis confirmed that SDZ could be degraded into 16 byproducts via 3 main degradation pathways that contained 6 different reactions. After analyzing the microbial communities of the reactor, the denitrifying bacteria and desulfurizing bacteria Desulforhabdus, Ignavibacterium, SBR1031_norank, Nocardioides, etc. were highly associated with the removal of SDZ in the system. The biological toxicity test of the effluent indicated that the remaining organic matter and inorganic matter of the effluent could provide nutrients for E. coli and promote its growth. In other words, anaerobic denitrifying systems are highly efficient, simple and environmentally friendly, and have an impressive prospect in the biodegradation of sulfonamide antibiotics.

Efficient sulfadiazine degradation via in-situ epitaxial grow of Graphitic Carbon Nitride (g-C3N4) on carbon dots heterostructures under visible light irradiation: Synthesis, mechanisms and toxicity evaluation.

The synthesis of environmental-friendly metal-free photocatalysts has great significance in photocatalytic technology. In this work, we firstly report the successful synthesis of in situ epitaxial growth of g-C3N4 on carbon dots through a facile thermal polymerization technique. Characterization and density functional theory (DFT) calculations were conducted to clarify the structure engineering and the electronic/chemical properties of the in-plane interconnected carbon dots/g-C3N4 (C-CN) heterostructures. With the optimal carbon dots content, the C-CN exhibited 3.2 times higher degradation rate for sulfadiazine (SDZ) than that of g-C3N4. Besides, the C-CN heterostructures displayed excellent stability and reusability in five consecutive cycles. The enhanced photocatalytic activity was related to the narrowed band gap and the local electronic density of valance band and conduction band orbitals of the unique plane heterostructures, corroborated by the spectroscopic characterizations and theoretical calculations. Photogenerated holes dominated the degradation of SDZ, while OH showed a negligible contribution. Moreover, DFT calculation succeeded to predict that the atoms with high Fukin index (f0) on SDZ molecule were more vulnerable to radicals attack. SDZ degradation pathway mainly included smiles-type rearrangement, SO2 extrusion, ring hydroxylation and SN bond cleavage processes. The eco-toxicity assessment revealed the generation of less toxic intermediates after photocatalysis. Our findings not only afford a new technique for constructing g-C3N4-based in-plane heterostructures with high and stable photocatalytic efficiency, but also highlight the feasible application of metal-free photocatalysts in environmental remediation.

Microbial Transformation of A Sulfonamide Antibiotic Under Various Background Nutrient Conditions.

Certain microbes can biotransform antibiotics. Little is known about these microbes or the biotransformation processes. The objective of this study was to determine the effects of background nutrient conditions on a sulfonamide degrading culture and on its biotransformation of sulfadiazine (SDZ) with respect to transformation kinetics and transformation products. The mixed culture capable of degrading SDZ consisted primarily of three genera, Brevibacterium, Castellaniella and Leucobacter. The maximum biotransformation rate was 4.55 mg L-1 d-1 in the absence of background nutrients. Among the three background nutrient conditions tested, diluted R2A medium lead to the highest maximum SDZ biotransformation rates, followed by humic acid and glucose. 2-aminopyrimidine was the major SDZ biotransformation product under the background nutrient conditions tested, while another previously reported biotransformation product, sulfanilic acid, was further degraded by the mixed culture. The findings from this study can help improve our estimation of the fate of antibiotics in the environment.

Insight into the nitrification kinetics and microbial response of an enriched nitrifying sludge in the biodegradation of sulfadiazine.

The intensive use of antibiotics results in the continuous release of antibiotics into wastewater treatment systems, leading to the spread of antibiotic resistance. Nitrifying system is reported to be capable of degrading antibiotics, yet few studies have systematically investigated the inherent correlation among ammonium oxidation rate, antibiotic degradation and genetic expression of nitrifying bacteria along the process. This study selected a widely used sulfonamide antibiotic, sulfadiazine (SDZ), to investigate its biodegradation potential by an enriched nitrifying culture and the response of nitrifying bacteria against antibiotic exposure. Our results demonstrated that SDZ degradation was mainly contributed by cometabolism of ammonia-oxidizing bacteria (AOB), rather than biomass adsorption. The quantitative reverse transcription PCR (RT-qPCR) analysis revealed that the expression level of amoA gene was down-regulated due to the SDZ exposure. In addition, the degradation products of SDZ did not exhibit inhibitory effect on Escherichia coli K12, indicating the biotoxicity of SDZ could be mitigated after biodegradation. The findings offer insights regarding the biodegradation process of sulfonamide antibiotics via cometabolism by AOB.

Sulfadiazine degradation in soils: Dynamics, functional gene, antibiotic resistance genes and microbial community.

Sulfonamides and their corresponding antibiotic resistance genes (ARGs) are widespread in the environment, which leads to a major threat to global health crisis. Biodegradation plays a major role in sulfonamides removal in soil ecosystem, but the degradation dynamics and the associated functional bacteria in situ remain unclear. In this study, aerobic degradation of sulfadiazine (SDZ) at two dosages (1 and 10 mg/kg) was explored for up to 70 days in two different agricultural soils. The removal of SDZ in all treatments followed first-order multi-compartment model with half-life times of 0.96-2.57 days, and DT50 prolonged with the increase of initial dosage. A total of seven bacterial genera, namely Gaiella, Clostrium_sensu_stricto_1, Tumebacillus, Roseiflexus, Variocorax, Nocardioide and Bacillus, were proposed as the potential SDZ-degraders. sadA gene was for the first time detected in soil samples, but other functional genes might also participate in SDZ degradation. The enrichment of sulfonamide resistance genes was found after 70 days' incubation, which might result in the spread of ARGs in soil. This study can add some new insights towards SDZ degradation in soil ecosystem and provide a potential resource for the bioremediation of SDZ-contaminated soil.

Sulfadiazine biodegradation by Phanerochaete chrysosporium: Mechanism and degradation product identification.

Antibiotic contaminants have become a severe environmental problem in recent years and finding effective ways to deal with this issue is of great importance. In this study, Phanerochaete chrysosporium was used to degrade sulfadiazine (SDZ), which is frequently detected in the culture medium of isolates from soil and surface water systems. The results demonstrate that 10 mg L-1 SDZ can be completely degraded by P. chrysosporium under conditions of pH 5.7 and 30 °C within 6 days. The Q-Exactive-MS/MS analysis identified and confirmed several different SDZ degradation intermediates, and four proposed degradation pathways of SDZ were deduced. Moreover, enzyme activity tests revealed that manganese peroxidase and ligninolytic peroxidase played important roles in SDZ degradation. Moreover, a transcriptome analysis method was performed to explore the mechanism and pathways of SDZ degradation by P. chrysosporium in greater detail. The results of GO and KEGG analysis strongly suggest that the metabolism pathway is significantly activated and plays an important role in antibiotic degradation. Further, this is the first study to identify SDZ degradation intermediates and two main intermediates were found to be involved in possible SDZ degradation pathways. This study is also the first report results from RNA sequencing to evaluate genome-wide changes of P. chrysosporium to further explore SDZ degradation mechanism.

Effects and Removal of the Antibiotic Sulfadiazine by Eichhornia crassipes: Potential Use for Phytoremediation.

The antibiotic sulfadiazine (SDZ) is a challenging threat to the health of aquatic organisms, as it frequently occurs in aquatic ecosystems. Tolerance mechanisms and accumulation of SDZ in a floating macrophyte (Eichhornia crassipes) under hydroponic conditions were investigated in this study to provide more insight into the SDZ removal process. Results show that the presence of 1 mg L-1 SDZ decreased the quickest and ranged from 669.45 to 165.34 µg L-1 from days 5 to 25. Exposing E. crassipes to SDZ ( < 1 mg L-1) maintained stable leaf photosynthetic efficiency. The overall increase in superoxide dismutase and peroxidase activities with SDZ treatments indicated that leaves were resistant. SDZ was absorbed by E. crassipes, following the sequence of root > aerial parts under all treatments. These findings suggest that E. crassipes has the ability to phytoremediation SDZ contaminated water.