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

Ammonia monooxygenase-mediated cometabolic biotransformation of volatile 4-chlorophenol in nitrifying counter-diffused biofilms: A combined molecular dynamics simulation, DFT calculation and experimental study

Ammonia monooxygenase (AMO)-mediated cometabolism of organic pollutants has been widely observed in biological nitrogen removal process. However, its molecular mechanism remains unclear, hindering its practical application. Furthermore, conventional nitrification systems encounter significant challenges such as air pollution and the loss of ammonia-oxidizing bacteria, when dealing with wastewater containing volatile organic pollutants. This study developed a nitrifying membrane-aerated biofilm reactor (MABR) to enhance the biodegradation of volatile 4-chlorophenol (4-CP). Results showed that 4-CP was primarily removed via Nitrosomonas nitrosa-mediated cometabolism in the presence of NH4+-N, supported by the increased nicotinamide adenine dinucleotide (NADH) and adenosine triphosphate (ATP) content, AMO activity and the related genes abundance. Hydroquinone, detected for the first time and produced via oxidative dechlorination, as well as 4-chlorocatechol was primary transformation products of 4-CP. Nitrosomonas nitrosa AMO structural model was constructed for the first time using homology modeling. Molecular dynamics simulation suggested that the ortho-carbon in the benzene ring of 4-CP was more prone to metabolismcompared to the ipso-carbon. Density functional theory calculation revealed that 4-CP was metabolized by AMO via H-abstraction-OH-rebound reaction, with a significantly higher rebound barrier at the ipso-carbon (16.37 kcal·mol-1) as compared to the ortho-carbon (6.7 kcal·mol-1). This study fills the knowledge gap on the molecular mechanism of AMO-mediated cometabolism of organic pollutants, providing practical and theoretical foundations for improving volatile organic pollutants removal through nitrifying MABR.

Deciphering the adaptation mechanism of anammox consortia under sulfamethoxazole stress: A model coupling resistance accumulation and interspecies-cooperation

Sulfamethoxazole (SMX) is frequently detected in wastewater where anammox applications are promising. While it has been demonstrated that anammox consortia can adapt to SMX stress, the underlying community adaptation strategy has not yet been fully addressed. Therefore, in this study, we initially ascertained anammox consortia's ability to co-metabolize SMX in batch tests. Then, a 200-day domestication process of anammox consortia under SMX stress was carried out with community variations and transcriptional activities monitored by metagenomic and metatranscriptomic sequencing techniques. Despite the initial drop to 41.88 %, the nitrogen removal efficiency of the anammox consortia rebounded to 84.64 % post-domestication under 5 mg/L SMX. Meanwhile, a 4.85-fold accumulation of antibiotic resistance genes (ARGs) under SMX stress was observed as compared to the control group. Interestingly, the anammox consortia may unlock the SMX-inhibited folate synthesis pathway through a novel interspecies cooperation triangle among Nitrospira (NAA), Desulfobacillus denitrificans (DSS1), and the core anammox population Candidatus Brocadia sinica (AMX1), in which the modified dihydropteroate synthase (encoded by sul1) of NAA reconnected the symbiotic cooperation between AMX1 and DSS1. Overall, this study provides a new model for the adaptation strategies of anammox consortia to SMX stress.

Maize (Zea mays L.) Plants Alter the Fate and Accumulate Nonextractable Residues of Sulfamethoxazole in Farmland Soil

The fate of sulfonamide antibiotics in farmlands is crucial for food and ecological safety, yet it remains unclear. We used [phenyl-U-14C]-labeled sulfamethoxazole (14C-SMX) to quantitatively investigate the fate of SMX in a soil-maize system for 60 days, based on a six-pool fate model. Formation of nonextractable residues (NERs) was the predominant fate for SMX in unplanted soil, accompanied by minor mineralization. Notably, maize plants significantly increased SMX dissipation (kinetic constant kd = 0.30 day-1 vs 0.17 day-1), while substantially reducing the NER formation (92% vs 58% of initially applied SMX) and accumulating SMX (40%, mostly bound to roots). Significant NERs (maximal 29-42%) were formed via physicochemical entrapment (determined using silylation), which could partially be released and taken up by maize plants. The NERs consisted of a considerable amount of SMX formed via entrapment (1-8%) and alkali-hydrolyzable covalent bonds (2-12%, possibly amide linkage). Six and 10 transformation products were quantified in soil extracts and NERs, respectively, including products of hydroxyl substitution, deamination, and N-acylation, among which N-lactylated SMX was found for the first time. Our findings reveal the composition and instability of SMX-derived NERs in the soil-plant system and underscore the need to study the long-term impacts of reversible NERs.

Interaction patterns and keystone taxa of bacterial and eukaryotic communities during sulfamethoxazole mineralization in lake sediment

Sulfamethoxazole (SMX) is a common antibiotic pollutant in aquatic environments, which is highly persistent under various conditions and significantly contributes to the spread of antibiotic resistance. Biodegradation is the major pathway to eliminate antibiotics in the natural environment. The roles of bacteria and eukaryotes in the biodegradation of antibiotics have received considerable attention; however, their successions and co-occurrence patterns during the biodegradation of antibiotics remain unexplored. In this study, 13C-labled SMX was amended to sediment samples from Zhushan Bay (ZS), West Shore (WS), and Gonghu Bay (GH) in Taihu Lake to explore the interplay of bacterial and eukaryotic communities during a 30-day incubation period. The cumulative SMX mineralization on day 30 ranged from 5.2 % to 19.3 %, which was the highest in WS and the lowest in GH. The bacterial community showed larger within-group interactions than between-group interactions, and the positive interactions decreased during incubation. However, the eukaryotic community displayed larger between-group interactions than within-group interactions, and the positive interactions increased during incubation. The proportion of negative interactions between bacteria and eukaryotes increased during incubation. Fifty genera (including 46 bacterial and 4 eukaryotic genera) were identified as the keystone taxa due to their dominance in the co-occurrence network and tolerance to SMX. The cumulative relative abundance of these keystone taxa significantly increased during incubation and was consistent with the SMX mineralization rate. These taxa closely cooperated and played vital roles in co-occurrence networks and microbial community interactions, signifying their crucial role in SMX mineralization. These findings broadened our understanding of the complex interactions of microorganisms under SMX exposure and their potential functions during SMX mineralization, providing valuable insights for in situ bioremediation.

Cooperation among nitrifying microorganisms promotes the irreversible biotransformation of sulfamonomethoxine

Ammonia-oxidizing microorganisms, including AOA (ammonia-oxidizing archaea), AOB (ammonia-oxidizing bacteria), and Comammox (complete ammonia oxidization) Nitrospira, have been reported to possess the capability for the biotransformation of sulfonamide antibiotics. However, given that nitrifying microorganisms coexist and operate as communities in the nitrification process, it is surprising that there is a scarcity of studies investigating how their interactions would affect the biotransformation of sulfonamide antibiotics. This study aims to investigate the sulfamonomethoxine (SMM) removal efficiency and mechanisms among pure cultures of phylogenetically distinct nitrifiers and their combinations. Our findings revealed that AOA demonstrated the highest SMM removal efficiency and rate among the pure cultures, followed by Comammox Nitrospira, NOB, and AOB. However, the biotransformation of SMM by AOA N. gargensis is reversible, and the removal efficiency significantly decreased from 63.84 % at 167 h to 26.41 % at 807 h. On the contrary, the co-culture of AOA and NOB demonstrated enhanced and irreversible SMM removal efficiency compared to AOA alone. Furthermore, the presence of NOB altered the SMM biotransformation of AOA by metabolizing TP202 differently, possibly resulting from reduced nitrite accumulation. This study offers novel insights into the potential application of nitrifying communities for the removal of sulfonamide antibiotics (SAs) in engineered ecosystems.

Fate of sulfamethoxazole in wetland sediment under controlled redox conditions

Redox condition is an important controlling factor for contaminant removal in constructed wetlands; however, the redox-sensitivity of antibiotic removal in wetland sediments under controlled conditions with specific electron acceptors remains unclear. Here, using a 14C radioactive tracer, we explored fate of sulfamethoxazole (SMX) in a wetland sediment slurry under oxic, nitrate-reducing, iron-reducing, and methanogenic conditions. In the sterile treatment, unlike the comparable SMX dissipation from the water phase under four redox conditions, non-extractable residues (NERs) of SMX was highest formed in the sediment under oxic condition, mainly in sequestered and ester/amide-linked forms. Microorganisms markedly promoted SMX transformation in the slurry. The dissipation rate of SMX and its transformation products (TPs) followed the order: oxic ≈ iron-reducing > methanogenic >> nitrate-reducing conditions, being consistent with the dynamics of microbial community in the sediment, where microbial diversity was greater and networks connectivity linking dominant bacteria to SMX transformation were more complex under oxic and iron-reducing conditions. Kinetic modeling indicated that the transformation trend of SMX and its TPs into the endpoint pool NERs depended on the redox conditions. Addition of wetland plant exudates and sediment dissolved organic matter at environmental concentrations affected neither the abiotic nor the biotic transformation of SMX. Overall, the iron-reducing condition was proven the most favorable and eco-friendly for SMX transformation, as it resulted in a high rate of SMX dissipation from water without an increase in toxicity and subsequent formation of significant stable NERs in sediment. Our study comprehensively revealed the abiotic and biotic transformation processes of SMX under controlled redox conditions and demonstrated iron-reducing condition allowing optimal removal of SMX in constructed wetlands.

Favipiravir biotransformation by a side-stream partial nitritation sludge: Transformation mechanisms, pathways and toxicity evaluation

Information on biotransformation of antivirals in the side-stream partial nitritation (PN) process was limited. In this study, a side-stream PN sludge was adopted to investigate favipiravir biotransformation under controlled ammonium and pH levels. Results showed that free nitrous acid (FNA) was an important factor that inhibited ammonia oxidation and the cometabolic biodegradation of favipiravir induced by ammonia oxidizing bacteria (AOB). The removal efficiency of favipiravir reached 12.6% and 35.0% within 6 days at the average FNA concentrations of 0.07 and 0.02 mg-N L-1, respectively. AOB-induced cometabolism was the sole contributing mechanism to favipiravir removal, excluding AOB-induced metabolism and heterotrophic bacteria-induced biodegradation. The growth of Escherichia coli was inhibited by favipiravir, while the AOB-induced cometabolism facilitated the alleviation of the antimicrobial activities with the formed transformation products. The biotransformation pathways were proposed based on the roughly identified structures of transformation products, which mainly involved hydroxylation, nitration, dehydrogenation and covalent bond breaking under enzymatic conditions. The findings would provide insights on enriching AOB abundance and enhancing AOB-induced cometabolism under FNA stress when targeting higher removal of antivirals during the side-stream wastewater treatment processes.

Enzyme-induced reactive oxygen species trigger oxidative degradation of sulfamethoxazole within a methanotrophic biofilm

Although microorganisms carrying copper-containing membrane-bound monooxygenase (CuMMOs), such as particulate methane monooxygenase (pMMO) and ammonia monooxygenase (AMO), have been extensively documented for their capability to degrade organic micropollutants (OMPs), the underlying reactive mechanism remains elusive. In this study, we for the first time demonstrate biogenic reactive oxygen species (ROS) play important roles in the degradation of sulfamethoxazole (SMX), a representative OMP, within a methane-fed biofilm. Highly-efficient and consistent SMX biodegradation was achieved in a CH4-based membrane biofilm reactor (MBfR), manifesting a remarkable SMX removal rate of 1210.6 ± 39.0 μg·L-1·d-1. Enzyme inhibition and ROS clearance experiments confirmed the significant contribution of ROS, which were generated through the catalytic reaction of pMMO and AMO enzymes, in facilitating SMX degradation. Through a combination of density functional theory (DFT) calculations, electron paramagnetic resonance (EPR) analysis, and transformation product detection, we elucidated that the ROS primarily targeted the aniline group in the SMX molecule, inducing the formation of aromatic radicals and its progressive mineralization. In contrast, the isoxazole-ring was not susceptible to electrophilic ROS attacks, leading to accumulation of 3-amino-5-methylisoxazole (3A5MI). Furthermore, microbiological analysis suggested Methylosarcina (a methanotroph) and Candidatus Nitrosotenuis (an ammonia-oxidizing archaea) collaborated as the SMX degraders, who carried highly conserved and expressed CuMMOs (pMMO and AMO) for ROS generation, thereby triggering the oxidative degradation of SMX. This study deciphers SMX biodegradation through a fresh perspective of free radical chemistry, and concurrently providing a theoretical framework for the advancement of environmental biotechnologies aimed at OMP removal.

Transformation process and phytotoxicity of sulfamethoxazole and N4-acetyl-sulfamethoxazole in rice

Sulfonamide antibiotics, extensively used in human and veterinary therapy, accumulate in agroecosystem soils through livestock manure and sewage irrigation. However, the interaction between sulfonamides and rice plants remains unclear. This study investigated the transformation behavior and toxicity of sulfamethoxazole (SMX) and its main metabolite, N4-acetyl-sulfamethoxazole (NASMX) in rice. SMX and NASMX were rapidly taken up by roots and translocated acropetally. NASMX showed higher accumulating capacity, with NASMX concentrations up to 20.36 ± 1.98 μg/g (roots) and 5.62 ± 1.17 μg/g (shoots), and with SMX concentrations up to 15.97 ± 2.53 μg/g (roots) and 3.22 ± 0.789 μg/g (shoots). A total of 18 intermediate transformation products of SMX were identified by nontarget screening using Orbitrap-HRMS, revealing pathways such as deamination, hydroxylation, acetylation, formylation, and glycosylation. Notably, NASMX transformed back into SMX in rice, a novel finding. Transcriptomic analysis highlights the involvements of cytochrome P450 (CYP450), acetyltransferase (ACEs) and glycosyltransferases (GTs) in these biotransformation pathways. Moreover, exposure to SMX and NASMX disrupts TCA cycle, amino acid, linoleic acid, nucleotide metabolism, and phenylpropanoid biosynthesis pathways of rice, with NASMX exerting a stronger impact on metabolic networks. These findings elucidate the sulfonamides' metabolism, phytotoxicity mechanisms, and contribute to assessing food safety and human exposure risk amid antibiotic pollution.

Biodegradation of sulfadiazine by ryegrass (Lolium perenne L.) in a soil system: Analysis of detoxification mechanisms, transcriptome, and bacterial communities

The indiscriminate use of sulfadiazine has caused severe harm to the environment, and biodegradation is a viable method for the removal of sulfadiazine. However, there are few studies that consider sulfadiazine biodegradation mechanisms. To comprehensively investigate the process of sulfadiazine biodegradation by plants in a soil system, a potted system that included ryegrass and soil was constructed in this study. The removal of sulfadiazine from the system was found to be greater than 95% by determining the sulfadiazine residue. During the sulfadiazine removal process, a significant decrease in ryegrass growth and a significant increase in antioxidant enzyme activity were observed, which indicates the toxic response and detoxification mechanism of sulfadiazine on ryegrass. The ryegrass transcriptome and soil bacterial communities were further investigated. These results revealed that most of the differentially expressed genes (DEGs) were enriched in the CYP450 enzyme family and phenylpropanoid biosynthesis pathway after sulfadiazine exposure. The expression of these genes was significantly upregulated. Sulfadiazine significantly increased the abundance of Vicinamibacteraceae, RB41, Ramlibacter, and Microvirga in the soil. These key genes and bacteria play an important role in sulfadiazine biodegradation. Through network analysis of the relationship between the DEGs and soil bacteria, it was found that many soil bacteria promote the expression of plant metabolic genes. This mutual promotion enhanced the sulfadiazine biodegradation in the soil system. This study demonstrated that this pot system could substantially remove sulfadiazine and elucidated the biodegradation mechanism through changes in plants and soil bacteria.

Optimizing ciprofloxacin removal through regulations of trophic modes and FNA levels in a moving bed biofilm reactor performing sidestream partial nitritation

The performance of partial nitritation (PN)-moving bed biofilm reactor (MBBR) in removal of antibiotics in the sidestream wastewater has not been investigated so far. In this work, the removal of ciprofloxacin was assessed under varying free nitrous acid (FNA) levels and different trophic modes. For the first time, a positive correlation was observed between ciprofloxacin removal and FNA levels, either in the autotrophic PN-MBBR or in the mixotrophic PN-MBBR, mainly ascribed to the FNA-stimulating effect on heterotrophic bacteria (HB)-induced biodegradation. The maximum ciprofloxacin removal efficiency (∼98 %) and removal rate constant (0.021 L g-1 SS h-1) were obtained in the mixotrophic PN-MBBR at an average FNA level of 0.056 mg-N L-1, which were 5.8 and 51.2 times higher than the corresponding values in the autotrophic PN-MBBR at 0 mg FNA-N L-1. Increasing FNA from 0.006 to 0.056 mg-N L-1 would inhibit ammonia oxidizing bacteria (AOB)-induced cometabolism and metabolism from 10.2 % and 6.9 % to 6.2 % and 6.4 %, respectively, while HB-induced cometabolism and metabolism increased from 31.2 % and 22.7 % to 41.9 % and 34.5 %, respectively. HB-induced cometabolism became the predominant biodegradation pathway (75.9 %-85.8 %) in the mixotrophic mode. Less antimicrobial biotransformation products without the piperazine or fluorine were newly identified to propose potential degradation pathways, corresponding to microbial-induced metabolic types and FNA levels. This work shed light on enhancing antibiotic removal via regulating both FNA accumulation and organic carbon addition in the PN-MBBR process treating sidestream wastewater.

Effects of zero-valent iron (ZVI) on nitrogen conversion, transformation of sulfamethoxazole (SMX) and abundance of antibiotic resistance genes (ARGs) in aerobic granular sludge process

Even after pre-treatment, livestock and poultry wastewater still contain high concentrations of ammonia and residual antibiotics. These could be removed economically using the aerobic granular sludge (AGS) process with zero-valent iron (ZVI). The interaction of antibiotics and nitrogen in this process needs to be clarified and controlled, however, to achieve good removal performance. Otherwise, antibiotics might generate transformation products (TPs) with higher toxicity and lead to the emergence of antibiotic-resistant bacteria carrying antibiotic resistance genes (ARGs), which could cause persistent toxicity and the risk of disease transmission to the ecological environment. This study investigated the impact of ZVI on AGS for nitrogen and sulfamethoxazole (SMX) removal. The results show that AGS could maintain good ammonia removal performance and that the existence of SMX had a negative impact on ammonia oxidation activities. ZVI contributed to an increase in the abundance of nitrite oxidation bacteria, denitrifying bacteria and the functional genes of nitrogen removal. This led to better total nitrogen removal and a decrease in N2O emission. Accompanied by biological nitrogen transformation, SMX could be transformed into 14 TPs through five pathways. ZVI has the potential to enhance transformation pathways with TPs of lower ecotoxicity, thereby reducing the acute and chronic toxicity of the effluent. Unfortunately, ZVI might enhance the abundance of sul1, sul2, and sul3 in AGS, which increases the risk of sulfonamide antibiotic resistance. In AGS, Opitutaceae, Xanthomonas, Spartobacteria and Mesorhizobium were potential hosts for ARGs. This study provides theoretical references for the interaction of typical antibiotics and nitrogen in the biological treatment process of wastewater and bioremediation of natural water bodies.

Assessing the activity of different plant-derived molecules and potential biological nitrification inhibitors on a range of soil ammonia- and nitrite-oxidizing strains

IMPORTANCE

Synthetic nitrification inhibitors are routinely used with nitrogen fertilizers to reduce nitrogen losses from agroecosystems, despite having drawbacks like poor efficiency, cost, and entry into the food chain. Plant-derived BNIs constitute a more environmentally conducive alternative. Knowledge on the activity of BNIs to soil nitrifiers is largely based on bioassays with a single Nitrosomonas europaea strain which does not constitute a dominant member of the community of ammonia-oxidizing microorganisms (AOM) in soil. We determined the activity of several plant-derived molecules reported as having activity, including the recently discovered maize-isolated BNI, zeanone, and its natural analog, 2-methoxy-1,4-naphthoquinone, on a range of ecologically relevant AOM and one nitrite-oxidizing bacterial culture, expanding our knowledge on the intrinsic inhibition potential of BNIs toward AOM and highlighting the necessity for a deeper understanding of the effect of BNIs on the overall soil microbiome integrity before their further use in agricultural settings.

Characteristics of compounds with strong or weak nitrification inhibition in sewage

To clarify the characteristics of compounds with strong or weak nitrification inhibition in sewage, 64 organic compounds including compounds registered in Pollutant Release and Transfer Register (PRTR) were evaluated in terms of their chemical structures and molecular weights. Nineteen compounds showed strong nitrification inhibition by testing with Nitrosomonas europaea. Compounds with thioamide structures had the lowest median value of EC50 (0.017 mg/L), followed by those with alkyne structures (0.121 mg/L), chlorophenol structures (0.300 mg/L), and then azole structures (0.365 mg/L). In contrast, 33 of the 64 compounds showed weak nitrification inhibition at a concentration of 10 mg/L, 27 of which were categorized into three main groups: long-chain alcohol structures, alkyne structures with a phenyl group, and aromatic structures. Most compounds with strong nitrification inhibition had a low molecular weight (MW) from 50 to 200. Meanwhile, the proportion of compounds with weak nitrification inhibition tended to be greater with increasing MW and such compounds were predominant at higher molecular weights above 300. The correlations of results derived from tests of nitrification inhibition based on ISO 9509 and N. europaea showed that 24 out of 30 compounds provided results that were highly correlated between these tests (R = 0.85), while 4 compounds with chlorophenol structures and 2 compounds with alkyne structures showed weaker inhibition rates in the ISO 9509 test than in the N. europaea test. Our results indicate that the magnitude of nitrification inhibition depends on MW in addition to the chemical structure, which is helpful in the search for the cause of nitrification inhibition in wastewater treatment plants.

Biodegradation of trace sulfonamide antibiotics accelerated by substrates across oxic to anoxic conditions during column infiltration experiments

Frequent occurrence of trace organic contaminants in aquatic environments, such as sulfonamide antibiotics in rivers receiving reclaimed water, is concerning. Natural attenuation by soil and sediment is increasingly relied upon. In the case of riverbank filtration for water purification, the reliability of antibiotic attenuation has been called into question due to incomplete understanding of their degradation processes. This study investigated influence of substrates and redox evolution along infiltration path on biotransformation of sulfonamides. Eight sand columns (length: 28 cm) with a riverbed sediment layer at 3-8 cm were fed by groundwater-sourced tap water spiked with 1 μg/L of sulfadiazine (SDZ), sulfamethazine (SMZ), and sulfamethoxazole (SMX) each, with or without amendments of dissolved organic carbon (5 mg-C/L of 1:1 yeast and humics) or ammonium (5 mg-N/L). Two flow rates were tested over 120 days (0.5 mL/min and 0.1 mL/min). Iron-reducing conditions persisted in all columns for 27 days during the initial high flow period due to respiration of sediment organics, evolving to less reducing conditions until the subsequent low flow period to resume more reducing conditions. With surplus substrates, the spatial and temporal patterns of redox conditions differentiated among columns. The removal of SDZ and SMZ in effluents was usually low (15 ± 11%) even with carbon addition (14 ± 9%), increasing to 33 ± 23% with ammonium addition. By contrast, SMX removal was higher and more consistent among columns (46 ± 21%), with the maximum of 64 ± 9% under iron-reducing conditions. When sulfonamide removal was compared between columns for the same redox zones during infiltration, their enhancements were always associated with the availability of dissolved or particulate substrates, suggesting co-metabolism. Manipulation of the exposure time to optimal redox conditions with substrate amendments, rather than to simply prolong the overall residence time, is recommended for nature-based solutions to tackle target antibiotics.

Effects of successional sulfadiazine exposure on biofilm in moving bed biofilm reactor: Secretion of extracellular polymeric substances, community activity and functional gene expression

The effects of sulfadiazine (SDZ) on responses of biofilm in a moving bed biofilm reactor were explored with emphasis on the changes in extracellular polymeric substances (EPS) and functional genes. It was found that 3 to 10 mg/L SDZ reduced the protein (PN) and polysaccharide (PS) contents of EPS by 28.7%-55.1% and 33.3%-61.4%, respectively. The EPS maintained high ratio of PN to PS (10.3-15.1), and the major functional groups within EPS remained unaffected to SDZ. Bioinformatics analysis showed that SDZ significantly altered the community activity such as increased expression of s_Alcaligenes faecali. Totally, the biofilm held high SDZ removal rates, which were ascribed to the self-protection by secreted EPS, and genes levels upregulation of antibiotic resistance and transporter protein. Collectively, this study provides more details on the biofilm community exposure to an antibiotic and highlights the role of EPS and functional genes in antibiotic removal.

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.

Revealing specific transformation pattern of sulfonamides during wastewater biological treatment processes by molecular networking nontarget screening

Biotransformation of emerging contaminants (ECs) is of importance in various natural and engineered systems to eliminate the adverse effects of ECs toward organisms. In wastewater, structurally similar ECs may transform through similar reactions triggered by common enzymes. However, the transformation pattern for them was scarcely studied. To fill the research gaps, five sulfonamides were chosen as the targeted ECs with similar structure to explore the transformation pattern in wastewater biological treatment experiments at lab scale. Through molecular networking based nontarget screening, 45 transformation products (TPs) of sulfonamides were identified and 14 of them were newly found. On the basis, five specific transformation patterns were summarized for sulfonamides by transformation pathways comparing, reaction frequency analyzing and dominant TPs comparing. Results suggested that pterin-chelation and formylation (dominant transformation pathway) and acetylation, methylation and deamination reactions were commonly occurred for sulfonamides in wastewater. Among them, the role of formylation as the dominant transformation pathway for sulfonamides transformed in wastewater was firstly reported in present study. Subsequent frontier molecular orbital calculation suggested the active site of amino (N₁H₂-) may contribute the specific transformation pattern of sulfonamides. Present study reveals the specific transformation pattern of sulfonamides from the aspect of TPs and transformation pathways. In the future, knowledge on the specific transformation pattern can be used to regulate and enhance the removal of a class of ECs with similar structure rather than just one of ECs.

Methane-Oxidizing Activity Enhances Sulfamethoxazole Biotransformation in a Benthic Constructed Wetland Biomat

Ammonia monooxygenase and analogous oxygenase enzymes contribute to pharmaceutical biotransformation in activated sludge. In this study, we hypothesized that methane monooxygenase can enhance pharmaceutical biotransformation within the benthic, diffuse periphytic sediments (i.e., "biomat") of a shallow, open-water constructed wetland. To test this hypothesis, we combined field-scale metatranscriptomics, porewater geochemistry, and methane gas fluxes to inform microcosms targeting methane monooxygenase activity and its potential role in pharmaceutical biotransformation. In the field, sulfamethoxazole concentrations decreased within surficial biomat layers where genes encoding for the particulate methane monooxygenase (pMMO) were transcribed by a novel methanotroph classified as Methylotetracoccus. Inhibition microcosms provided independent confirmation that methane oxidation was mediated by the pMMO. In these same incubations, sulfamethoxazole biotransformation was stimulated proportional to aerobic methane-oxidizing activity and exhibited negligible removal in the absence of methane, in the presence of methane and pMMO inhibitors, and under anoxia. Nitrate reduction was similarly enhanced under aerobic methane-oxidizing conditions with rates several times faster than for canonical denitrification. Collectively, our results provide convergent in situ and laboratory evidence that methane-oxidizing activity can enhance sulfamethoxazole biotransformation, with possible implications for the combined removal of nitrogen and trace organic contaminants in wetland sediments.

Effect of antibiotic cocktail exposure on functional disturbance of nitrifying microbiome

The present study quantitatively determined the degree and type of functional disturbance in the nitrifying microbiome caused by exposure to a single oxytetracycline (OTC) and a two-antibiotic mixture containing OTC and sulfamethoxazole (SMX). While the single antibiotic had a pulsed disturbance on nitritation that was recoverable within three weeks, the antibiotic mixture caused a more significant pulsed disturbance on nitritation and a potential press disturbance on nitratation that was not recoverable for over five months. Bioinformatic analysis revealed significant perturbations for both canonical nitrite-oxidizing (Nitrospira defluvii) and potential complete ammonium-oxidizing (Ca. Nitrospira nitrificans) populations that were strongly associated with the press perturbation on nitratation. In addition to this functional disturbance, the antibiotic mixture reduced the biosorption of OTC and altered its biotransformation pathways, resulting in different transformation products compared with those produced when OTC was treated as a single antibiotic. Collectively, this work elucidated how the antibiotic mixture can affect the degree, type, and duration of the functional disturbance on nitrifying microbiome and offer new insights into the environmental consequences of antibiotic residues (e.g., their fate, transformation, and ecotoxicity) when present as an antibiotic mixture rather than single antibiotics.

Impact of antibiotics on microbial community in aquatic environment and biodegradation mechanism: a review and bibliometric analysis

Antibiotic residues in aquatic environments pose a potential hazard, and microbes, which play important roles in aquatic ecosystems, are vulnerable to the impacts of antibiotics. This study aimed to analyze the research progress, trends, and hot topics of the impact of antibiotics on microbial community and biodegradation mechanism using bibliometric analysis. An in-depth analysis of the publication characteristics of 6143 articles published between 1990 and 2021 revealed that the number of articles published increased exponentially. The research sites have been mainly concentrated in the Yamuna River, Pearl River, Lake Taihu, Lake Michigan, Danjiangkou Reservoir, etc., illustrating that research around the world is not even. Antibiotics could change the diversity, structure, and ecological functions of bacterial communities, stimulate a widespread abundance of antibiotic-resistant bacteria and antibiotic-resistant genes, and increase the diversity of eukaryotes, thus triggering the shift of food web structure to predatory and pathogenic. Latent Dirichlet allocation theme model analysis showed three clusters, and the research hotspots mainly included the effect of antibiotics on the denitrification process, microplastics combined with antibiotics, and methods for removing antibiotics. Furthermore, the mechanisms of microbe-mediated antibiotic degradation were unraveled, and importantly, we provided bottlenecks and future research perspectives on antibiotics and microbial diversity research.

Responses of biofilm communities in a hybrid moving bed biofilm reactor-membrane bioreactor system to sulfadiazine antibiotic exposure

Antibiotics in wastewater can affect the structures and functions of bacterial communities, subsequently influencing how well a biological process performs. Therefore, the characteristics of bacterial community were investigated in a hybrid moving bed biofilm reactor-membrane bioreactor system when treating domestic wastewater containing sulfadiazine (SDZ). Results indicated total nitrogen removal reduced by 10.2%, 9.1%, 2.7% and 2.9%, respectively, with increasing carbon to nitrogen (C/N) ratios (2.5, 4, 6 and 9) when SDZ was present (0.5 mg/L). The microbial communities' analysis revealed that the abundance of nitrogen removal-related bacteria increased with C/N. Specifically, the abundance of ammonia-oxidizing bacteria (0.46%-0.90%) was low, and the nitrite-oxidizing bacteria (2.16%-7.13%) and denitrifying bacteria showed a significant increase (Hyphomicrobium: 0.57%-3.54%) when C/N ratio increased. The abundance of denitrifying bacterial declined by 4.82-8.56% at different C/N ratios, while nitrifying bacterial rose by 0.70-5.67%. Interestingly, the denitrifying bacteria Enterobacter, Sphingomonas and Gemmatimonas acted as mutualistic bacteria that stabilized denitrification.

Benzimidazole fungicide biotransformation by comammox Nitrospira bacteria: Transformation pathways and associated proteomic responses

Benzimidazole fungicides are frequently detected in aquatic environments and pose a serious health risk. Here, we investigated the metabolic capacity of the recently discovered complete ammonia-oxidizing (comammox) Nitrospira inopinata and kreftii to transform a representative set of benzimidazole fungicides (i.e., benzimidazole, albendazole, carbendazim, fuberidazole, and thiabendazole). Ammonia-oxidizing bacteria and archaea, as well as the canonical nitrite-oxidizing Nitrospira exhibited no or minor biotransformation activity towards all the five benzimidazole fungicides. In contrast, the investigated comammox bacteria actively transformed all the five benzimidazole fungicides, except for thiabendazole. The identified transformation products indicated hydroxylation, S-oxidation, and glycosylation as the major biotransformation pathways of benzimidazole fungicides. We speculated that these reactions were catalyzed by comammox-specific ammonia monooxygenase, cytochrome P450 monooxygenases, and glycosylases, respectively. Interestingly, the exposure to albendazole enhanced the expression of the antibiotic resistance gene acrB of Nitrospira inopinata, suggesting that some benzimidazole fungicides could act as environmental stressors that trigger cellular defense mechanisms. Altogether, this study demonstrated the distinct substrate specificity of comammox bacteria towards benzimidazole fungicides and implies their significant roles in the biotransformation of these fungicides in nitrifying environments.

Abiotic transformations of sulfamethoxazole by hydroxylamine, nitrite and nitric oxide during wastewater treatment: Kinetics, mechanisms and pH effects

Hydroxylamine (NH₂OH), nitrite (NO₂^-) and nitric oxide (NO), intermediates enzymatically formed during biological nitrogen removal processes, can engage in chemical (abiotic) transformations of antibiotics. This study determined the kinetics, mechanisms and pathways of abiotic transformations of the antibiotic sulfamethoxazole (SMX) by NH₂OH, NO₂^- and NO in a series of batch tests under different pH and oxygen conditions. While NH₂OH was not able to directly transform SMX, NO₂^- (with HNO₂ as the actual reactant) and NO can chemically transform SMX primarily through hydroxylation, nitration, deamination, nitrosation, cleavage of S-N, N-C and C-S bonds, and coupling reactions. There were substantial overlaps in transformation product formations during abiotic transformations by HNO₂^- and NO. The second order rate constants of SMX with NO₂^- and NO were determined in the range of 1.5 × 10^-1 - 4.8 × 10³ M^-1 s^-1 and 1.0 × 10² - 3.1 × 10⁴ M^-1 s^-1, respectively, under varying pH (4 - 9) and anoxic or oxic conditions. Acidic pH significantly enhanced abiotic transformation kinetics, and facilitated nitration, nitrosation, and cleavage of S-N and N-C bonds. The findings advance our understanding of the fate of antibiotics during biological nitrogen removal, and highlight the role of enzymatically formed reactive nitrogen species in the antibiotic degradation.

Biotransformation of sulfamonomethoxine in a granular sludge system: Pathways and mechanisms

The biotransformation of sulfamonomethoxine (SMM) was studied in an aerobic granular sludge (AGS) system to understand the role of sorption by microbial cells and extracellular polymeric substances (EPS) and the role of functional microbe/enzyme biodegradation. Biodegradation played a more important role than adsorption, while microbial cells covered with tightly bound EPS (TB-EPS) showed higher adsorption capacity than microbial cells themselves or microbial cells covered with both loosely bound EPS (LB-EPS) and TB-EPS. The binding tests between EPS and SMM and the spectroscopic analyses (3D-EEM, UV-Vis, and FTIR) were performed to obtain more information about the adsorption process. The data showed that SMM could interact with EPS by combining with aromatic protein compounds, fulvic acid-like substances, protein amide II, and nucleic acids. Batch tests with various substances showed that SMM removal rates were in an order of NH₂OH (60.43 ± 2.21 μg/g SS) > NH₄Cl (52.96 ± 0.30 μg/g SS) > NaNO₃ (31.88 ± 1.20 μg/g SS) > NaNO₂ (21.80 ± 0.42 μg/g SS). Hydroxylamine and hydroxylamine oxidoreductase (HAO) favored SMM biotransformation and the hydroxylamine-mediated biotransformation of SMM was more effective than others. In addition, both ammonia monooxygenase (AMO) and CYP450 were able to co-metabolize SMM. Analysis of UPLC-QTOF-MS indicated the biotransformation mechanisms, revealing that acetylation of arylamine, glucuronidation of sulfonamide, deamination, SO₂ extrusion, and δ cleavage were the five major transformation pathways. The detection of TP202 in the hydroxylamine-fed Group C indicated a new biotransformation pathway through HAO. This study contributes to a better understanding of the biotransformation of SMM.

Removal performance, biotransformation pathways and products of sulfamethoxazole in vertical subsurface flow constructed wetlands with different substrates

For decades, sulfamethoxazole (SMX) has been frequently detected in the aquatic environments due to its high usage and refractory to degradation. Constructed wetland (CW) is regarded as an efficient advanced wastewater technology to eliminate organic pollutants including SMX. In CW system, substrate adsorption and further biodegradation are extremely important in SMX removal; however, the removal performance of SMX by CWs with different substrates varies greatly, and the biotransformation pathways, products, and mechanisms of SMX remain unclear. To address this, we constructed a CW with conventional substrate (CS, gravel) as control (C-CW) and three CWs with emerging substrates (ES, biochar, zeolite and pyrite for B-CW, Z-CW and P-CW, respectively), and explored the performance and mechanisms of SMX removal in CWs. Results illustrated that the removal performance of SMX in CWs with ES reached 94.89-99.35%, and significantly higher than that with CS of 89.50% (p < 0.05). Biodegradation contributed >90% SMX removal in all CWs. The microbial compositions and functions differed among CWs at the middle layer (mixed layer), which shaped diverse resistance pattern and metabolism pathways of microbiomes under SMX stress: P-CW and B-CW cope with SMX stress by enhancing material and energy metabolism, whereas Z-CW does that by enhancing metabolism and exocytosis of xenobiotics. Additionally, nine transformation pathways with 15 transformation products were detected in this study. A reversible process of desamino-SMX being reconverted to SMX might exist in P-CW, which caused a lower SMX removal efficiency in P-CW. This study provided a comprehensive insight into the processes and mechanisms of SMX removal in CWs with different substrates, which would be a useful guidance for substrate selection in CWs in terms of enhanced micropollutants removal.

Microbial communities and processes in biofilters for post-treatment of ozonated wastewater treatment plant effluent

Ozonation is an established solution for organic micropollutant (OMP) abatement in tertiary wastewater treatment. Biofiltration is the most common process for the biological post-treatment step, which is generally required to remove undesired oxidation products from the reaction of ozone with water matrix compounds. This study comparatively investigates the effect of filter media on the removal of organic contaminants and on biofilm properties for biologically activated carbon (BAC) and anthracite biofilters. Biofilms were analysed in two pilot-scale filters that have been operated for >50,000 bed volumes as post-treatment for ozonated wastewater treatment plant effluent. In parallel, the removal performance of bulk organics and OMP, including differentiation of adsorption and biotransformation through sodium azide inhibition, were carried out in bench-scale filter columns filled with material from the pilot filters. The use of BAC instead of anthracite resulted in an improved removal of organic bulk parameters, dissolved oxygen, and OMP. The OMP removal observed in the BAC filter but not in the anthracite filter was based on adsorption for most of the investigated compounds. For valsartan, however, biotransformation was found to be the dominant pathway, indicating that conditions for biotransformation of certain OMP are better on BAC than on anthracite. Adenosine triphosphate analyses in the media-attached biofilms of the pilot filters showed that biomass concentrations in the BAC filter were significantly higher than in the anthracite filter. The microbial communities (16S rRNA gene sequencing) appeared to be similar with respect to the types of organisms occurring on both filter materials. Alpha diversity also exhibited little variation between filter media. Beta diversity analysis, however, revealed that filter media and bed depth substantially influenced the biofilm composition. In practice, the impact of filter media on biofilm properties and biotransformation processes should be considered for the design of biofilters.

The synergistic mechanism of β-lactam antibiotic removal between ammonia-oxidizing microorganisms and heterotrophs

Nitrifying system is an effective strategy to remove numerous antibiotics, however, the contribution of ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA) and heterotrophs for antibiotic removal are still unclear. In this study, the mechanism of β-lactam antibiotic (cefalexin, CFX) removal was studied in a nitrifying sludge system. Results showed that CFX was synergistically removed by AOB (Nitrosomonas, played a major role) and AOA (Candidatus_Nitrososphaera) through ammonia monooxygenase-mediated co-metabolism, and by heterotrophs (Pseudofulvimonas, Hydrogenophaga, RB41, Thauera, UTCFX1, Plasticicumulans, Phaeodactylibacter) through antibiotic resistance genes (ARGs)-encoded β-lactamases-mediated hydrolysis. Regardless of increased archaeal and heterotrophic CFX removal with the upregulation of amoA in AOA and ARGs, the system exhibited poorer CFX removal performance at 10 mg/L, mainly due to the inhibition of AOB. This study provides new reference for the important roles of heterotrophs and ARGs, opening the possibilities for the application of ARGs in antibiotic biodegradation.

Role of ammonia-oxidizing microorganisms in the removal of organic micropollutants during simulated riverbank filtration

Biodegradation plays an important role in the removal of organic micropollutants (OMPs) during riverbank filtration (RBF) for drinking water production. The ability of ammonia-oxidizing microorganisms (AOM) to remove OMPs has attracted increasing attention. However, the distribution of AOM in RBF and its role in the degradation of OMPs remains unknown. In this study, the behavior of 128 selected OMPs and the distribution of AOM and their roles in the degradation of OMPs in RBF were explored by column and batch experiments simulating the first meter of the riverbank. The results showed that the selected OMPs were effectively removed (82/128 OMPs, >70% removal) primarily by biodegradation and partly by adsorption. Inefficiently removed OMPs tended to have low molecular weights, low log P, and contain secondary amides, secondary sulfonamides, secondary ketimines, and benzyls. In terms of the microbial communities, the relative abundance of AOM increased from 0.1%-0.2% (inlet_-sand) to 5.3%-5.9% (outlet_-sand), which was dominated by ammonia-oxidizing archaea whose relative abundance increased from 23%-72% (inlet_-sand) to 97% (outlet_-sand). Comammox accounted for 23%-64% in the inlet_-sand and 1% in the outlet_-sand. The abundances of AOM amoA genes kept stable in the inlet_-sand of control columns, while decreased by 78% in the treatment columns, suggesting the inhibition effect of allylthiourea (ATU) on AOM. It is observed that AOM played an important role in the degradation of OMPs, where its inhibition led to the corresponding inhibition of 32 OMPs (5/32 were completely suppressed). In particular, OMPs with low molecular weights and containing primary amides, secondary amides, benzyls, and secondary sulfonamides were more likely to be removed by AOM. This study reveals the vital role of AOM in the removal of OMPs, deepens our understanding of the degradation of OMPs in RBF, and offers valuable insights into the physiochemical properties of OMPs and their AOM co-metabolic potential.

Comammox biogeography subject to anthropogenic interferences along a high-altitude river

The recent discovery of comammox Nitrospira performing complete ammonia oxidation to nitrate has overturned the long-held dogma of two-step nitrification on Earth, yet little is known about the effect of urbanization interference on their distribution. Using gene-centric metagenomics, we provided the first blueprints about comammox community, biogeography, and environmental drivers along a high-elevation (> 2000 m) river flowing through the largest city on the vulnerable Qinghai-Tibetan Plateau. Our study confirmed a wide presence and diversity of yet-uncultured comammox clade B across wet and dry seasons, with average 3.0 and 2.0 times as abundant as clade-A amoA genes in water and sediments, respectively. Species identified from freshwater and drinking water treatment plants dominated the comammox guilds (58∼100%), suggesting this plateau river shared a similar comammox assemblage with the above habitat types. Compared with the urban area harboring more abundant canonical Nitrospira identified in wastewater (average 24%), the upstream suburban reach had a smaller human population but larger proportions of comammox in ammonia-oxidizing prokaryotes (24∼72% of abundances) and Nitrospira sublineages I/II. Higher contents of nitrate and nitrite in water, and antibiotics in water and sediments, may restrain comammox niches in nitrifiers over the urban area. Further random forest analysis revealed that lincosamides and quinolones were the most important antibiotic predictors for the niche differentiations between comammox and canonical nitrifiers in water, while macrolides for those in sediments. Finally, by incubation experiments, we demonstrated higher activity contributions of benthic comammox in the suburban area (36.2∼92.8% of potential ammonia-oxidation rates) than in the urban reach, and that the contribution variation had significant negative relations with macrolides and their major components. Overall, this study highlighted that anthropogenic activities hampered the advantage of riverine complete nitrifiers over the canonical two-step ones.

Pharmaceutical Biotransformation is Influenced by Photosynthesis and Microbial Nitrogen Cycling in a Benthic Wetland Biomat

In shallow, open-water engineered wetlands, design parameters select for a photosynthetic microbial biomat capable of robust pharmaceutical biotransformation, yet the contributions of specific microbial processes remain unclear. Here, we combined genome-resolved metatranscriptomics and oxygen profiling of a field-scale biomat to inform laboratory inhibition microcosms amended with a suite of pharmaceuticals. Our analyses revealed a dynamic surficial layer harboring oxic-anoxic cycling and simultaneous photosynthetic, nitrifying, and denitrifying microbial transcription spanning nine bacterial phyla, with unbinned eukaryotic scaffolds suggesting a dominance of diatoms. In the laboratory, photosynthesis, nitrification, and denitrification were broadly decoupled by incubating oxic and anoxic microcosms in the presence and absence of light and nitrogen cycling enzyme inhibitors. Through combining microcosm inhibition data with field-scale metagenomics, we inferred microbial clades responsible for biotransformation associated with membrane-bound nitrate reductase activity (emtricitabine, trimethoprim, and atenolol), nitrous oxide reduction (trimethoprim), ammonium oxidation (trimethoprim and emtricitabine), and photosynthesis (metoprolol). Monitoring of transformation products of atenolol and emtricitabine confirmed that inhibition was specific to biotransformation and highlighted the value of oscillating redox environments for the further transformation of atenolol acid. Our findings shed light on microbial processes contributing to pharmaceutical biotransformation in open-water wetlands with implications for similar nature-based treatment systems.

Sulfamethoxazole Enhances Specific Enzymatic Activities under Aerobic Heterotrophic Conditions: A Metaproteomic Approach

The growing concern about antibiotic-resistant microorganisms has focused on the sludge from wastewater treatment plants (WWTPs) as a potential hotspot for their development and spread. To this end, it seems relevant to analyze the changes on the microbiota as a consequence of the antibiotics that wastewater may contain. This study aims at determining whether the presence of sulfamethoxazole (SMX), even in relatively low concentrations, modifies the microbial activities and the enzymatic expression of an activated sludge under aerobic heterotrophic conditions. For that purpose, we applied a metaproteomic approach in combination with genomic and transformation product analyses. SMX was biotransformed, and the metabolite 2,4(1H,3H)-pteridinedione-SMX (PtO-SMX) from the pterin-conjugation pathway was detected at all concentrations tested. Metaproteomics showed that SMX at 50-2000 μg/L slightly affected the microbial community structure, which was confirmed by DNA metabarcoding. Interestingly, an enhanced activity of the genus Corynebacterium and specifically of five enzymes involved in its central carbon metabolism was found at increased SMX concentrations. Our results suggest a role of Corynebacterium genus on SMX risks mitigation in our bioreactors.

A review on antibiotics removal: Leveraging the combination of grey and green techniques

Antibiotics are currently a major source of concern around the world due to the serious risks posed to human health and the environment. The performance of the secondary wastewater treatment processes/technologies (representing grey process) and constructed wetlands (CWs) (typical green process) in removing antibiotics and antibiotic resistance genes (ARG) was reviewed. The result showed that the grey process mainly removes antibiotics, but does not significantly remove ARG, and some processes may even cause ARG enrichment. The overall treatment in CWs is better than WWTPs, especially for ARG. Vertical subsurface flow CWs (VFCWs) are more conductive to antibiotics removal, while horizontal subsurface flow CWs (HFCWs) have a better ARG removal. More importantly, this review admits and suggests that the combination of grey process with green process is an effective strategy to remove antibiotics and ARG. The most advantage of the combination lies in realizing complementary advantages, i.e. the grey process as the primary treatment while CWs as the polishing stage. The efficiency of such the hybrid system is much higher than either single treatment process.

Free Nitrous Acid Inhibits Atenolol Removal during the Sidestream Partial Nitritation Process through Regulating Microbial-Induced Metabolic Types

Limited studies have attempted to evaluate pharmaceutical removal during the sidestream partial nitritation (PN) process. In this work, atenolol biodegradation by PN cultures was investigated by maintaining ammonium and pH at different levels. For the first time, free nitrous acid (FNA), other than ammonium, pH, and free ammonia, was demonstrated to inhibit atenolol removal, with biodegradation efficiencies of ∼98, ∼67, and ∼28% within 6 days at average FNA levels of 0, 0.03, and 0.19 mg-N L^-1, respectively. Ammonia-oxidizing bacteria (AOB)-induced metabolism was predominant despite varying FNA concentrations. In the absence of ammonium/FNA, atenolol was mostly biodegraded via AOB-induced metabolism (65%) and heterotroph-induced metabolism (33%). AOB-induced metabolism was largely inhibited (down to 29%) at 0.03 mg-N L^-1 FNA, while ∼27 and ∼11% were degraded via heterotroph-induced metabolism and AOB-induced cometabolism, respectively. Higher FNA (0.19 mg-N L^-1) substantially reduced atenolol biodegradation via heterotroph-induced metabolism (4%), AOB-induced metabolism (16%), and AOB-induced cometabolism (8%). Newly identified products and pathways were related to metabolic types and FNA levels: (i) deamination and decarbonylation (AOB-induced cometabolism, 0.03 mg-N L^-1 FNA); (ii) deamination from atenolol acid (heterotrophic biodegradation); and (iii) nitro-substitution (reaction with nitrite). This suggests limiting FNA to realize simultaneous nitrogen and pharmaceutical removal during the sidestream process.

Comammox bacteria predominate among ammonia-oxidizing microorganisms in municipal but not in refinery wastewater treatment plants

Comammox bacteria have proved to be one dominant and significant ammonia-oxidizing microorganisms (AOMs) in municipal wastewater treatment plants (WWTPs), however, it still remains unknown about their abundance and diversity in industrial WWTPs. In this study, activated sludge samples from 8 municipal WWTPs and 6 industrial WWTPs treating refinery wastewater were taken and analyzed using qPCR and amoA gene sequencing. Intriguingly, quantitative real-time PCR (qPCR) results suggested that comammox bacteria had a higher numerical abundance compared with ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) in municipal WWTPs but did not in refinery WWTPs. Moreover, comammox amoA sequences obtained from high-throughput sequencing were retrieved from all the 8 municipal samples but only 1 industrial sample. Further phylogenetic analysis revealed that N. nitrosa cluster accounted for as high as 79.56% of the total comammox affiliated sequences, which was the most numerically abundant comammox species in municipal WWTPs. This study provided new insights into the abundance and diversity of comammox bacteria in the biological nitrification process in municipal and refinery wastewater treatment systems.

A review of ammonia removal using a biofilm-based reactor and its challenges

Extensive growth of industries leads to uncontrolled ammonia releases to environment. This can result in significant degradation of the aquatic ecology as well as significant health concerns for humans. Knowing the mechanism of ammonia elimination is the simplest approach to comprehending it. Ammonia has been commonly converted to less hazardous substances either in the form of nitrate or nitrogen gas. Ammonia has been converted into nitrite by ammonia-oxidizing bacteria and further reduced to nitrate by nitrite-oxidizing bacteria in aerobic conditions. Denitrification takes place in an anoxic phase and nitrate is converted into nitrogen gas. It is challenging to remove ammonia by employing technologies that do not incur particularly high costs. Thus, this review paper is focused on biofilm reactors that utilize the nitrification process. Many research publications and patents on biofilm wastewater treatment have been published. However, only a tiny percentage of these projects are for full-scale applications, and the majority of the work was completed within the last few decades. The physicochemical approaches such as ammonia adsorption, coagulation-flocculation, and membrane separation, as well as conventional biological treatments including activated sludge, microalgae, and bacteria biofilm, are briefly addressed in this review paper. The effectiveness of biofilm reactors in removing ammonia was compared, and the microbes that effectively remove ammonia were thoroughly discussed. Overall, biofilm reactors can remove up to 99.7% ammonia from streams with a concentration in range of 16-900 mg/L. As many challenges were identified for ammonia removal using biofilm at a commercial scale, this study offers future perspectives on how to address the most pressing biofilm issues. This review may also improve our understanding of biofilm technologies for the removal of ammonia as well as polishing unit in wastewater treatment plants for the water reuse and recycling, supporting the circular economy concept.

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.

Light-dependent enhancement of sulfadiazine detoxification and mineralization by non-photosynthetic methanotrophs

Co-metabolism and photodegradation are two approaches for remediating trace organic compounds (TOrCs), however, interactions between the two with regards to TOrCs degradation have not been elucidated. In this study, sulfadiazine (SDZ) was chosen as a representative TOrC and Methylocystis bryophila as a typical strain. Under light conditions, about 80.6% of SDZ was removed by M. bryophila, but only 7.6% or 28.9% of SDZ was eliminated by either individual photodegradation or by co-metabolism. The SDZ stimulated more extracellular organic matter (EOM) production by M. bryophila. The enhanced SDZ degradation was attributed to indirect photolysis caused by the excited triplet state of EOM (³EOM*) and co-metabolism. The UPLC-QTOF-MS analysis showed that due to co-metabolism, the pyrimidine ring was broken and could further be oxidized into smaller molecules under light conditions, such as formic and acetic acids. The SDZ mineralization ratio increased from 9.9% under the co-metabolic condition alone to 36.5% under co-metabolism coupled with photodegradation. The Ames tests confirmed that the SDZ degradation products by co-metabolism were mutagenic, however, their toxicity was ameliorated by light during co-metabolism. In conclusion, light plays a crucial role in co-metabolic processes of TOrCs.

Sulfamethoxazole degradation by Pseudomonas silesiensis F6a isolated from bioelectrochemical technology-integrated constructed wetlands

The antibiotic-degrading ability and mechanism of the bacteria in the novel and ecological bioelectrochemical technology-integrated constructed wetlands (BICW) remain unknown. In this study, the sulfamethoxazole (SMX) degrading strain Pseudomonas silesiensis F6a (F6a), which had high degradation efficiency, was firstly isolated from a substrate sample in BICW. The SMX degradation process of F6a follows pseudo first order kinetics. Four metabolic pathways and twelve degradation products were identified. Based on genomics and proteomics analysis, six key SMX-degrading genes, Gene4641 deoC, Gene0552 narI, Gene0546 luxS, Gene1753 nuoH, Gene0655 and Gene4650, were identified, which were mainly participated in C-S cleavage, S-N hydrolysis and isoxazole ring cleavage. Interestingly, we found the corresponding sulfonamides resistance genes were not detected in F6a, which may provide an evidence for low abundance of the sulfonamides resistance genes in BICW system. These findings would contribute to a better understanding of biotransformation of antibiotic in the BICW.

Towards a more labor-saving way in microbial ammonium oxidation: A review on complete ammonia oxidization (comammox)

In the Anthropocene, nitrogen pollution is becoming an increasing challenge for both mankind and the Earth system. Microbial nitrogen cycling begins with aerobic nitrification, which is also the key rate-limiting step. For over a century, it has been accepted that nitrification occurs sequentially involving ammonia oxidation, which produces nitrite followed by nitrite oxidation, generating nitrate. This perception was changed by the discovery of comammox Nitrospira bacteria and their metabolic pathway. In addition, this also provided us with new knowledge concerning the complex nitrogen cycle network. In the comammox process, ammonia can be completely oxidized to nitrate in one cell via the subsequent activity of the enzyme complexes, ammonia monooxygenase, hydroxylamine dehydrogenase, and nitrite oxidodreductase. Over the past five years, research on comammox made great progress. However, there still exist a lot of questions, including how much does comammox contribute to nitrification? How large is the diversity and are there new strains to be discovered? Do comammox bacteria produce the greenhouse gas N₂O, and how or to which extent may they contribute to global climate change? The above four aspects are of great significance on the farmland nitrogen management, aquatic environment restoration, and mitigation of global climate change. As large number of comammox bacteria and pathways have been detected in various terrestrial and aquatic ecosystems, indicating that the comammox process may exert an important role in the global nitrogen cycle.

Environmental impacts of antibiotics addition to algal-bacterial-based aquaponic system

Antibiotics usage is a double-edged sword among the production promotion and environmental aggravation of aquaculture system. In this study, the effects of sulfadiazine addition on algal-bacterial-based aquaponic (AA) system were thoroughly investigated. Results showed that sulfadiazine addition increased the nitrogen (N) and carbon (C) recovery of AA system by 1.3 times and 2.9 times, respectively. Meanwhile, the global warming potential was increased by 63% due to aggravated nitrous oxide (N₂O) emission. This was mainly because sulfadiazine increased the abundance of nirS genes and decreased the abundance of nosZ genes, which subsequently led to higher N₂O accumulation. Furthermore, resistance gene (sul-1, sul-2, and intI-1) abundance in the treatment group was an order higher than that of the control group, which would give rise to the environmental risk for agroecological system. KEY POINTS: • Sulfadiazine addition increased NUE at expense of aggravated GHG emissions. • Sulfadiazine disrupted the balance between the abundance of nirS and nosZ genes. • Sulfadiazine addition increased the resistance gene abundance of AA system.

Insight into integration of photocatalytic and microbial wastewater treatment technologies for recalcitrant organic pollutants: From sequential to simultaneous reactions

The more and more stringent environmental standards for recalcitrant organic pollutants pushed forward the development of integration of photocatalytic and microbial wastewater treatment technologies. The past studies proposed mainly two typical integration ways: a) Independent sequence of photocatalysis and biodegradation (ISPB) conducting the sequential reactions; b) Intimate coupling of photocatalysis and biodegradation (ICPB) conducting the simultaneous reactions. Although ICPB has received more attraction recently due to its novelty, ISPB gives an edge in certain cases. The article reviews the state-of-the-art ISPB and ICPB studies to comprehensively compare the two systems. The strengths and weaknesses of ISPB and ICPB regarding the treatment efficiency, cost, toxicity endurance and flexibility are contradistinguished. The reactor set-ups, photocatalysts, microbial characteristics of ISPB and ICPB are summarized. The applications for different kinds of recalcitrant compounds are elaborated to give a holistic view of the removal efficiencies and transformation pathways by the two technologies. Currently, in-depth understandings about the interference among mixed pollutants, co-existing components and key parameters in realistic wastewater are urgently needed. The long-term and large-scale application cases of the integration technologies are still rare. Overall, we conclude that both ISPB and ICPB technologies are reaching maturity while challenges still exist for two systems especially regarding the reliability, economy and generalization for realistic wastewater treatment plants. Future research should not only manage to reduce the cost and energy consumption by upgrading reactors and developing novel catalysts, but also attach importance to the cocktail effects of wastewater during the sequential or simultaneous photocatalysis and biodegradation.

Determination of the lower limits of antibiotic biodegradation and the fate of antibiotic resistant genes in activated sludge: Both nitrifying bacteria and heterotrophic bacteria matter

Antibiotics can be biodegraded in activated sludge via co-metabolism and metabolism. In this study, we investigated the biodegradation pathways of sulfamethoxazole (SMX) and antibiotic resistant genes' (ARGs) fate in different autotrophic and heterotrophic microorganisms, by employing aerobic sludge, mixed sludge, and nitrifying sludge. A threshold concentration of SMX activating the degradation pathways in the initial stage of antibiotics degradation was found and proved in different activated sludge systems. Heterotrophic bacteria played an important role in SMX biodegradation. However, ammonia-oxidizing bacteria (AOB) had a faster metabolic rate, which was about 15 times higher than heterotrophic bacteria, contributing much to SMX removal via co-metabolism. As SMX concentration increases, the amoA gene and AOB relative abundance decreased in aerobic sludge due to the enrichment of functional heterotrophic bacteria, while it increased in nitrifying sludge. Microbial community analysis showed that functional bacteria which possess the capacity of SMX removal and antibiotic resistance were selected by SMX pressure. Potential ARGs hosts could increase their resistance to the biotoxicity of SMX and maintain system performance. These findings are of practical significance to guide antibiotic biodegradation and ARGs control in wastewater treatment plants.

Cometabolic biodegradation of antibiotics by ammonia oxidizing microorganisms during wastewater treatment processes

Studies on antibiotic removal during wastewater treatment processes are crucial since their release into the environment could bring potential threats to human health and ecosystem. Cometabolic biodegradation of antibiotics by ammonia oxidizing microorganisms (AOMs) has received special attentions due to the enhanced removal of antibiotics during nitrification processes. However, the interactions between antibiotics and AOMs are less well-elucidated. In this review, the recent research proceedings on cometabolic biodegradation of antibiotics by AOMs were summarized. Ammonia oxidizing bacteria (AOB), ammonia oxidizing archaea (AOA) and complete ammonia oxidizers (comammox) played significant roles in both nitrification and cometabolic biodegradation of antibiotics. Antibiotics at varying concentrations might pose inhibiting or stimulating effect on AOMs, influencing the microbial activity, community abundance and ammonia monooxygenase subunit A gene expression level. AOMs-induced cometabolic biodegradation products were analyzed as well as the corresponding pathways for each type of antibiotics. The effects of ammonium availability, initial antibiotic concentration, sludge retention time and temperature were assessed on the cometabolic biodegradation efficiencies of antibiotics. This work might provide further insights into the fate and removal of antibiotics during nitrification processes.

Comparison of chemical and biological degradation of sulfonamides: Solving the mystery of sulfonamide transformation

Sulfonamides (SAs) are widespread in aquatic environments and pose serious environmental risks. The removal efficiencies and degradation mechanisms of SAs in both chemical and biological degradation systems were comprehensively reviewed. Density functional theory (DFT) was utilized to decipher the reaction types and reactive sites of both degradation mechanisms at the electron level. In chemical degradation, the rate of the reactive oxidants to degrade SAs follows the order SO₄•^- ≈ •OH > O₃ > ¹O₂ > ClO₂ ≈ Fe(VI) ≈ HOCl > peroxymonosulfate. pH affects the oxidation-reduction potentials of oxidants, the reactivity of SAs, and the intermolecular force between oxidants and SAs, thereby affecting the chemical degradation efficiencies and mechanisms. In biological degradation, oxidoreductase produced by bacteria, fungi, algae, and plants can degrade SAs. The catalytic activity of the enzyme is affected by the enzyme system, reaction conditions, and type of SAs. Despite the different reaction modes and removal efficiencies of SAs in chemical degradation and biological degradation, the transformation pathways and products show commonalities. Modification of the amino (N¹H₂-) moiety and destruction of sulfonamide bridge (-SO₂-N¹¹H-) moiety are the main pathways for both chemical and biological degradation of SAs. Most oxidants or enzymes can react with the N¹H₂- moiety. Reactions of the -SO₂-N¹¹H- moiety are mainly initiated by the cleavage of S-N bonds for five-membered heterocyclic ring-substituted SAs, and by SO₂ extrusion for six-membered heterocyclic ring-substituted SAs. Chlorine substitution and coupling on the N¹H₂- moiety, hydroxylation of the benzene moiety, oxidation of methyl, and isomerization of the R substituents are the transformation pathways unique to chemical degradation. Formylation/acetylation, glycosylation, pterin conjugation, and deamination of the N¹H₂- moiety are the transformation pathways unique to biological degradation. DFT studies revealed the same reaction types and the same reactive sites of SAs in chemical and biological degradation. Electrophiles are mostly prone to attack the N¹ atom on the amino moiety of neutral SAs and the N¹¹ atom on the sulfonamide bridge moiety of anionic SAs, leading to nitration or electrophilic substitution of the amino moiety and the cleavage of S-N bonds or SO₂ extrusion of the sulfonamide bridge moiety. Reactions on the -SO₂-N¹¹H- moiety eliminate antibacterial activity in the SA degradation process. This review elucidated SA transformation by comparing the chemical and biological degradation of SAs. This could provide theoretical guidance for the development of more efficient and economical treatment technologies for SAs.

Effect of pig manure-derived sulfadiazine on species distribution and bioactivities of soil ammonia-oxidizing microorganisms after fertilization

To evaluate the effect of pig manure-derived sulfadiazine (SDZ) on the species distribution and bioactivities of ammonia-oxidizing microorganisms (AOMs), ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA) and complete ammonia oxidizer (comammox) within the soil were investigated pre- and post-fertilization. Kinetic modeling and linear regression results demonstrated that the DT₅₀ value of different SDZ fractions under initial SDZ concentrations of 50 and 100 mg·kg^-1 exhibited the following trend: total SDZ>CaCl₂-extractable SDZ>MeOH-extractable SDZ, whereas their inhibiting effect on AOMs showed an opposite trend. qPCR analysis suggested that comammox was the predominant ammonia oxidizer in soils regardless of SDZ addition, accounting for as much as 77.2-94.7% of the total amoA, followed by AOA (5.3-22.5%), whereas AOB (<0.5%) was the lowest. The SDZ exhibited a significant effect on the AOM abundance. Specifically, SDZ exerted the highest inhibitory effect on comammox growth, followed by AOA, whereas negligible for AOB. The community diversity of AOMs within the pig manure-fertilized soils was affected by SDZ, and AOA Nitrososphaera cluster 3 played a key role in potential ammonia oxidation capacity (PAO) maintenance. This study provides new insights into the inhibition mechanisms of pig manure-derived antibiotics on AOMs within the fertilized soil.

Enzymatic cometabolic biotransformation of organic micropollutants in wastewater treatment plants: A review

Biotransformation of trace-level organic micropollutants (OMPs) by complex microbial communities in wastewater treatment facilities is a key process for their detoxification and environmental impact reduction. Therefore, understanding the metabolic activities and mechanisms that contribute to their biotransformation is essential when developing approaches aiming to minimize their discharge. This review addresses the relevance of cometabolic processes and discusses the main enzymatic activities currently known to take part in OMPs removal under different redox environments in the compartments of wastewater treatment plants. Furthermore, the most common methodologies to decipher such enzymes are discussed, including the use of in vitro enzyme assays, enzymatic inhibitors, the analysis of transformation products and the application of several -omic techniques. Finally, perspectives on major challenges and future research requirements to improve OMPs biotransformation are proposed.

Enhanced biodegradation of ciprofloxacin by enriched nitrifying sludge: assessment of removal pathways and microbial responses

Antibiotics are mostly collected by sewage systems, but not completely removed within wastewater treatment plants. Their release to aquatic environment poses a great threat to public health. This study evaluated the removal of a widely used fluoroquinolone antibiotic, ciprofloxacin, in enriched nitrifying culture through a series of experiments by controlling ammonium concentrations and inhibiting functional microorganisms. The removal efficiency of ciprofloxacin at an initial concentration of 50 μg L^-1 reached 81.86 ± 3.21% in the presence of ammonium, while only 22.83 ± 8.22% of ciprofloxacin was removed in its absence. A positive linear correlation was found between the ammonia oxidation rate (AOR) and ciprofloxacin biodegradation rate. These jointly confirmed the importance of the AOB-induced cometabolism in ciprofloxacin biodegradation, with adsorption and metabolic degradation pathways playing minor roles. The continuous exposure of AOB to ciprofloxacin led to decreases of ammonia monooxygenase (AMO) activities and AOR. The antibacterial effects of ciprofloxacin and its biodegradation products were further evaluated and the results revealed that biodegradation products of ciprofloxacin exhibited less toxicity compared to the parent compound, implying the potential application of cometabolism in alleviation of antimicrobial activity. The findings provided new insights into the AOB-induced cometabolic biodegradation of fluoroquinolone antibiotics.

Quantifying the contribution rates of sulfonamide antibiotics removal mechanisms in constructed wetlands using multivariate statistical analysis

The removal of antibiotics in subsurface flow constructed wetlands is performed through various removal mechanisms, such as adsorption, hydrolysis, microbial degradation and plant uptake. However, the contribution rates of the removal mechanisms in constructed wetlands are still not well studied. This study conducted a series of experiments and used multivariate statistical analysis to determine contribution rates for substrate adsorption, hydrolysis, and microbial degradation. Multiple stepwise regression analysis indicated that specific surface area and salt content were the main factors influencing sulfonamide adsorption, while temperature and pH were the main factors influencing sulfonamide hydrolysis. Variance partitioning analysis showed that the influence of physical-chemical factors was greater than that of nutrients on the microbial community. Partial least squares path analysis showed that the path coefficients of microbial degradation, adsorption and hydrolysis for sulfonamides removal in vertical subsurface flow constructed wetlands were 0.6339, 0.3608 and 0.0351, respectively, while the corresponding path coefficient were 0.5658, 0.4707 and 0.1079 in horizontal subsurface flow constructed wetlands, respectively. This means that microbial degradation contributes the most to the removal of sulfonamides in subsurface flow constructed wetlands. Enhanced microbial degradation may be a powerful measure to improve the removal of sulfonamides. These results will be helpful for understanding the removal mechanism of antibiotics and will provide a definite direction for pertinently improving sulfonamide removal efficiency in constructed wetlands.

A Review of Ammonia-Oxidizing Archaea and Anaerobic Ammonia-Oxidizing Bacteria in the Aquaculture Pond Environment in China

The excessive ammonia produced in pond aquaculture processes cannot be ignored. In this review, we present the distribution and diversity of ammonia-oxidizing archaea (AOA) and anaerobic ammonia-oxidizing bacteria (AnAOB) in the pond environment. Combined with environmental conditions, we analyze the advantages of AOA and AnAOB in aquaculture water treatment and discuss the current situation of pond water treatment engineering involving these microbes. AOA and AnAOB play an important role in the nitrogen removal process of aquaculture pond water, especially in seasonal low temperatures and anoxic sediment layers. Finally, we prospect the application of bioreactors to purify pond aquaculture water using AOA and AnAOB, in autotrophic nitrogen removal, which can reduce the production of greenhouse gases (such as nitrous oxide) and is conducive to the development of environmentally sustainable pond aquaculture.