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

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.

Effect of calcium peroxide pretreatment on the remediation of sulfonamide antibiotics (SMs) by Chlorella sp

This study investigated the effect of CaO₂ pretreatment on sulfonamide antibiotics (SMs) remediation by Chlorella sp. Results showed that a CaO₂ dose ranging from 0.05 to 0.1 g/g biomass was the best and led to higher SMs removal efficacy 5-10% higher than the control. The contributions made by cometabolism and CaO₂ in SMs remediation were very similar. Bioassimilation could remove 24% of sulfadiazine (SDZ) and sulfamethazine (SMZ), and accounted for 38% of sulfamethoxazole (SMX) remediation. Pretreatment by CaO₂ wielded a positive effect on microalgae. The extracellular polymeric substances (EPS) level of the CaO₂ pretreatment microalgae was three times higher when subjected to non-pretreatment. For the long-term, pretreatment microalgae removed SMs 10-20% more than the non-pretreatment microalgae. Protein fractions of EPS in continuous operation produced up to 90 mg/L for cometabolism. For bioassimilation, SMX intensity of the pretreatment samples was 160-fold less than the non-treatment one. It indicated the CaO₂ pretreatment has enhanced the biochemical function of the intracellular environment of microalgae. Peroxidase enzyme involved positively in the cometabolism and degradation of SMs to several metabolites including ring cleavage, hydroxylation and pterin-related conjugation.

Microbiome assembly for sulfonamide subsistence and the transfer of genetic determinants

Antibiotic subsistence in bacteria represents an alternative resistance machinery, while paradoxically, it is also a cure for environmental resistance. Antibiotic-subsisting bacteria can detoxify antibiotic-polluted environments and prevent the development of antibiotic resistance in environments. However, progress toward efficient in situ engineering of antibiotic-subsisting bacteria is hindered by the lack of mechanistic and predictive understanding of the assembly of the functioning microbiome. By top-down manipulation of wastewater microbiomes using sulfadiazine as the single limiting source, we monitored the ecological selection process that forces the wastewater microbiome to perform efficient sulfadiazine subsistence. We found that the community-level assembly selects for the same three families rising to prominence across different initial pools of microbiomes. We further analyzed the assembly patterns using a linear model. Detailed inspections of the sulfonamide metabolic gene clusters in individual genomes of isolates and assembled metagenomes reveal limited transfer potential beyond the boundaries of the Micrococcaceae lineage. Our results open up new possibilities for engineering specialist bacteria for environmental applications.

Biotransformation of Doxorubicin Promotes Resilience in Simplified Intestinal Microbial Communities

Chemotherapeutic drugs can cause harmful gastrointestinal side effects, which may be modulated by naturally occurring members of our microbiome. We constructed simplified gut-associated microbial communities to test the hypothesis that bacteria-mediated detoxification of doxorubicin (i.e., a widely used chemotherapeutic) confers protective effects on the human microbiota. Mock communities composed of up to five specific members predicted by genomic analysis to be sensitive to the drug or resistant via biotransformation and/or efflux were grown in vitro over three generational stages to characterize community assembly, response to perturbation (doxorubicin exposure), and resilience. Bacterial growth and drug concentrations were monitored with spectrophotometric assays, and strain relative abundances were evaluated with 16S rRNA gene sequencing. Bacteria with predicted resistance involving biotransformation significantly lowered concentrations of doxorubicin in culture media, permitting growth of drug-sensitive strains in monoculture. Such protective effects were not produced by strains with drug resistance conferred solely by efflux. In the mixed communities, resilience of drug-sensitive members depended on the presence and efficiency of transformers, as well as drug exposure concentration. Fitness of bacteria that were resistant to doxorubicin via efflux, though not transformation, also improved when the transformers were present. Our simplified community uncovered ecological relationships among a dynamic consortium and highlighted drug detoxification by a keystone species. This work may be extended to advance probiotic development that may provide gut-specific protection to patients undergoing cancer treatment. IMPORTANCE While chemotherapy is an essential intervention for treating many forms of cancer, gastrointestinal side effects may precede infections and risks for additional health complications. We developed an in vitro model to characterize key changes in bacterial community dynamics under chemotherapeutic stress and the role of bacterial interactions in drug detoxification to promote microbiota resilience. Our findings have implications for developing bio-based strategies to promote gut health during cancer treatment.

Biotransformation of lincomycin and fluoroquinolone antibiotics by the ammonia oxidizers AOA, AOB and comammox: A comparison of removal, pathways, and mechanisms

In this study, we evaluated the biotransformation mechanisms of lincomycin (LIN) and three fluoroquinolone antibiotics (FQs), ciprofloxacin (CFX), norfloxacin (NFX), and ofloxacin (OFX), which regularly enter aquatic environments through human activities, by different ammonia-oxidizing microorganisms (AOM). The organisms included a pure culture of the complete ammonia oxidizer (comammox) Nitrospira inopinata, an ammonia oxidizing archaeon (AOA) Nitrososphaera gargensis, and an ammonia-oxidizing bacterium (AOB) Nitrosomonas nitrosa Nm90. The removal of these antibiotics by the pure microbial cultures and the protein-normalized biotransformation rate constants indicated that LIN was significantly co-metabolically biotransformed by AOA and comammox, but not by AOB. CFX and NFX were significantly co-metabolized by AOA and AOB, but not by comammox. None of the tested cultures transformed OFX effectively. Generally, AOA showed the best biotransformation capability for LIN and FQs, followed by comammox and AOB. The transformation products and their related biotransformation mechanisms were also elucidated. i) The AOA performed hydroxylation, S-oxidation, and demethylation of LIN, as well as nitrosation and cleavage of the piperazine moiety of CFX and NFX; ii) the AOB utilized nitrosation to biotransform CFX and NFX; and iii) the comammox carried out hydroxylation, demethylation, and demethylthioation of LIN. Hydroxylamine, an intermediate of ammonia oxidation, chemically reacted with LIN and the selected FQs, with removals exceeding 90%. Collectively, these findings provide important fundamental insights into the roles of different ammonia oxidizers and their intermediates on LIN and FQ biotransformation in nitrifying environments including wastewater treatment systems.

Antibiotics in wastewater: From its occurrence to the biological removal by environmentally conscious technologies

In this critical review, we explored the most recent advances about the fate of antibiotics on biological wastewater treatment plants (WWTP). Although the occurrence of these pollutants in wastewater and natural streams has been investigated previously, some recent publications still expose the need to improve the detection strategies and the lack of information about their transformation products. The role of the antibiotic properties and the process operating conditions were also analyzed. The pieces of evidence in the literature associate several molecular properties to the antibiotic removal pathway, like hydrophobicity, chemical structure, and electrostatic interactions. Nonetheless, the influence of operating conditions is still unclear, and solid retention time stands out as a key factor. Additionally, the efficiencies and pathways of antibiotic removals on conventional (activated sludge, membrane bioreactor, anaerobic digestion, and nitrogen removal) and emerging bioprocesses (bioelectrochemical systems, fungi, and enzymes) were assessed, and our concern about potential research gaps was raised. The combination of different bioprocess can efficiently mitigate the impacts generated by these pollutants. Thus, to plan and design a process to remove and mineralize antibiotics from wastewater, all aspects must be addressed, the pollutant and process characteristics and how it is the best way to operate it to reduce the impact of antibiotics in the environment.

Role of Ammonia Oxidation in Organic Micropollutant Transformation during Wastewater Treatment: Insights from Molecular, Cellular, and Community Level Observations

Organic micropollutants (OMPs) are a threat to aquatic environments, and wastewater treatment plants may act as a source or a barrier of OMPs entering the environment. Understanding the fate of OMPs in wastewater treatment processes is needed to establish efficient OMP removal strategies. Enhanced OMP biotransformation has been documented during biological nitrogen removal and has been attributed to the cometabolic activity of ammonia-oxidizing bacteria (AOB) and, specifically, to the ammonia monooxygenase (AMO) enzyme. Yet, the exact mechanisms of OMP biotransformation are often unknown. This critical review aims to fundamentally and quantitatively evaluate the role of ammonia oxidation in OMP biotransformation during wastewater treatment processes. OMPs can be transformed by AOB via direct and indirect enzymatic reactions: AMO directly transforms OMPs primarily via hydroxylation, while biologically produced reactive nitrogen species (hydroxylamine (NH₂OH), nitrite (NO₂^-), and nitric oxide (NO)) can chemically transform OMPs through nitration, hydroxylation, and deamination and can contribute significantly to the observed OMP transformations. OMPs containing alkyl, aliphatic hydroxyl, ether, and sulfide functional groups as well as substituted aromatic rings and aromatic primary amines can be biotransformed by AMO, while OMPs containing alkyl groups, phenols, secondary amines, and aromatic primary amines can undergo abiotic transformations mediated by reactive nitrogen species. Higher OMP biotransformation efficiencies and rates are obtained in AOB-dominant microbial communities, especially in autotrophic reactors performing nitrification or nitritation, than in non-AOB-dominant microbial communities. The biotransformations of OMPs in wastewater treatment systems can often be linked to ammonium (NH₄⁺) removal following two central lines of evidence: (i) Similar transformation products (i.e., hydroxylated, nitrated, and desaminated TPs) are detected in wastewater treatment systems as in AOB pure cultures. (ii) Consistency in OMP biotransformation (r_bio, μmol/g VSS/d) to NH₄⁺ removal (r_NH4+, mol/g VSS/d) rate ratios (r_bio/r_NH4+) is observed for individual OMPs across different systems with similar r_NH4+ and AOB abundances. In this review, we conclude that AOB are the main drivers of OMP biotransformation during wastewater treatment processes. The importance of biologically driven abiotic OMP transformation is quantitatively assessed, and functional groups susceptible to transformations by AMO and reactive nitrogen species are systematically classified. This critical review will improve the prediction of OMP transformation and facilitate the design of efficient OMP removal strategies during wastewater treatment.

Impact of intermittent feeding on polishing of micropollutants by moving bed biofilm reactors (MBBR)

Moving bed biofilm reactors (MBBRs) were placed at two wastewater treatment plants, where they were constantly fed with effluent and intermittently fed with primary wastewater. Each reactor was subjected to different feast/famine periods and flow rates of primary wastewater, thus the different organic and nutrient loads (chemical oxygen demand(COD), ammonium(NH4-N)) resulted in different feast-famine conditions applied to the biomass. In batch experiments, this study investigated the effects of various feast-famine conditions on the biodegradation of micropollutants by MBBRs applied as an effluent polishing step. Rate constants of micropollutant removals were found to be positively correlated to the load of the total COD and NH4-N, indicating that higher organic loads were favourable for the growth of micropollutant degraders in these MBBRs. Rate constant of atenolol was five times higher when the biomass was fed with the highest COD and NH4-N load than it was fed with the lowest COD and NH4-N load. For diclofenac, mycophenolic acid and iohexol, their maximum rate constants were obtained with feeding of COD and NH4-N of approximately 570 mgCOD/d and 40∼60 mgNH4-N/d respectively. This also supports the concept that co-metabolism (rather competition inhibition or catabolic repression) plays an important role in micropollutants biodegradation in wastewater.

Removal of pharmaceuticals by ammonia oxidizers during nitrification

The adverse effect of pharmaceuticals on ecosystem and human health raises great interest for the removal of pharmaceuticals in wastewater treatment plants (WWTPs). Enhanced removal of pharmaceuticals by ammonia oxidizers (AOs) has been observed during nitrification. This review provides a comprehensive summary on the removal of pharmaceuticals by AOs-ammonia oxidizing bacteria (AOB), ammonia oxidizing archaea (AOA), and complete ammonia oxidizer (comammox) during nitrification in pure ammonia oxidizing culture and mixed microbes systems. The superior removal of pharmaceuticals by AOs in conditions with nitrifying activity compared with the conditions without nitrifying activity was proposed. The contribution of AOs on pharmaceuticals removal in pure and mixed microbe systems was discussed and activated sludge modeling was suggested as the proper measure on assessing the contribution of AOs on the removal of pharmaceuticals in mixed microbe culture. Three transformation processes and the involved reaction types of pharmaceuticals transformation during nitrification were reviewed. The present paper provides a systematical summary on pharmaceuticals removal by different AOs across pure and mixed microbes culture during nitrification, which opens up the opportunity to optimize the wastewater biological treatment systems for enhanced removal of pharmaceuticals. KEY POINTS: • The superior removal of pharmaceuticals by ammonia oxidizers (AOs) was summarized. • The removal contribution of pharmaceuticals attributed by AOs was elucidated. • The transformation processes and reaction types of pharmaceuticals were discussed.

Enhanced removal of cephalexin and sulfadiazine in nitrifying membrane-aerated biofilm reactors

Nitrification process has been reported to be capable of degrading various pharmaceuticals due to the cometabolism of ammonia-oxidizing bacteria (AOB). The membrane aerated biofilm reactor (MABR) is an emerging configuration in wastewater treatment with advantages of high nitrification rate and low energy consumption. However, there are very few studies investigating the degradation of antibiotics at environmentally relevant levels in nitrifying MABR systems. In this study, the removal of two widely used antibiotics, cephalexin (CFX) and sulfadiazine (SDZ), was evaluated in two independent MABRs with nitrifying biofilms. The impacts of CFX and SDZ exposure on the nitrification performance and microbial community structure within biofilms were also investigated. The results showed that nitrifying biofilms were very efficient in removing CFX (94.6%) and SDZ (75.4%) with an initial concentration of 100 μg/L when hydraulic retention time (HRT) was 4 h in the reactors. When HRT decreased from 4 h to 3 h, the removal rates of CFX and SDZ increased significantly from 23.4 ± 1.0 μg/(L·h) and 18.7 ± 1.1 μg/(L·h), respectively, to 27.7 ± 1.3 μg/(L·h) (p＜0.01) and 20.8 ± 2.4 μg/(L·h) (p＜0.05), while the removal efficiencies decreased to 86.0% and 61.5%, respectively. Despite the exposure to CFX and SDZ, the nitrification performance was not affected, and microbial community structure within biofilms also remained relatively stable. This study shows that nitrifying MABR process is a promising option for the efficient removal of antibiotics from domestic wastewater.

Microbial Cleavage of C-F Bonds in Two C6 Per- and Polyfluorinated Compounds via Reductive Defluorination

The C-F bond is one of the strongest single bonds in nature. Although microbial reductive dehalogenation is well known for the other organohalides, no microbial reductive defluorination has been documented for perfluorinated compounds except for a single, nonreproducible study on trifluoroacetate. Here, we report on C-F bond cleavage in two C₆ per- and polyfluorinated compounds via reductive defluorination by an organohalide-respiring microbial community. The reductive defluorination was demonstrated by the release of F^- and the formation of the corresponding product when lactate was the electron donor, and the fluorinated compound was the sole electron acceptor. The major dechlorinating species in the seed culture, Dehalococcoides, were not responsible for the defluorination as no growth of Dehalococcoides or active expression of Dehalococcoides-reductive dehalogenases was observed. It suggests that minor phylogenetic groups in the community might be responsible for the reductive defluorination. These findings expand our fundamental knowledge of microbial reductive dehalogenation and warrant further studies on the enrichment, identification, and isolation of responsible microorganisms and enzymes. Given the wide use and emerging concerns of fluorinated organics (e.g., per- and polyfluoroalkyl substances), particularly the perfluorinated ones, the discovery of microbial defluorination under common anaerobic conditions may provide valuable insights into the environmental fate and potential bioremediation strategies of these notorious contaminants.

Living with sulfonamides: a diverse range of mechanisms observed in bacteria

Sulfonamides are the oldest class of synthetic antibiotics still in use in clinical and veterinary settings. The intensive utilization of sulfonamides has been leading to the widespread contamination of the environment with these xenobiotic compounds. Consequently, in addition to pathogens and commensals, also bacteria inhabiting a wide diversity of environmental compartments have been in contact with sulfonamides for almost 90 years. This review aims at giving an overview of the effect of sulfonamides on bacterial cells, including the strategies used by bacteria to cope with these bacteriostatic agents. These include mechanisms of antibiotic resistance, co-metabolic transformation, and partial or total mineralization of sulfonamides. Possible implications of these mechanisms on the ecosystems and dissemination of antibiotic resistance are also discussed. KEY POINTS: • Sulfonamides are widespread xenobiotic pollutants; • Target alteration is the main sulfonamide resistance mechanism observed in bacteria; • Sulfonamides can be modified, degraded, or used as nutrients by some bacteria.

A refined set of rRNA-targeted oligonucleotide probes for in situ detection and quantification of ammonia-oxidizing bacteria

Ammonia-oxidizing bacteria (AOB) of the betaproteobacterial genera Nitrosomonas and Nitrosospira are key nitrifying microorganisms in many natural and engineered ecosystems. Since many AOB remain uncultured, fluorescence in situ hybridization (FISH) with rRNA-targeted oligonucleotide probes has been one of the most widely used approaches to study the community composition, abundance, and other features of AOB directly in environmental samples. However, the established and widely used AOB-specific 16S rRNA-targeted FISH probes were designed up to two decades ago, based on much smaller rRNA gene sequence datasets than available today. Several of these probes cover their target AOB lineages incompletely and suffer from a weak target specificity, which causes cross-hybridization of probes that should detect different AOB lineages. Here, a set of new highly specific 16S rRNA-targeted oligonucleotide probes was developed and experimentally evaluated that complements the existing probes and enables the specific detection and differentiation of the known, major phylogenetic clusters of betaproteobacterial AOB. The new probes were successfully applied to visualize and quantify AOB in activated sludge and biofilm samples from seven pilot- and full-scale wastewater treatment systems. Based on its improved target group coverage and specificity, the refined probe set will facilitate future in situ analyses of AOB.

Municipal wastewater treatment targeting pharmaceuticals by a pilot-scale hybrid attached biofilm and activated sludge system (Hybas™)

A hybrid wastewater treatment process with combined attached biofilm (moving bed biofilm reactor) and activated sludge, named as Hybas™, was implemented for the treatment of municipal wastewater. The system consisted of six staged reactors in series including pre-denitrification and nitrification in the Hybas™ line and post-denitrification in a pure MBBR. In addition to the significant removal of nutrients and organic matter from municipal wastewater, Hybas™ also showed removal capacity for pharmaceuticals. Of particular interest was the enhanced removal for pharmaceuticals (i.e. X-ray contrast media) compared to other biological systems. Spiking experiments showed that the maximum removal rate constants (k, h^-1) for 10 out of the 21 investigated pharmaceuticals (including diclofenac) were observed to occur within the two aerobic Hybas ™ reactors, operated in a flow-shifting mode that allows even biofilm growth of nitrifying bacteria. In total, 14 out of the 21 pharmaceuticals were removed by more than 50% during continuous flow operation in the all Hybas™ line and post-denitrification MBBR. The calculated and estimated removal contributions of pharmaceuticals by each individual reactor were also assessed.

Comparison of diclofenac transformation in enriched nitrifying sludge and heterotrophic sludge: Transformation rate, pathway, and role exploration

The adverse effects of diclofenac (DCF) on ecosystems and human health have induced increasing interest in its elimination in environment. DCF can be removed to some extent by nitrifying and heterotrophic microbes during wastewater treatment process. However, the actual roles of nitrifying and heterotrophic microbes in the transformation of DCF remain unclear. In this study, batch experiments were conducted to explore the biological transformation of DCF in enriched nitrifying sludge (NS), heterotrophic sludge (HS) and activated sludge (AS) systems. DCF was removed three times faster in enriched NS than in HS. Three transformation pathways of DCF in enriched NS, HS, and AS were proposed and compared. Hydroxylation was the crucial transformation step in the three transformation pathways. A faster hydroxylation reaction contributed to the faster removal of DCF in enriched NS. More transformation products (TPs) and reaction types (i.e. reductive dechlorination, sulphidation and methylation reactions) were observed in HS. Furthermore, some TPs that were resistant to degrade in enriched NS, such as DCF-benzoic acid, could be further transformed in HS. Accordingly, enriched NS could remove DCF more rapidly while HS could further transform some TPs resistant to degrade in enriched NS. Nitrifying and heterotrophic microbes may cooperatively and rapidly eliminate not only DCF, but also its TPs.

Achieving simultaneous nitrogen and antibiotic removal in one-stage partial nitritation-Anammox (PN/A) process

Partial nitritation-Anammox (PN/A) process has been recognized as a sustainable process for biological nitrogen removal. Although various antibiotics have been ubiquitously detected in influent of wastewater treatment plants, little is known whether functional microorganisms in the PN/A process are capable of biodegrading antibiotics. This study aimed to investigate simultaneous nitrogen and antibiotic removal in a lab-scale one-stage PN/A system treating synthetic wastewater containing a widely-used antibiotic, sulfadiazine (SDZ). Results showed that maximum total nitrogen (TN) removal efficiency of 86.1% and SDZ removal efficiency of 95.1% could be achieved when treating 5 mg/L SDZ under DO conditions of 0.5-0.6 mg/L. Compared to anammox bacteria, ammonia-oxidizing bacteria (AOB) made a major contribution to SDZ degradation through their cometabolic pathway. A strong correlation between amoA gene and SDZ removal efficiency was found (p < 0.01). In addition, the degradation products of SDZ did not exhibit any inhibitory effects on Escherichia coli. The findings suggest that it is promising to apply the PN/A process to simultaneously remove antibiotics and nitrogen from contaminated wastewater.

Insitu kinetics of human pharmaceutical conjugates and the impact of transformation, deconjugation, and sorption on persistence in wastewater batch bioreactors

The fate of selected common pharmaceuticals and four of their major conjugates in wastewater batch bioreactors was evaluated to determine how treatment plant parameters such as addition of air, and the presence of waste activated sludge (WAS) could influence the removal of parent compounds and conjugates. Under a realistic hydraulic residence time (HRT) for each treatment sub-process of approximately 2 h, acetaminophen and its sulfate metabolite were both rapidly degraded (>99%). Propranolol was sulfated and concurrently removed. Deconjugation of N-acetylsulfamethoxazole and sulfamethoxazole-glucuronide contributed to increases of the parent sulfamethoxazole. Thyroxine was resistant to degradation, while thyroxine-glucuronide was rapidly deconjugated (>90% in <2 h). In the absence of WAS, sorption to suspended solids was another major removal mechanism for acetaminophen, propranolol, sulfamethoxazole, and thyroxine. However, with WAS, concentrations associated with suspended solids decreased for all analytes within 24 h. These results indicate that both conjugation and back-transformation are compound-specific and dependent on parameters such as HRT, addition of microbial content, and suspended solids levels. Therefore, conjugation-deconjugation processes may strongly influence the speciation of pharmaceuticals and their fate in wastewater treatment plant effluents.

Micropollutants cometabolism of microalgae for wastewater remediation: Effect of carbon sources to cometabolism and degradation products

This study investigated the impacts of selective sole carbon source-induced micropollutants (MPs) cometabolism of Chlorella sp. by: (i) extracellular polymeric substances (EPS), superoxide dismutase and peroxidase enzyme production; (ii) MPs removal efficiency and cometabolism rate; (iii) MPs' potential degradation products identification; and (iv) degradation pathways and validation using the Eawag database to differentiate the cometabolism of Chlorella sp. with other microbes. Adding the sole carbon sources in the presence of MPs increased EPS and enzyme concentrations from 2 to 100-fold in comparison with only sole carbon sources. This confirmed that MPs cometabolism had occurred. The removal efficiencies of tetracycline, sulfamethoxazole, and bisphenol A ranged from 16-99%, 32-92%, and 58-99%, respectively. By increasing EPS and enzyme activity, the MPs concentrations accumulated in microalgae cells also fell 400-fold. The cometabolism process resulted in several degradation products of MPs. This study drew an insightful understanding of cometabolism for MPs remediation in wastewater. Based on the results, proper carbon sources for microalgae can be selected for practical applications to remediate MPs in wastewater while simultaneously recovering biomass for several industries and gaining revenue.

Degradation and transformation of nitrated nonylphenol isomers in activated sludge under nitrifying and heterotrophic conditions

Nitrated nonylphenols (2-nitro-nonylphenols, NNPs) are metabolites of the endocrine-disrupter nonylphenols (NPs). While they have been detected in the environment, their fate in activated sludge has yet to be determined. In this study, we used synthesized NNP isomers and a ¹⁴C-tracer technique to study the degradation and transformation of four NNP isomers (NNP₁₁₁, NNP₁₁₂, NNP₃₈, and NNP₆₅) in nitrifying activated sludge (NAS) and heterotrophic bacteria-enhanced activated sludge (HAS). Our results showed that the degradation of NNPs in both NAS and HAS was isomer-specific. The half-lives of the NNPs decreased in the order: NNP₁₁₁ > NNP₁₁₂ > NNP₃₈ > NNP₆₅. After 36 days of incubation, 9.48 % and 4.01 % of the ¹⁴C-NNP₁₁₁ was mineralized in NAS and HAS, respectively. In addition to mineralization, five metabolites of NNPs containing hydroxyl, carbonyl, and carboxyl substituents on the alkyl chains were formed in NAS but not in HAS. The transformation of NNPs differed in NAS and HAS, mainly due to the differences in their microbial communities and the activities thereof in NAS and HAS. This is the first study of the isomer-specific fate of NNP isomers in activated sludge. Future studies should assess the toxicity, stability and potential risks of NNP metabolites in the environment.

Unravelling kinetic and microbial responses of enriched nitrifying sludge under long-term exposure of cephalexin and sulfadiazine

Wastewater treatment plants (WWTPs) have been identified as one of the reservoirs of antibiotics. Although nitrifying bacteria have been reported to be capable of degrading various antibiotics, there are very few studies investigating long-term effects of antibiotics on kinetic and microbial responses of nitrifying bacteria. In this study, cephalexin (CFX) and sulfadiazine (SDZ) were selected to assess chronic impacts on nitrifying sludge with stepwise increasing concentrations in two independent bioreactors. The results showed that CFX and SDZ at an initial concentration of 100 μg/L could be efficiently removed by enriched nitrifying sludge, as evidenced by removal efficiencies of more than 88% and 85%, respectively. Ammonia-oxidizing bacteria (AOB) made a major contribution to the biodegradation of CFX and SDZ via cometabolism, compared to limited contributions from heterotrophic bacteria and nitrite-oxidizing bacteria. Chronic exposure to CFX (≥30 μg/L) could stimulate ammonium oxidation activity in terms of a significant enhancement of ammonium oxidation rate (p < 0.01). In contrast, the ammonium oxidation activity was inhibited due to exposure to 30 μg/L SDZ (p < 0.01), then it recovered after long-term adaption under exposure to 50 and 100 μg/L SDZ. In addition, 16S rRNA gene amplicon sequencing revealed that the relative abundance of AOB decreased distinctly from 23.8% to 28.8% in the control phase (without CFX or SDZ) to 14.2% and 10.8% under exposure to 100 μg/L CFX and SDZ, respectively. However, the expression level of amoA gene was up-regulated to overcome this adverse impact and maintain a stable and efficient removal of both ammonium and antibiotics. The findings in this study shed a light on chronic effects of antibiotic exposure on kinetic and microbial responses of enriched nitrifying sludge in WWTPs.

Specific Micropollutant Biotransformation Pattern by the Comammox Bacterium Nitrospira inopinata

The recently discovered complete ammonia-oxidizing (comammox) bacteria occur in various environments, including wastewater treatment plants. To better understand their role in micropollutant biotransformation in comparison with ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA), we investigated the biotransformation capability of Nitrospira inopinata (the only comammox isolate) for 17 micropollutants. Asulam, fenhexamid, mianserin, and ranitidine were biotransformed by N. inopinata, Nitrososphaera gargensis (AOA), and Nitrosomonas nitrosa Nm90 (AOB). More distinctively, carbendazim, a benzimidazole fungicide, was exclusively biotransformed by N. inopinata. The biotransformation of carbendazim only occurred when N. inopinata was supplied with ammonia but not nitrite as the energy source. The exclusive biotransformation of carbendazim by N. inopinata was likely enabled by an enhanced substrate promiscuity of its unique AMO and its much higher substrate (for ammonia) affinity compared with the other two ammonia oxidizers. One major plausible transformation product (TP) of carbendazim is a hydroxylated form at the aromatic ring, which is consistent with the function of AMO. These findings provide fundamental knowledge on the micropollutant degradation potential of a comammox bacterium to better understand the fate of micropollutants in nitrifying environments.