Responses of anammox to long-term p-nitrophenol stress: From apparent and microscopic phenomena to mechanism simulation

Transcriptional and molecular simulation analysis of the response mechanism of anammox bacteria to 3,4-dimethylpyrazole phosphate stress

Anaerobic ammonium oxidation (anammox) and nitrification are two vital biological pathways for ammonium oxidation, pivotal in microbial nitrogen cycling. 3,4-Dimethylpyrazole phosphate (DMPP) is commonly used as inhibitors in agricultural soils to reduce nitrogen losses from farmland, while whether it affect anammox is an open question. Acute inhibition tests revealed that 53.5 mg·L-1 DMPP caused 50 % reduction in anammox bacteria. After 36 days of prolonged exposure to 5 mg·L-1 DMPP, the ammonium(nitrite) removal rate of endnote decreased from 78.39(94.78) to 13.57(15.28) mgN·gVSS-1·d-1. Additionally, the abundance of Ca. Kuenenia decreased from 36.5 % to 6.06 %. Transcriptomic analysis revealed that the mRNA levels of ammonium transport genes (amt_1 and amt_4), and hydrazine synthase (hzs) were significantly downregulated. Molecular docking simulations indicated that DMPP bound with ammonium transport and hydrazine synthesis. This interaction hindered the transcriptional levels of genes encoding ammonium transporters and hzs. The study has guiding value to reduce the nitrogen loss involved in anammox bacteria in agricultural soils under the application of DMPP.

KOH-modified biochar enhances nitrogen metabolism of the chloroquine phosphate-disturbed anammox: Physical binding, EPS modulation and versatile metabolic hierarchy

Chloroquine phosphate (CQ) poses strong biotoxicity on anammox process, and thus detoxifying is essential for the stable operation of anammox in treating CQ-bearing wastewater. Biochar has been proven to simultaneously detoxify pollutant and modulate nitrogen cycle in anammox by its shelter effect and electron exchange capacity (EEC) ability. To further improve the ability of biochar to promote the nitrogen metabolism of anammox, a KOH modification strategy was used to tailor a high-EEC biochar in this work. KOH modified biochar can bind CQ for detoxification driven by hydrogen bond, π-π interaction, and electrostatic interaction. Meanwhile, the EEC of modified biochar increased by 70 % than that of pristine biochar, thus improving nitrogen removal efficiency by 55.6 % and 9.5 % than CQ and BC group, respectively. Besides, the microorganism regulated by modified biochar produced more α-helix configuration, improving EPS barrier ability to CQ and sludge granulation. Lastly, metagenomic analysis revealed that modified biochar can stimulate the Wood-Ljungdahl pathway, increased the relative abundance of CODH from 0.74 % in CQ to 1.00 % in modified BC group. It favored the proliferation of autotrophic microorganisms, especially increased the relative abundance of anammox bacteria by 86.8 % than CQ group. This work will shed the light on integrating high-EEC biochar into anammox to cope with the micropollutants stress.

Multidimensional Insights into Organics Stress on Anammox systems: From a "Molecule-Cell-Ecology" Perspective

Anaerobic ammonium oxidation (anammox) is efficient and cost-effective for treating high-strength ammonia wastewater, but the organics in wastewater will affect its stability. To address this challenge, it is crucial to gain a deep understanding of the inhibitory effects and mechanisms of organics stress on anammox bacteria. The review provided a comprehensive classification of organics and evaluated their specific effects on the anammox system according to their respective characteristics. Based on the micro to macro perspective, the "molecule-cell-ecology" inhibitory mechanism of organics on anammox bacteria was proposed. The molecular observation systematically summarized the binding process and action sites of organics with anammox bacteria. At the cellular observation, the mechanisms of organics effects on extracellular polymeric substances, membranes, and anammoxosome of anammox bacteria were also expounded. At the ecological observation, the dynamic changes in coexisting populations and their role in organics transformation were further discussed. Further revelations on response mechanisms and inhibition mitigation strategies were proposed to broaden the applicability of anammox systems for organic wastewater. This review offered a multidimensional understanding of the organics inhibitory mechanism of anammox bacteria and provided a theoretical foundation for anammox systems.

Identification of extracellular polymeric substances layer barrier in chloroquine phosphate-disturbed anammox consortia and mechanism dissection on cytotoxic behavior by computational chemistry

The over-dosing use of chloroquine phosphate (CQ) poses severe threats to human beings and ecosystem due to the high persistence and biotoxicity. The discharge of CQ into wastewater would affect the biomass activity and process stability during the biological processes, e.g., anammox. However, the response mechanism of anammox consortia to CQ remain unknown. In this study, the accurate role of extracellular polymeric substances barrier in attenuating the negative effects of CQ, and the mechanism on cytotoxic behavior were dissected by molecular spectroscopy and computational chemistry. Low concentrations (≤6.0 mg/L) of CQ hardly affected the nitrogen removal performance due to the adaptive evolution of EPS barrier and anammox bacteria. Compact protein of EPS barrier can bind more CQ (0.24 mg) by hydrogen bond and van der Waals force, among which O-H and amide II region respond CQ binding preferentially. Importantly, EPS contributes to the microbiota reshape with selectively enriching Candidatus_Kuenenia for self-protection. Furthermore, the macroscopical cytotoxic behavior was dissected at a molecular level by CQ fate/distribution and computational chemistry, suggesting that the toxicity was ascribed to attack of CQ on functional proteins of anammox bacteria with atom N17 (f-=0.1209) and C2 (f+=0.1034) as the most active electrophilic and nucleophilic sites. This work would shed the light on the fate and risk of non-antibiotics in anammox process.

Effect of free ammonia on partial denitrification: Long-term performance, mechanism, and feasibility of PD/Anammox-FBBR for mature landfill leachate treatment

As a stable and effective approach for NO2--N accumulation, partial denitrification (PD) could significantly cut down operation cost, and PD/Anammox (PD/A) is a promising nitrogen removal process in wastewater treatment. The biotoxicity of free ammonia (FA) to nitrifying bacteria and anammox bacteria has been demonstrated, while whether FA affects PD bacteria is an open question. Here, long-term operation of PD-fixed bed biofilm reactor (PD-FBBR) treating synthetic wastewater and mature landfill leachate was conducted to reveal the mechanism concerning the effect of FA on PD bacteria. Stable NO2--N accumulation was achieved with NO3--N to NO2--N transformation ratio (NTR) of 60-70% during 280-day operation with FA ranged from 0 to 20.71 ± 0.23 mg/L, while NTR decreased and maintained at ∼30% when FA reached 40.59 ± 0.19 mg/L. Specific NOx--N reduction rate improved at low FA concentration (< 12 mg/L), while high FA level (> 25 mg/L) had inhibitory effect on PD bacteria. Under FA stress, more extracellular polymeric substances (EPS) were secreted, and the glnA gene abundance, glutamine synthase concentration, and glutamine concentration in cell and EPS significantly increased, indicating the enhancement of glutamine biosynthesis in PD bacteria for ammonia assimilation played an important role in response to FA stress. Metagenomic sequencing showed that FA stimulated the upregulation of narK (NO3--N/NO2--N antiporter) gene abundance and enhanced uptake of NO3--N and extrusion of NO2--N. Comamonas, unclassified_f__Comamonadaceae and Thauera were highly enriched in biofilm, which played a key role in the stable NO2--N accumulation. Furthermore, a novel two stage PD/A-FBBR was applied to mature landfill leachate treatment, and satisfactory total inorganic nitrogen removal efficiency ranged from 81.38 ± 3.56% to 89.16 ± 1.57% was obtained at relatively low COD/NO3--N of 2.57-2.84. Overall, these findings demonstrated how PD bacteria respond to FA stress and confirmed the feasibility of PD/A process in high FA wastewater treatment.

Insights into the reaction of anammox to exogenous pyridine: Long-term performance and micro mechanisms

Some industrial wastewaters contain high amounts of toxic nitrogen-containing heterocyclic compounds, which may inhibit the efficiency of biological treatment. This work systematically investigated how exogenous pyridine affected the anaerobic ammonia oxidation (anammox) system and discussed the microscopic response mechanisms based on genes and enzymes. The anammox efficiency was not seriously inhibited by pyridine less than 50 mg/L. Bacteria secreted more extracellular polymeric substances to resist pyridine stress. After 6 days stress with 80 mg/L pyridine, the nitrogen removal rate of anammox system lost 47.7%. Long-term stress of pyridine reduced anammox bacteria by 7.26% and the expression of functional genes by 45%. Pyridine could actively bind to hydrazine synthase and ammonium transporter. This work fills a research gap in the ongoing threat of pyridines to anammox, and has guiding value for the application of anammox process in the treatment of ammonia-rich wastewater containing pyridine.

Key enzymes involved in anammox-based processes for wastewater treatment: An applied overview

The anaerobic ammonium oxidation (anammox) process has attracted significant attention as an economic, robustness, and sustainable method for the treatment of nitrogen (N)-rich wastewater. Anammox bacteria (AnAOB) coexist with other microorganisms, and particularly with ammonia-oxidizing bacteria (AOB) and/or heterotrophic bacteria (HB), in symbiosis in favor of the substrate requirement (ammonium and nitrite) of the AnAOB being supplied by these other organisms. The dynamics of these microbial communities have a significant effect on the N-removal performance, but the corresponding metabolic pathways are still not fully understood. These processes involve many common metabolites that may act as key factors to control the symbiotic interactions between these organisms, to maximize N-removal efficiency from wastewater. Therefore, this work overviews the current state of knowledge about the metabolism of these microorganisms including key enzymes and intermediate metabolites and summarizes already reported experiences based on the employment of certain metabolites for the improvement of N-removal using anammox-based processes. PRACTITIONER POINTS: Approaches knowledge about the biochemistry and metabolic pathways involved in anammox-based processes. Some molecular tools can be used to determine enzymatic activity, serving as an optimization in nitrogen removal processes. Enzymatic evaluation allied to the physical-chemical and biomolecular analysis of the nitrogen removal processes expands the application in different effluents.