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Luo J, Wu Y, Fu H, Fu M, Liu M, Guo H, Jin L, Wang S. Shift in microorganism and functional gene abundance during completely autotrophic nitrogen removal over nitrite (CANON) process. JOURNAL OF ENVIRONMENTAL MANAGEMENT 2024; 359:121009. [PMID: 38718600 DOI: 10.1016/j.jenvman.2024.121009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2024] [Revised: 04/20/2024] [Accepted: 04/22/2024] [Indexed: 05/22/2024]
Abstract
Nitrification-denitrification process has failed to meet wastewater treatment standards. The completely autotrophic nitrite removal (CANON) process has a huge advantage in the field of low carbon/nitrogen wastewater nitrogen removal. However, slow start-up and system instability limit its applications. In this study, the time of the start-up CANON process was reduced by using bio-rope as loading materials. The establishing of graded dissolved oxygen improved the stability of the CANON process and enhanced the stratification effect between functional microorganisms. Microbial community structure and the abundance of nitrogen removal functional genes are also analyzed. The results showed that the CANON process was initiated within 75 days in the complete absence of anaerobic ammonium oxidizing bacteria (AnAOB) inoculation. The ammonium and nitrogen removal efficiencies of CANON process reached to 94.45% and 80.76% respectively. The results also showed that the relative abundance of nitrogen removal bacterial in the biofilm gradually increases with the dissolved oxygen content in the solution decreases. In contrast, the relative abundance of ammonia oxidizing bacteria was positively correlated with the dissolved oxygen content in the solution. The relative abundance of g__Candidatus_Brocadia in biofilm was 15.56%, and while g__Nitrosomonas was just 0.6613%. Metagenomic analysis showed that g__Candidatus_Brocadia also contributes 66.37% to the partial-nitrification functional gene Hao (K10535). This study presented a new idea for the cooperation between partial-nitrification and anammox, which improved the nitrogen removal system stability.
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Affiliation(s)
- Jiajun Luo
- Fujian Engineering and Research Center of Rural Sewage Treatment and Water Safety, Xiamen University of Technology, Xiamen, 361024, China
| | - Yicheng Wu
- Fujian Engineering and Research Center of Rural Sewage Treatment and Water Safety, Xiamen University of Technology, Xiamen, 361024, China
| | - Haiyan Fu
- Fujian Engineering and Research Center of Rural Sewage Treatment and Water Safety, Xiamen University of Technology, Xiamen, 361024, China.
| | - Muxing Fu
- Xiamen Zhongrenhemei Biotechnology Co., Xiamen, 361024, China
| | - Mian Liu
- Fujian Engineering and Research Center of Rural Sewage Treatment and Water Safety, Xiamen University of Technology, Xiamen, 361024, China
| | - Huibin Guo
- Fujian Engineering and Research Center of Rural Sewage Treatment and Water Safety, Xiamen University of Technology, Xiamen, 361024, China
| | - Lei Jin
- Fujian Engineering and Research Center of Rural Sewage Treatment and Water Safety, Xiamen University of Technology, Xiamen, 361024, China
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Wu B, Ran T, Liu S, Li Q, Cui X, Zhou Y. Biofilm bioactivity affects nitrogen metabolism in a push-flow microalgae-bacteria biofilm reactor during aeration-free greywater treatment. WATER RESEARCH 2023; 244:120461. [PMID: 37639992 DOI: 10.1016/j.watres.2023.120461] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/11/2023] [Revised: 07/30/2023] [Accepted: 08/07/2023] [Indexed: 08/31/2023]
Abstract
Non-aeration microalgae-bacteria biofilm has attracted increasing interest for its application in low cost wastewater treatment. However, it is unclear the quantified biofilm characteristics dynamics and how biofilm bioactivity affects performance and nitrogen metabolisms during wastewater treatment. In this work, a push-flow microalgae-bacteria biofilm reactor (PF-MBBfR) was developed for aeration-free greywater treatment. Comparatively, organic loading at 1.27 ± 0.10 kg COD/(m3⋅d) gave the highest biofilm concentration, density, specific oxygen generation (SOGR) and consumption rates (SOCR), and pollutants removal rates. Contributed to low residual linear alkylbenzene sulfonates and bioactivity, reactor downstream showed low bacteria and protein concentrations and SOCR (12.8 mg O2/g TSS·h), but high microalgae, carbohydrate, biofilm density, SOGR (49.4 mg O2/g TSS·h) and pollutants removal rates. Dissolved organic nitrogen (DON) showed higher molecular weight, CHONS and fraction with 4 atoms of N in reactor upstream. Most of nitrogen was fixed to newly synthesized biomass during assimilation process by related functional enzymes, minor contributed to denitrification due to low N2 emission. High nitrogen assimilation by microalgae showed high SOGR, which favored efficient multiple pollutants removal and reduced DON emission. Our findings favor the practical application of PF-MBBfR based on biofilm bioactivity, enhancing efficiency and reducing DON emission for low- energy-input wastewater treatment.
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Affiliation(s)
- Beibei Wu
- College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China
| | - Ting Ran
- College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China
| | - Sibei Liu
- College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China
| | - Qian Li
- College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China
| | - Xiaocai Cui
- College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China
| | - Yun Zhou
- College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China.
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3
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Li X, Feng Y, Zhang K, Zhou J, Sun J, Rong K, Liu S. Composite carrier enhanced bacterial adhesion and nitrogen removal in partial nitrification/anammox process. THE SCIENCE OF THE TOTAL ENVIRONMENT 2023; 868:161659. [PMID: 36657689 DOI: 10.1016/j.scitotenv.2023.161659] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/27/2022] [Revised: 01/12/2023] [Accepted: 01/12/2023] [Indexed: 06/17/2023]
Abstract
The rapid start-up and stable operation of one-stage (Partial nitrification/anammox) PN/A process for low-ammonium wastewater are difficult to be achieved, and many carriers are designed to solve this problem. Here, a composite carrier was developed, in which sepiolite and non-woven fabrics were assembled in polypropylene spherical shells. At the start-up phase, PA reactor using the composite carriers reached a higher nitrogen removal rate of 134.50 ± 19.60 mg·N·L-1d-1, in contrast to that of 48.85 ± 19.64 mg·N·L-1d-1 in the PB reactor without sepiolite carriers. When the final influent ammonium concentration of PN/A process is 100 mg/L, the total nitrogen removal efficiency can reach 72 ± 0.03 %. High biomass immobilization ability of composite carrier was evidenced by the greater adsorption trend between sludge and sepiolite than that between sludge and non-woven fabrics, where hydrophobic interaction and Van der Waals interaction played a major role. Extracellular protein (PN) content and the ratio of PN and extracellular polysaccharide of samples in PA were significantly higher than those in PB, verifying higher biofilm formation ability on the composite carrier. The composite carrier also increased the abundance of dominant bacteria in PN/A process, especially AOB, the relative abundance of which reached 46.11 %. And it increased the abundance of essential functional genes for nitrogen conversion as their perfect acid neutralizing effects. This study is of great significance in improving the start-up speed and stable operation of this process.
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Affiliation(s)
- Xinjue Li
- College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China; Key Laboratory of Water and Sediment Sciences, Ministry of Education of China, Beijing 100871, China
| | - Yiming Feng
- College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China; Key Laboratory of Water and Sediment Sciences, Ministry of Education of China, Beijing 100871, China
| | - Kuo Zhang
- College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China; Key Laboratory of Water and Sediment Sciences, Ministry of Education of China, Beijing 100871, China
| | - Jianhang Zhou
- College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China; Key Laboratory of Water and Sediment Sciences, Ministry of Education of China, Beijing 100871, China
| | - Jingqi Sun
- College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China; Key Laboratory of Water and Sediment Sciences, Ministry of Education of China, Beijing 100871, China
| | - Kaiyu Rong
- College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China; Key Laboratory of Water and Sediment Sciences, Ministry of Education of China, Beijing 100871, China
| | - Sitong Liu
- College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China; State Environmental Protection Key Laboratory of All Material Fluxes in River Ecosystems, Beijing 100871, China.
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4
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Effects of reducing, stabilizing, and antibiotic agents on "Candidatus Kuenenia stuttgartiensis". Appl Microbiol Biotechnol 2023; 107:1829-1843. [PMID: 36752812 PMCID: PMC10006275 DOI: 10.1007/s00253-023-12375-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2022] [Revised: 01/05/2023] [Accepted: 01/09/2023] [Indexed: 02/09/2023]
Abstract
Anaerobic ammon ium oxidizing (anammox) bacteria oxidize ammonium and reduce nitrite, producing N2, and could play a major role in energy-optimized wastewater treatment. However, sensitivity to various environmental conditions and slow growth currently hinder their wide application. Here, we attempted to determine online the effect of environmental stresses on anammox bacteria by using an overnight batch activity test with whole cells, in which anammox activity was calculated by quantifying N2 production via headspace-pressure monitoring. A planktonic mixed culture dominated by "Candidatus Kuenenia stuttgartiensis" strain CSTR1 was cultivated in a 30-L semi-continuous stirring tank reactor. In overnight resting-cell anammox activity tests, oxygen caused strong inhibition of anammox activity, which was reversed by sodium sulfite (30 µM). The tested antibiotics sulfamethoxazole, kanamycin, and ciprofloxacin elicited their effect on a dose-dependent manner; however, strain CSTR1 was highly resistant to sulfamethoxazole. Anammox activity was improved by activated carbon and Fe2O3. Protein expression analysis from resting cells after anammox activity stimulation revealed that NapC/NirT family cytochrome c (KsCSTR_12840), hydrazine synthase, hydrazine dehydrogenase, hydroxylamine oxidase, and nitrate:nitrite oxidoreductase were upregulated, while a putative hydroxylamine oxidoreductase HAO (KsCSTR_49490) was downregulated. These findings contribute to the growing knowledge on anammox bacteria physiology, eventually leading to the control of anammox bacteria growth and activity in real-world application. KEY POINTS: • Sulfite additions can reverse oxygen inhibition of the anammox process • Anammox activity was improved by activated carbon and ferric oxide • Sulfamethoxazole marginally affected anammox activity.
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5
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Pang S, Zhou Y, Yang L, Zhou J, Li X, Xia S. Simultaneous removal of nitrate and ammonium by hydrogen-based partial denitrification coupled with anammox in a membrane biofilm reactor. BIORESOURCE TECHNOLOGY 2023; 369:128443. [PMID: 36470489 DOI: 10.1016/j.biortech.2022.128443] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/20/2022] [Revised: 11/29/2022] [Accepted: 12/01/2022] [Indexed: 06/17/2023]
Abstract
Hydrogen-based membrane biofilm reactors (MBfRs) are effective for nitrogen removal. However, the safety of hydrogen limited the application of MBfR. Here, a hydrogen-based partial denitrification system coupled with anammox (H2-PDA) was constructed in an MBfR for reducing hydrogen demand significantly. The metabolomics and structures of microbial communities were analyzed to determine the phenotypic differences and drivers underlying denitrification, anammox, and H2-PDA. These findings indicated that total nitrogen (TN) removal increased from 57.1% in S1 to 93.7% in S2. During the H2-PDA process, partial denitrification and anammox contributed to TN removal by 93.7% and 6.3%, respectively. Community analysis indicated that the H2-PDA system was dominated by the genus Meiothermus, which is involved in partial denitrification. Collectively, these findings confirmed the feasibility of incorporating the H2-PDA process in a MBfR and form a foundation for the establishment of novel and practical methods for efficient nitrogen removal.
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Affiliation(s)
- Si Pang
- State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, China
| | - Yun Zhou
- College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China
| | - Lin Yang
- State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, China
| | - Jingzhou Zhou
- State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, China
| | - Xiaodi Li
- State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, China
| | - Siqing Xia
- State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, China.
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He HY, Niikura H, Du YL, Ryan KS. Synthetic and biosynthetic routes to nitrogen-nitrogen bonds. Chem Soc Rev 2022; 51:2991-3046. [PMID: 35311838 DOI: 10.1039/c7cs00458c] [Citation(s) in RCA: 27] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The nitrogen-nitrogen bond is a core feature of diverse functional groups like hydrazines, nitrosamines, diazos, and pyrazoles. Such functional groups are found in >300 known natural products. Such N-N bond-containing functional groups are also found in significant percentage of clinical drugs. Therefore, there is wide interest in synthetic and enzymatic methods to form nitrogen-nitrogen bonds. In this review, we summarize synthetic and biosynthetic approaches to diverse nitrogen-nitrogen-bond-containing functional groups, with a focus on biosynthetic pathways and enzymes.
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Affiliation(s)
- Hai-Yan He
- Department of Chemistry, University of British Columbia, Vancouver, Canada. .,Institute of Medicinal Biotechnology, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China.
| | - Haruka Niikura
- Department of Chemistry, University of British Columbia, Vancouver, Canada.
| | - Yi-Ling Du
- Institute of Pharmaceutical Biotechnology, Zhejiang University School of Medicine, Hangzhou, China
| | - Katherine S Ryan
- Department of Chemistry, University of British Columbia, Vancouver, Canada.
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Peng MW, Qi J, Yan P, Guan Y, Liu YY, Sun ZH, Zhang LJ, Weng X, Shen Y, Fang F, Guo JS, Chen YP. Insight into the structure and metabolic function of iron-rich nanoparticles in anammox bacteria. THE SCIENCE OF THE TOTAL ENVIRONMENT 2022; 806:150879. [PMID: 34627893 DOI: 10.1016/j.scitotenv.2021.150879] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/22/2021] [Revised: 10/03/2021] [Accepted: 10/04/2021] [Indexed: 06/13/2023]
Abstract
Anaerobic ammonium-oxidizing (anammox) bacteria are iron abundant and depend heavily on iron-binding proteins. The iron demand of anammox bacteria is relatively large. However, it still remains some doubts where these large quantities of available iron come from and how they are regulated in anammox bacteria. Herein, iron-rich nanoparticles in anammoxosomes were detected by synchrotron soft X-ray tomography coupled with scanning transmission X-ray microscopy (STXM). The iron-rich nanoparticles were identified as ferric oxide (α-Fe2O3) mineral cores, and the local atomic structure of iron-rich nanoparticles was obtained by X-ray absorption fine-structure (XAFS) spectra. The bacterioferritin of Q1Q315 and Q1Q5F8 were detected by proteomics analysis. On this basis, the metabolic pathway centered on iron-rich nanoparticles was proposed.
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Affiliation(s)
- Meng-Wen Peng
- Key Laboratory of the Three Gorges Reservoir Region's Eco-Environments of MOE, Chongqing University, Chongqing 400045, China; China Three Gorges Corporation, Beijing 100038, China
| | - Jing Qi
- Key Laboratory of the Three Gorges Reservoir Region's Eco-Environments of MOE, Chongqing University, Chongqing 400045, China
| | - Peng Yan
- Key Laboratory of the Three Gorges Reservoir Region's Eco-Environments of MOE, Chongqing University, Chongqing 400045, China
| | - Yong Guan
- National Synchrotron Radiation Laboratory, University of Science & Technology of China, Hefei 230026, China
| | - Ying-Ying Liu
- Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
| | - Zhi-Hu Sun
- National Synchrotron Radiation Laboratory, University of Science & Technology of China, Hefei 230026, China
| | - Li-Juan Zhang
- Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China
| | - Xun Weng
- Key Laboratory of the Three Gorges Reservoir Region's Eco-Environments of MOE, Chongqing University, Chongqing 400045, China
| | - Yu Shen
- National Base of International Science and Technology Cooperation for Intelligent Manufacturing Service, Chongqing Technology and Business University, Chongqing 400067, China
| | - Fang Fang
- Key Laboratory of the Three Gorges Reservoir Region's Eco-Environments of MOE, Chongqing University, Chongqing 400045, China
| | - Jin-Song Guo
- Key Laboratory of the Three Gorges Reservoir Region's Eco-Environments of MOE, Chongqing University, Chongqing 400045, China
| | - You-Peng Chen
- Key Laboratory of the Three Gorges Reservoir Region's Eco-Environments of MOE, Chongqing University, Chongqing 400045, China.
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8
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Akram M, Bock J, Dietl A, Barends TR. Specificity of Small c-Type Cytochromes in Anaerobic Ammonium Oxidation. ACS OMEGA 2021; 6:21457-21464. [PMID: 34471748 PMCID: PMC8388095 DOI: 10.1021/acsomega.1c02275] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/30/2021] [Accepted: 08/02/2021] [Indexed: 06/13/2023]
Abstract
Anaerobic ammonium oxidation (anammox) is a bacterial process in which ammonium and nitrite are combined into dinitrogen gas and water, yielding energy for the cell. This process relies on a series of redox reactions catalyzed by a set of enzymes, with electrons being shuttled to and from these enzymes, likely by small cytochrome c proteins. For this system to work productively, these electron carriers require a degree of specificity toward the various possible redox partners they encounter in the cell. Here, we compare two cytochrome c proteins from the anammox model organism Kuenenia stuttgartiensis. We show that they are highly homologous, are expressed at comparable levels, share the same fold, and display highly similar redox potentials, yet one of them accepts electrons from the metabolic enzyme hydroxylamine oxidase (HAO) efficiently, whereas the other does not. An analysis of the crystal structures supplemented by Monte Carlo simulations of the transient redox interactions suggests that this difference is at least partly due to the electrostatic field surrounding the proteins, illustrating one way in which the electron carriers in anammox could attain the required specificity. Moreover, the simulations suggest a different "outlet" for electrons on HAO than has traditionally been assumed.
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Akram M, Dietl A, Müller M, Barends TRM. Purification of the key enzyme complexes of the anammox pathway from DEMON sludge. Biopolymers 2021; 112:e23428. [PMID: 33798263 DOI: 10.1002/bip.23428] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2021] [Revised: 03/22/2021] [Accepted: 03/23/2021] [Indexed: 12/17/2022]
Abstract
Anaerobic Ammonium Oxidation ("anammox") is a bacterial process in which nitrite and ammonium are converted into nitrogen gas and water, yielding energy for the cell. Anammox is an important branch of the global biological nitrogen cycle, being responsible for up to 50% of the yearly nitrogen removal from the oceans. Strikingly, the anammox process uniquely relies on the extremely reactive and toxic compound hydrazine as a free intermediate. Given its global importance and biochemical novelty, there is considerable interest in the enzymes at the heart of the anammox pathway. Unfortunately, obtaining these enzymes in sufficiently large amounts for biochemical and structural studies is problematic, given the slow growth of pure cultures of anammox bacteria when high cell densities are required. However, the anammox process is being applied in wastewater treatment to remove nitrogenous waste in processes like DEamMONification (DEMON). In plants using such processes, which rely on a combination of aerobic ammonia-oxidizers and anammox organisms, kilogram amounts of anammox bacteria-containing sludge are readily available. Here, we report a protein isolation protocol starting from anammox cells present in DEMON sludge from a wastewater treatment plan that readily yields pure preparations of key anammox proteins in the tens of milligrams, including hydrazine synthase HZS and hydrazine dehydrogenase (HDH), as well as hydroxylamine oxidoreductase (HAO). HDH and HAO were active and of sufficient quality for biochemical studies and for HAO, the crystal structure could be determined. The method presented here provides a viable way to obtain materials for the study of proteins not only from the central anammox metabolism but also for the study of other exciting aspects of anammox bacteria, such as for example, their unusual ladderane lipids.
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Affiliation(s)
- Mohd Akram
- Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Heidelberg, Germany
| | - Andreas Dietl
- Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Heidelberg, Germany
| | - Melanie Müller
- Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Heidelberg, Germany
| | - Thomas R M Barends
- Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Heidelberg, Germany
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Structural and functional characterization of the intracellular filament-forming nitrite oxidoreductase multiprotein complex. Nat Microbiol 2021; 6:1129-1139. [PMID: 34267357 PMCID: PMC8387239 DOI: 10.1038/s41564-021-00934-8] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2021] [Accepted: 06/10/2021] [Indexed: 02/07/2023]
Abstract
Nitrate is an abundant nutrient and electron acceptor throughout Earth's biosphere. Virtually all nitrate in nature is produced by the oxidation of nitrite by the nitrite oxidoreductase (NXR) multiprotein complex. NXR is a crucial enzyme in the global biological nitrogen cycle, and is found in nitrite-oxidizing bacteria (including comammox organisms), which generate the bulk of the nitrate in the environment, and in anaerobic ammonium-oxidizing (anammox) bacteria which produce half of the dinitrogen gas in our atmosphere. However, despite its central role in biology and decades of intense study, no structural information on NXR is available. Here, we present a structural and biochemical analysis of the NXR from the anammox bacterium Kuenenia stuttgartiensis, integrating X-ray crystallography, cryo-electron tomography, helical reconstruction cryo-electron microscopy, interaction and reconstitution studies and enzyme kinetics. We find that NXR catalyses both nitrite oxidation and nitrate reduction, and show that in the cell, NXR is arranged in tubules several hundred nanometres long. We reveal the tubule architecture and show that tubule formation is induced by a previously unidentified, haem-containing subunit, NXR-T. The results also reveal unexpected features in the active site of the enzyme, an unusual cofactor coordination in the protein's electron transport chain, and elucidate the electron transfer pathways within the complex.
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Smeulders MJ, Peeters SH, van Alen T, de Bruijckere D, Nuijten GHL, op den Camp HJM, Jetten MSM, van Niftrik L. Nutrient Limitation Causes Differential Expression of Transport- and Metabolism Genes in the Compartmentalized Anammox Bacterium Kuenenia stuttgartiensis. Front Microbiol 2020; 11:1959. [PMID: 32903544 PMCID: PMC7438415 DOI: 10.3389/fmicb.2020.01959] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2020] [Accepted: 07/24/2020] [Indexed: 12/11/2022] Open
Abstract
Anaerobic ammonium-oxidizing (anammox) bacteria, members of the "Candidatus Brocadiaceae" family, play an important role in the nitrogen cycle and are estimated to be responsible for about half of the oceanic nitrogen loss to the atmosphere. Anammox bacteria combine ammonium with nitrite and produce dinitrogen gas via the intermediates nitric oxide and hydrazine (anammox reaction) while nitrate is formed as a by-product. These reactions take place in a specialized, membrane-enclosed compartment called the anammoxosome. Therefore, the substrates ammonium, nitrite and product nitrate have to cross the outer-, cytoplasmic-, and anammoxosome membranes to enter or exit the anammoxosome. The genomes of all anammox species harbor multiple copies of ammonium-, nitrite-, and nitrate transporter genes. Here we investigated how the distinct genes for ammonium-, nitrite-, and nitrate- transport were expressed during substrate limitation in membrane bioreactors. Transcriptome analysis of Kuenenia stuttgartiensis planktonic cells showed that four of the seven ammonium transporter homologs and two of the nine nitrite transporter homologs were significantly upregulated during ammonium-limited growth, while another ammonium transporter- and four nitrite transporter homologs were upregulated in nitrite limited growth conditions. The two nitrate transporters were expressed to similar levels in both conditions. In addition, genes encoding enzymes involved in the anammox reaction were differentially expressed, with those using nitrite as a substrate being upregulated under nitrite limited growth and those using ammonium as a substrate being upregulated during ammonium limitation. Taken together, these results give a first insight in the potential role of the multiple nutrient transporters in regulating transport of substrates and products in and out of the compartmentalized anammox cell.
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Affiliation(s)
| | | | | | | | | | | | | | - Laura van Niftrik
- Department of Microbiology, Institute for Water and Wetland Research, Faculty of Science, Radboud University Nijmegen, Nijmegen, Netherlands
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