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Hu S, Zheng L, Zhang H, Yang Y, Chen G, Meng H, Cheng K, Guo C, Wang Y, Li X, Liu T. Sequestration of Labile Organic Matter by Secondary Fe Minerals from Chemodenitrification: Insight into Mineral Protection Mechanisms. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2024; 58:11003-11015. [PMID: 38807562 DOI: 10.1021/acs.est.3c10134] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2024]
Abstract
Labile organic matter (OM) immobilized by secondary iron (Fe) minerals from chemodenitrification may be an effective way to immobilize organic carbon (OC). However, the underlying mechanisms of coupled chemodenitrification and OC sequestration are poorly understood. Here, OM immobilization by secondary Fe minerals from chemodenitrification was investigated at different C/Fe ratios. Kinetics of Fe(II) oxidation and nitrite reduction rates decreased with increasing C/Fe ratios. Despite efficient sequestration, the immobilization efficiency of OM by secondary minerals varied with the C/Fe ratios. Higher C/Fe ratios were conducive to the formation of ferrihydrite and lepidocrocite, with defects and nanopores. Three contributions, including inner-core Fe-O and edge- and corner-shared Fe-Fe interactions, constituted the local coordination environment of mineral-organic composites. Microscopic analysis at the molecular scale uncovered that labile OM was more likely to combine with secondary minerals with poor crystallinity to enhance its stability, and OM distributed within nanopores and defects had a higher oxidation state. After chemodenitrification, high molecular weight substances and substances high in unsaturation or O/C ratios including phenols, polycyclic aromatics, and carboxylic compounds exhibited a stronger affinity to Fe minerals in the treatments with lower C/Fe ratios. Collectively, labile OM immobilization can occur during chemodenitrification. The findings on OM sequestration coupled with chemodenitrification have significant implications for understanding the long-term cycling of Fe, C, and N, providing a potential strategy for OM immobilization in anoxic soils and sediments.
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Affiliation(s)
- Shiwen Hu
- National-Regional Joint Engineering Research Center for Soil Pollution Control and Remediation in South China, Guangdong Key Laboratory of Integrated Agro-environmental Pollution Control and Management, Institute of Eco-environmental and Soil Sciences, Guangdong Academy of Sciences, Guangzhou 510650, People's Republic of China
| | - Lirong Zheng
- Beijing Synchrotron Radiation Facility (BSRF), Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, People's Republic of China
| | - Hanyue Zhang
- CAS Key Laboratory of Mountain Ecological Restoration and Bioresource Utilization & Ecological Restoration and Biodiversity Conservation Key Laboratory of Sichuan Province, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, People's Republic of China
| | - Yang Yang
- National-Regional Joint Engineering Research Center for Soil Pollution Control and Remediation in South China, Guangdong Key Laboratory of Integrated Agro-environmental Pollution Control and Management, Institute of Eco-environmental and Soil Sciences, Guangdong Academy of Sciences, Guangzhou 510650, People's Republic of China
| | - Guojun Chen
- National-Regional Joint Engineering Research Center for Soil Pollution Control and Remediation in South China, Guangdong Key Laboratory of Integrated Agro-environmental Pollution Control and Management, Institute of Eco-environmental and Soil Sciences, Guangdong Academy of Sciences, Guangzhou 510650, People's Republic of China
| | - Hanbing Meng
- National-Regional Joint Engineering Research Center for Soil Pollution Control and Remediation in South China, Guangdong Key Laboratory of Integrated Agro-environmental Pollution Control and Management, Institute of Eco-environmental and Soil Sciences, Guangdong Academy of Sciences, Guangzhou 510650, People's Republic of China
| | - Kuan Cheng
- National-Regional Joint Engineering Research Center for Soil Pollution Control and Remediation in South China, Guangdong Key Laboratory of Integrated Agro-environmental Pollution Control and Management, Institute of Eco-environmental and Soil Sciences, Guangdong Academy of Sciences, Guangzhou 510650, People's Republic of China
| | - Chao Guo
- National-Regional Joint Engineering Research Center for Soil Pollution Control and Remediation in South China, Guangdong Key Laboratory of Integrated Agro-environmental Pollution Control and Management, Institute of Eco-environmental and Soil Sciences, Guangdong Academy of Sciences, Guangzhou 510650, People's Republic of China
| | - Ying Wang
- National-Regional Joint Engineering Research Center for Soil Pollution Control and Remediation in South China, Guangdong Key Laboratory of Integrated Agro-environmental Pollution Control and Management, Institute of Eco-environmental and Soil Sciences, Guangdong Academy of Sciences, Guangzhou 510650, People's Republic of China
| | - Xiaomin Li
- School of Environment, South China Normal University, Guangzhou 510006, China
| | - Tongxu Liu
- National-Regional Joint Engineering Research Center for Soil Pollution Control and Remediation in South China, Guangdong Key Laboratory of Integrated Agro-environmental Pollution Control and Management, Institute of Eco-environmental and Soil Sciences, Guangdong Academy of Sciences, Guangzhou 510650, People's Republic of China
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Zhou J, Deng W, Wu J, Xiang H, Shen X, Lin JG, Hong Y. Respiration and growth of Paracoccus denitrificans R-1 with nitrous oxide as an electron acceptor. Microbiol Spectr 2024; 12:e0381123. [PMID: 38647341 DOI: 10.1128/spectrum.03811-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2023] [Accepted: 03/22/2024] [Indexed: 04/25/2024] Open
Abstract
In the nitrogen biogeochemical cycle, the reduction of nitrous oxide (N2O) to N2 by N2O reductase, which is encoded by nosZ gene, is the only biological pathway for N2O consumption. In this study, we successfully isolated a strain of denitrifying Paracoccus denitrificans R-1 from sewage treatment plant sludge. This strain has strong N2O reduction capability, and the average N2O reduction rate was 5.10 ± 0.11 × 10-9 µmol·h-1·cell-1 under anaerobic condition in a defined medium. This reduction was accompanied by the stoichiometric consumption of acetate over time when N2O served as the sole electron acceptor and the reduction can yield energy to support microbial growth, suggesting that microbial N2O reduction is related to the energy generation process. Genomic analysis showed that the gene cluster encoding N2O reductase of P. denitrificans R-1 was composed of nosR, nosZ, nosD, nosF, nosY, nosL, and nosZ, which was identified as that in other strains in clade I. Respiratory inhibitors test indicated that the pathway of electron transport for N2O reduction was different from that of the traditional electron transport chain for aerobic respiration. Cu2+, silver nanoparticles, O2, and acidic conditions can strongly inhibit the reduction, whereas NO3- or NH4+ can promote it. These findings suggest that modular N2O reduction of P. denitrificans R-1 is linked to the electron transport and energy conservation, and dissimilatory N2O reduction is a form of microbial anaerobic respiration. IMPORTANCE Nitrous oxide (N2O) is a potent greenhouse gas and contributor to ozone layer destruction, and atmospheric N2O has increased steadily over the past century due to human activities. The release of N2O from fixed N is almost entirely controlled by microbial N2O reductase activities. Here, we investigated the ability to obtain energy for the growth of Paracoccus denitrificans R-1 by coupling the oxidation of various electron donors to N2O reduction. The modular N2O reduction process of denitrifying microorganism not only can consume N2O produced by itself but also can consume the external N2O generated from biological or abiotic pathways under suitable condition, which should be critical for controlling the release of N2O from ecosystems into the atmosphere.
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Affiliation(s)
- Jiaxian Zhou
- Institute of Environmental Research at Greater Bay Area; Key Laboratory for Water Quality and Conservation of the Pearl River Delta, Ministry of Education, Guangzhou University, Guangzhou, China
- School of Environmental Science and Engineering, Guangzhou University, Guangzhou, China
| | - Wenfang Deng
- Institute of Environmental Research at Greater Bay Area; Key Laboratory for Water Quality and Conservation of the Pearl River Delta, Ministry of Education, Guangzhou University, Guangzhou, China
| | - Jiapeng Wu
- Institute of Environmental Research at Greater Bay Area; Key Laboratory for Water Quality and Conservation of the Pearl River Delta, Ministry of Education, Guangzhou University, Guangzhou, China
| | - Hua Xiang
- Institute of Environmental Research at Greater Bay Area; Key Laboratory for Water Quality and Conservation of the Pearl River Delta, Ministry of Education, Guangzhou University, Guangzhou, China
| | - Xiaomei Shen
- Institute of Environmental Research at Greater Bay Area; Key Laboratory for Water Quality and Conservation of the Pearl River Delta, Ministry of Education, Guangzhou University, Guangzhou, China
| | - Jih-Gaw Lin
- Institute of Environmental Engineering, National Yangming Chiao Tung University, Hsinchu City, Taiwan
| | - Yiguo Hong
- Institute of Environmental Research at Greater Bay Area; Key Laboratory for Water Quality and Conservation of the Pearl River Delta, Ministry of Education, Guangzhou University, Guangzhou, China
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Awala SI, Gwak JH, Kim Y, Jung MY, Dunfield PF, Wagner M, Rhee SK. Nitrous oxide respiration in acidophilic methanotrophs. Nat Commun 2024; 15:4226. [PMID: 38762502 PMCID: PMC11102522 DOI: 10.1038/s41467-024-48161-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2024] [Accepted: 04/22/2024] [Indexed: 05/20/2024] Open
Abstract
Aerobic methanotrophic bacteria are considered strict aerobes but are often highly abundant in hypoxic and even anoxic environments. Despite possessing denitrification genes, it remains to be verified whether denitrification contributes to their growth. Here, we show that acidophilic methanotrophs can respire nitrous oxide (N2O) and grow anaerobically on diverse non-methane substrates, including methanol, C-C substrates, and hydrogen. We study two strains that possess N2O reductase genes: Methylocella tundrae T4 and Methylacidiphilum caldifontis IT6. We show that N2O respiration supports growth of Methylacidiphilum caldifontis at an extremely acidic pH of 2.0, exceeding the known physiological pH limits for microbial N2O consumption. Methylocella tundrae simultaneously consumes N2O and CH4 in suboxic conditions, indicating robustness of its N2O reductase activity in the presence of O2. Furthermore, in O2-limiting conditions, the amount of CH4 oxidized per O2 reduced increases when N2O is added, indicating that Methylocella tundrae can direct more O2 towards methane monooxygenase. Thus, our results demonstrate that some methanotrophs can respire N2O independently or simultaneously with O2, which may facilitate their growth and survival in dynamic environments. Such metabolic capability enables these bacteria to simultaneously reduce the release of the key greenhouse gases CO2, CH4, and N2O.
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Affiliation(s)
- Samuel Imisi Awala
- Department of Biological Sciences and Biotechnology, Chungbuk National University, 1 Chungdae-ro, Seowon-Gu, Cheongju, 28644, Republic of Korea
- Center for Ecology and Environmental Toxicology, Chungbuk National University, 1 Chungdae-Ro, Seowon-Gu, Cheongju, 28644, South Korea
| | - Joo-Han Gwak
- Department of Biological Sciences and Biotechnology, Chungbuk National University, 1 Chungdae-ro, Seowon-Gu, Cheongju, 28644, Republic of Korea
| | - Yongman Kim
- Department of Biological Sciences and Biotechnology, Chungbuk National University, 1 Chungdae-ro, Seowon-Gu, Cheongju, 28644, Republic of Korea
| | - Man-Young Jung
- Interdisciplinary Graduate Programme in Advance Convergence Technology and Science, Jeju National University, Jeju, Republic of Korea
- Department of Science Education, Jeju National University, Jeju, Republic of Korea
- Jeju Microbiome Center, Jeju National University, Jeju, Republic of Korea
| | - Peter F Dunfield
- Department of Biological Sciences, University of Calgary, 2500 University Dr. NW, Calgary, AB, T2N 1N4, Canada
| | - Michael Wagner
- Division of Microbial Ecology, Department of Microbiology and Ecosystem Science, Centre for Microbiology and Environmental Systems Science, University of Vienna, Althanstrasse 14, A-1090, Vienna, Austria
- Department of Chemistry and Bioscience, Center for Microbial Communities, Aalborg University, Fredrik Bajers Vej 7H, 9220, Aalborg, Denmark
| | - Sung-Keun Rhee
- Department of Biological Sciences and Biotechnology, Chungbuk National University, 1 Chungdae-ro, Seowon-Gu, Cheongju, 28644, Republic of Korea.
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Bromfield ESP, Cloutier S. Bradyrhizobium ontarionense sp. nov., a novel bacterial symbiont isolated from Aeschynomene indica (Indian jointvetch), harbours photosynthesis, nitrogen fixation and nitrous oxide (N 2O) reductase genes. Antonie Van Leeuwenhoek 2024; 117:69. [PMID: 38647727 PMCID: PMC11035471 DOI: 10.1007/s10482-024-01940-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2023] [Accepted: 02/02/2024] [Indexed: 04/25/2024]
Abstract
A novel bacterial symbiont, strain A19T, was previously isolated from a root-nodule of Aeschynomene indica and assigned to a new lineage in the photosynthetic clade of the genus Bradyrhizobium. Here data are presented for the detailed genomic and taxonomic analyses of novel strain A19T. Emphasis is placed on the analysis of genes of practical or ecological significance (photosynthesis, nitrous oxide reductase and nitrogen fixation genes). Phylogenomic analysis of whole genome sequences as well as 50 single-copy core gene sequences placed A19T in a highly supported lineage distinct from described Bradyrhizobium species with B. oligotrophicum as the closest relative. The digital DNA-DNA hybridization and average nucleotide identity values for A19T in pair-wise comparisons with close relatives were far lower than the respective threshold values of 70% and ~ 96% for definition of species boundaries. The complete genome of A19T consists of a single 8.44 Mbp chromosome and contains a photosynthesis gene cluster, nitrogen-fixation genes and genes encoding a complete denitrifying enzyme system including nitrous oxide reductase implicated in the reduction of N2O, a potent greenhouse gas, to inert dinitrogen. Nodulation and type III secretion system genes, needed for nodulation by most rhizobia, were not detected. Data for multiple phenotypic tests complemented the sequence-based analyses. Strain A19T elicits nitrogen-fixing nodules on stems and roots of A. indica plants but not on soybeans or Macroptilium atropurpureum. Based on the data presented, a new species named Bradyrhizobium ontarionense sp. nov. is proposed with strain A19T (= LMG 32638T = HAMBI 3761T) as the type strain.
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Affiliation(s)
- Eden S P Bromfield
- Agriculture and Agri-Food Canada, 960 Carling Ave., Ottawa, K1A 0C6, Canada.
| | - Sylvie Cloutier
- Agriculture and Agri-Food Canada, 960 Carling Ave., Ottawa, K1A 0C6, Canada
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LaSarre B, Morlen R, Neumann GC, Harwood CS, McKinlay JB. Nitrous oxide reduction by two partial denitrifying bacteria requires denitrification intermediates that cannot be respired. Appl Environ Microbiol 2024; 90:e0174123. [PMID: 38078768 PMCID: PMC10807417 DOI: 10.1128/aem.01741-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2023] [Accepted: 11/04/2023] [Indexed: 01/25/2024] Open
Abstract
Denitrification is a form of anaerobic respiration wherein nitrate (NO3-) is sequentially reduced via nitrite (NO2-), nitric oxide, and nitrous oxide (N2O) to dinitrogen gas (N2) by four reductase enzymes. Partial denitrifying bacteria possess only one or some of these four reductases and use them as independent respiratory modules. However, it is unclear if partial denitrifiers sense and respond to denitrification intermediates outside of their reductase repertoire. Here, we tested the denitrifying capabilities of two purple nonsulfur bacteria, Rhodopseudomonas palustris CGA0092 and Rhodobacter capsulatus SB1003. Each had denitrifying capabilities that matched their genome annotation; CGA0092 reduced NO2- to N2, and SB1003 reduced N2O to N2. For each bacterium, N2O reduction could be used both for electron balance during growth on electron-rich organic compounds in light and for energy transformation via respiration in darkness. However, N2O reduction required supplementation with a denitrification intermediate, including those for which there was no associated denitrification enzyme. For CGA0092, NO3- served as a stable, non-catalyzable molecule that was sufficient to activate N2O reduction. Using a β-galactosidase reporter, we found that NO3- acted, at least in part, by stimulating N2O reductase gene expression. In SB1003, NO2- but not NO3- activated N2O reduction, but NO2- was slowly removed, likely by a promiscuous enzyme activity. Our findings reveal that partial denitrifiers can still be subject to regulation by denitrification intermediates that they cannot use.IMPORTANCEDenitrification is a form of microbial respiration wherein nitrate is converted via several nitrogen oxide intermediates into harmless dinitrogen gas. Partial denitrifying bacteria, which individually have some but not all denitrifying enzymes, can achieve complete denitrification as a community by cross-feeding nitrogen oxide intermediates. However, the last intermediate, nitrous oxide (N2O), is a potent greenhouse gas that often escapes, motivating efforts to understand and improve the efficiency of denitrification. Here, we found that at least some partial denitrifying N2O reducers can sense and respond to nitrogen oxide intermediates that they cannot otherwise use. The regulatory effects of nitrogen oxides on partial denitrifiers are thus an important consideration in understanding and applying denitrifying bacterial communities to combat greenhouse gas emissions.
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Affiliation(s)
- Breah LaSarre
- Department of Biology, Indiana University, Bloomington, Indiana, USA
| | - Ryan Morlen
- Department of Microbiology, University of Washington, Seattle, Washington, USA
| | - Gina C. Neumann
- Department of Biology, Indiana University, Bloomington, Indiana, USA
| | - Caroline S. Harwood
- Department of Microbiology, University of Washington, Seattle, Washington, USA
| | - James B. McKinlay
- Department of Biology, Indiana University, Bloomington, Indiana, USA
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Tomás-Gallardo L, Cabrera JJ, Mesa S. Surface Plasmon Resonance as a Tool to Elucidate the Molecular Determinants of Key Transcriptional Regulators Controlling Rhizobial Lifestyles. Methods Mol Biol 2024; 2751:145-163. [PMID: 38265715 DOI: 10.1007/978-1-0716-3617-6_10] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2024]
Abstract
Bacteria must be provided with a battery of tools integrated into regulatory networks, in order to respond and, consequently, adapt their physiology to changing environments. Within these networks, transcription factors finely orchestrate the expression of genes in response to a variety of signals, by recognizing specific DNA sequences at their promoter regions. Rhizobia are host-interacting soil bacteria that face severe changes to adapt their physiology from free-living conditions to the nitrogen-fixing endosymbiotic state inside root nodules associated with leguminous plants. One of these cues is the low partial pressure of oxygen within root nodules.Surface plasmon resonance (SPR) constitutes a technique that allows to measure molecular interactions dynamics at real time by detecting changes in the refractive index of a surface. Here, we implemented the SPR methodology to analyze the discriminatory determinants of transcription factors for specific interaction with their target genes. We focused on FixK2, a CRP/FNR-type protein with a central role in the complex oxygen-responsive regulatory network in the soybean endosymbiont Bradyrhizobium diazoefficiens. Our study unveiled relevant residues for protein-DNA interaction as well as allowed us to monitor kinetics and stability protein-DNA complex. We believe that this approach can be employed for the characterization of other relevant transcription factors which can assist to the better understanding of the adaptation of bacteria with agronomic or human interest to their different modes of life.
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Affiliation(s)
- Laura Tomás-Gallardo
- Proteomics and Biochemistry Unit, Andalusian Centre for Developmental Biology, CSIC-Junta de Andalucía-Pablo de Olavide University, Seville, Spain.
| | - Juan J Cabrera
- Department of Soil and Plant Microbiology, Estación Experimental del Zaidín, CSIC, Granada, Spain
| | - Socorro Mesa
- Department of Soil and Plant Microbiology, Estación Experimental del Zaidín, CSIC, Granada, Spain
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Larralde-Piña IA, Acuña-Askar K, Villanueva-Rodríguez M, Guzmán-Mar JL, Murillo-Sierra JC, Ruiz-Ruiz EJ. An optimized electro-fenton pretreatment for the degradation and mineralization of a mixture of ofloxacin, norfloxacin, and ciprofloxacin. CHEMOSPHERE 2023; 344:140339. [PMID: 37820878 DOI: 10.1016/j.chemosphere.2023.140339] [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: 06/22/2023] [Revised: 09/18/2023] [Accepted: 09/28/2023] [Indexed: 10/13/2023]
Abstract
The electro-Fenton process (EFP) is a powerful advanced oxidation process beneficial to treating recalcitrant contaminants, and there has been a continuing interest in combining this technology to enhance the efficiency of conventional wastewater treatment processes. In this work, an optimized EFP process is performed as pretreatment for the degradation and mineralization of three blank fluoroquinolones (FQs) drugs: ofloxacin (OFL), norfloxacin (NOR), and ciprofloxacin (CIP). The optimization of the experiment was carried out using a Box-Behnken experimental design. Faster and complete degradation of the drugs mixture was achieved in 90 min with 61.12 ± 2.0% of mineralization in 180 min, under the optimized conditions: j = 244.0 mA cm-2, [Fe2+] = 0.31 mM, and [FQs] = 87.0 mg L-1. Furthermore, a low toxicity effluent was obtained in 90 min of the experiment, according to bioassay toxicity with Vibrio fischeri. Five short-chain carboxylic acids, including oxalic, maleic, oxamic, formic, and fumaric acids, were detected and quantified, in addition to F- and NO3- inorganic ions. The inhibition of the reactive oxygen species with scavenger proof was also evaluated in this paper.
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Affiliation(s)
- I A Larralde-Piña
- Universidad Autónoma de Nuevo León (UANL), Facultad de Ciencias Químicas, Cd. Universitaria, San Nicolás de Los Garza, Nuevo León, C.P. 66455, México
| | - K Acuña-Askar
- Universidad Autónoma de Nuevo León (UANL), Facultad de Medicina, Depto. de Microbiología, Monterrey, Nuevo León, C.P. 64460, México
| | - M Villanueva-Rodríguez
- Universidad Autónoma de Nuevo León (UANL), Facultad de Ciencias Químicas, Cd. Universitaria, San Nicolás de Los Garza, Nuevo León, C.P. 66455, México
| | - J L Guzmán-Mar
- Universidad Autónoma de Nuevo León (UANL), Facultad de Ciencias Químicas, Cd. Universitaria, San Nicolás de Los Garza, Nuevo León, C.P. 66455, México
| | - J C Murillo-Sierra
- Universidad de Concepción, Facultad de Ciencias Químicas, Edmundo Larenas 129, Concepción, Chile
| | - E J Ruiz-Ruiz
- Universidad Autónoma de Nuevo León (UANL), Facultad de Ciencias Químicas, Cd. Universitaria, San Nicolás de Los Garza, Nuevo León, C.P. 66455, México.
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Cisternas J, Rodríguez C, Serrano J, Leiva E. Study of the key biotic and abiotic parameters influencing ammonium removal from wastewaters by Fe 3+-mediated anaerobic ammonium oxidation (Feammox). CHEMOSPHERE 2023; 339:139463. [PMID: 37480952 DOI: 10.1016/j.chemosphere.2023.139463] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/13/2023] [Revised: 06/27/2023] [Accepted: 07/09/2023] [Indexed: 07/24/2023]
Abstract
The release of ammonia (as NH4+) into water bodies causes serious environmental problems. Therefore, the removal of ammonia from wastewater effluents has become a worldwide concern. New autotrophic biological alternatives for ammonia removal could reduce the limitations of conventional organic carbon-dependent nitrification-denitrification methods. Here, the potential of anaerobic ammonium oxidation coupled to Fe3+ reduction (a process known as Feammox) is studied in wastewater treatment plants of the yeast and beer production industry, not related to ammonium or iron treatment. This process is presented as a viable option to improve the efficiency of ammonia removal from wastewater. The results of this study show that enrichments under Feammox conditions achieved removals of 28.19-32.25% of the total NH4+. The highest rates of ammonium removal and Fe3+ reduction were achieved using FeCl3 as iron source and pH = 7.0. Different environmental conditions for the enrichments were studied and it was found that the use of sodium acetate as a carbon source and an incubation temperature of 35 °C presented higher rates of iron reduction and higher increase in nitrate concentration, related to ammonium oxidative processes. Likewise, the presence of relevant species of the iron and nitrogen cycles as Ferrovum myxofaciens, Geobacter spp, Shewanella spp, Albidiferax ferrireducens and Anammox was verified, supporting the findings of this study. These results provide information that may be relevant to the potential applicability of Feammox to treat wastewater with high ammonia load and could help develop cost-effective and environmentally friendly methods for ammonium removal in wastewater treatment plants.
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Affiliation(s)
- Jaime Cisternas
- Departamento de Química Inorgánica, Facultad de Química, Pontificia Universidad Católica de Chile, Avenida Vicuña Mackenna 4860, Macul, 7820436, Santiago, Chile; Escuela de Biotecnología, Universidad Mayor, Camino La Pirámide 5750, Huechuraba, Santiago 8580745, Chile.
| | - Carolina Rodríguez
- Departamento de Química Inorgánica, Facultad de Química, Pontificia Universidad Católica de Chile, Avenida Vicuña Mackenna 4860, Macul, 7820436, Santiago, Chile.
| | - Jennyfer Serrano
- Escuela de Biotecnología, Universidad Mayor, Camino La Pirámide 5750, Huechuraba, Santiago 8580745, Chile.
| | - Eduardo Leiva
- Departamento de Química Inorgánica, Facultad de Química, Pontificia Universidad Católica de Chile, Avenida Vicuña Mackenna 4860, Macul, 7820436, Santiago, Chile; Departamento de Ingeniería Hidráulica y Ambiental, Pontificia Universidad Católica de Chile, Avenida Vicuña Mackenna 4860, Macul, 7820436, Santiago, Chile.
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Sanow S, Kuang W, Schaaf G, Huesgen P, Schurr U, Roessner U, Watt M, Arsova B. Molecular Mechanisms of Pseudomonas-Assisted Plant Nitrogen Uptake: Opportunities for Modern Agriculture. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2023; 36:536-548. [PMID: 36989040 DOI: 10.1094/mpmi-10-22-0223-cr] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/19/2023]
Abstract
Pseudomonas spp. make up 1.6% of the bacteria in the soil and are found throughout the world. More than 140 species of this genus have been identified, some beneficial to the plant. Several species in the family Pseudomonadaceae, including Azotobacter vinelandii AvOP, Pseudomonas stutzeri A1501, Pseudomonas stutzeri DSM4166, Pseudomonas szotifigens 6HT33bT, and Pseudomonas sp. strain K1 can fix nitrogen from the air. The genes required for these reactions are organized in a nitrogen fixation island, obtained via horizontal gene transfer from Klebsiella pneumoniae, Pseudomonas stutzeri, and Azotobacter vinelandii. Today, this island is conserved in Pseudomonas spp. from different geographical locations, which, in turn, have evolved to deal with different geo-climatic conditions. Here, we summarize the molecular mechanisms behind Pseudomonas-driven plant growth promotion, with particular focus on improving plant performance at limiting nitrogen (N) and improving plant N content. We describe Pseudomonas-plant interaction strategies in the soil, noting that the mechanisms of denitrification, ammonification, and secondary metabolite signaling are only marginally explored. Plant growth promotion is dependent on the abiotic conditions and differs at sufficient and deficient N. The molecular controls behind different plant responses are not fully elucidated. We suggest that superposition of transcriptome, proteome, and metabolome data and their integration with plant phenotype development through time will help fill these gaps. The aim of this review is to summarize the knowledge behind Pseudomonas-driven nitrogen fixation and to point to possible agricultural solutions. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.
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Affiliation(s)
- Stefan Sanow
- Institute for Bio- and Geosciences, Plant Sciences (IBG-2), Forschungszentrum Juelich GmbH, Germany
- School of BioSciences, Faculty of Science, The University of Melbourne, Parkville, 3010 Victoria, Australia
| | - Weiqi Kuang
- College of life and Environmental Sciences, Hunan University of Arts and Science, China
| | - Gabriel Schaaf
- Institute of Crop Science and Resource Conservation, University of Bonn, 53115 Bonn, Germany
| | - Pitter Huesgen
- Central institute for Engineering, Electronics and Analytics (ZEA-3), Forschungszentrum Juelich GmbH, Germany
| | - Ulrich Schurr
- Institute for Bio- and Geosciences, Plant Sciences (IBG-2), Forschungszentrum Juelich GmbH, Germany
| | - Ute Roessner
- Research School of Biology, The Australian National University, Acton, 2601 Australian Capital Territory, Australia
| | - Michelle Watt
- School of BioSciences, Faculty of Science, The University of Melbourne, Parkville, 3010 Victoria, Australia
| | - Borjana Arsova
- Institute for Bio- and Geosciences, Plant Sciences (IBG-2), Forschungszentrum Juelich GmbH, Germany
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10
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Denitrification by Bradyrhizobia under Feast and Famine and the Role of the bc1 Complex in Securing Electrons for N 2O Reduction. Appl Environ Microbiol 2023; 89:e0174522. [PMID: 36662572 PMCID: PMC9972998 DOI: 10.1128/aem.01745-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Rhizobia living as microsymbionts inside nodules have stable access to carbon substrates, but also must survive as free-living bacteria in soil where they are starved for carbon and energy most of the time. Many rhizobia can denitrify, thus switch to anaerobic respiration under low O2 tension using N-oxides as electron acceptors. The cellular machinery regulating this transition is relatively well known from studies under optimal laboratory conditions, while little is known about this regulation in starved organisms. It is, for example, not known if the strong preference for N2O- over NO3- reduction in bradyrhizobia is retained under carbon limitation. Here, we show that starved cultures of a Bradyrhizobium strain with respiration rates 1 to 18% of well-fed cultures reduced all available N2O before touching provided NO3-. These organisms, which carry out complete denitrification, have the periplasmic nitrate reductase NapA but lack the membrane-bound nitrate reductase NarG. Proteomics showed similar levels of NapA and NosZ (N2O reductase), excluding that the lack of NO3- reduction was due to low NapA abundance. Instead, this points to a metabolic-level phenomenon where the bc1 complex, which channels electrons to NosZ via cytochromes, is a much stronger competitor for electrons from the quinol pool than the NapC enzyme, which provides electrons to NapA via NapB. The results contrast the general notion that NosZ activity diminishes under carbon limitation and suggest that bradyrhizobia carrying NosZ can act as strong sinks for N2O under natural conditions, implying that this criterion should be considered in the development of biofertilizers. IMPORTANCE Legume cropped farmlands account for substantial N2O emissions globally. Legumes are commonly inoculated with N2-fixing bacteria, rhizobia, to improve crop yields. Rhizobia belonging to Bradyrhizobium, the microsymbionts of several economically important legumes, are generally capable of denitrification but many lack genes encoding N2O reductase and will be N2O sources. Bradyrhizobia with complete denitrification will instead act as sinks since N2O-reduction efficiently competes for electrons over nitrate reduction in these organisms. This phenomenon has only been demonstrated under optimal conditions and it is not known how carbon substrate limitation, which is the common situation in most soils, affects the denitrification phenotype. Here, we demonstrate that bradyrhizobia retain their strong preference for N2O under carbon starvation. The findings add basic knowledge about mechanisms controlling denitrification and support the potential for developing novel methods for greenhouse gas mitigation based on legume inoculants with the dual capacity to optimize N2 fixation and minimize N2O emission.
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11
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Fang J, Yan L, Tan M, Li G, Liang Y, Li K. Nitrogen Removal Characteristics of a Marine Denitrifying Pseudomonas stutzeri BBW831 and a Simplified Strategy for Improving the Denitrification Performance Under Stressful Conditions. MARINE BIOTECHNOLOGY (NEW YORK, N.Y.) 2023; 25:109-122. [PMID: 36446961 DOI: 10.1007/s10126-022-10185-1] [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: 08/20/2022] [Accepted: 11/18/2022] [Indexed: 06/16/2023]
Abstract
A marine aerobic denitrifying bacterium was isolated and identified as Pseudomonas stutzeri BBW831 from the seabed silt of Beibu Gulf in China. According to the genome analysis, P. stutzeri BBW831 possessed a total of 14 genes (narG, narH, narI, narJ, napA, napB, nirB, nirD, nirS, norB, norC, norD, norQ, and nosZ) responsible for fully functional enzymes (nitrate reductase, nitrite reductase, nitric oxide reductase, and nitrous oxide reductase) involved in the complete aerobic denitrification pathway, suggesting that it had the potential for reducing nitrate to the final N2. Denitrification results showed that P. stutzeri BBW831 exhibited efficient nitrogen removal characteristics. Within 12 h, the NO3--N removal efficiency and rate reached 94.64% and 13.09 mg·L-1·h-1 under 166.10 ± 3.75 mg/L NO3--N as the sole nitrogen source, and removal efficiency of the mixed nitrogen (50.50 ± 0.55, 62.28 ± 0.74, and 64.26 ± 0.90 mg/L of initial NH4+-N, NO3--N, and NO2--N, respectively) was nearly 100%. Furthermore, a simplified strategy, by augmenting the inoculation biomass, was developed for promoting the nitrogen removal performance under high levels of NO2--N and salinity. As a result, the removal efficiency of the initial NO2--N up to approximately 130 mg/L reached 99.46% within 8 h, and the NO3--N removal efficiency achieved at 59.46% under the NaCl concentration even up to 50 g/L. The C/N ratio of 10 with organic acid salt such as trisodium citrate and sodium acetate as the carbon source was most conducive for cell growth and nitrogen removal by P. stutzeri BBW831, respectively. In conclusion, the marine P. stutzeri BBW831 contained the functional genes responsible for a complete aerobic denitrification pathway (NO3--N → NO2--N → NO → N2O → N2), and had great potential for the practical treatment of high-salinity nitrogenous mariculture wastewater.
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Affiliation(s)
- Jianhao Fang
- College of Food Science and Technology Guangdong Provincial Key Laboratory of Aquatic Product Processing and Safety Guangdong Province Engineering Laboratory for Marine Biological Products, Key Laboratory of Advanced Processing of Aquatic Product of Guangdong Higher Education Institution, Guangdong Ocean University, Guangdong Provincial Engineering Technology Research Center of Seafood, Zhanjiang, 524088, China
- Collaborative Innovation Center of Seafood Deep Processing, Dalian Polytechnic University, Dalian, 116034, China
| | - Luqi Yan
- College of Food Science and Technology Guangdong Provincial Key Laboratory of Aquatic Product Processing and Safety Guangdong Province Engineering Laboratory for Marine Biological Products, Key Laboratory of Advanced Processing of Aquatic Product of Guangdong Higher Education Institution, Guangdong Ocean University, Guangdong Provincial Engineering Technology Research Center of Seafood, Zhanjiang, 524088, China
- Collaborative Innovation Center of Seafood Deep Processing, Dalian Polytechnic University, Dalian, 116034, China
| | - Minghui Tan
- College of Food Science and Technology Guangdong Provincial Key Laboratory of Aquatic Product Processing and Safety Guangdong Province Engineering Laboratory for Marine Biological Products, Key Laboratory of Advanced Processing of Aquatic Product of Guangdong Higher Education Institution, Guangdong Ocean University, Guangdong Provincial Engineering Technology Research Center of Seafood, Zhanjiang, 524088, China.
- Collaborative Innovation Center of Seafood Deep Processing, Dalian Polytechnic University, Dalian, 116034, China.
| | - Ganghui Li
- College of Food Science and Technology Guangdong Provincial Key Laboratory of Aquatic Product Processing and Safety Guangdong Province Engineering Laboratory for Marine Biological Products, Key Laboratory of Advanced Processing of Aquatic Product of Guangdong Higher Education Institution, Guangdong Ocean University, Guangdong Provincial Engineering Technology Research Center of Seafood, Zhanjiang, 524088, China
- Collaborative Innovation Center of Seafood Deep Processing, Dalian Polytechnic University, Dalian, 116034, China
| | - Yingyin Liang
- College of Food Science and Technology Guangdong Provincial Key Laboratory of Aquatic Product Processing and Safety Guangdong Province Engineering Laboratory for Marine Biological Products, Key Laboratory of Advanced Processing of Aquatic Product of Guangdong Higher Education Institution, Guangdong Ocean University, Guangdong Provincial Engineering Technology Research Center of Seafood, Zhanjiang, 524088, China
- Collaborative Innovation Center of Seafood Deep Processing, Dalian Polytechnic University, Dalian, 116034, China
| | - Kuntai Li
- College of Food Science and Technology Guangdong Provincial Key Laboratory of Aquatic Product Processing and Safety Guangdong Province Engineering Laboratory for Marine Biological Products, Key Laboratory of Advanced Processing of Aquatic Product of Guangdong Higher Education Institution, Guangdong Ocean University, Guangdong Provincial Engineering Technology Research Center of Seafood, Zhanjiang, 524088, China.
- Collaborative Innovation Center of Seafood Deep Processing, Dalian Polytechnic University, Dalian, 116034, China.
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12
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Pacheco PJ, Cabrera JJ, Jiménez-Leiva A, Torres MJ, Gates AJ, Bedmar EJ, Richardson DJ, Mesa S, Tortosa G, Delgado MJ. The copper-responsive regulator CsoR is indirectly involved in Bradyrhizobium diazoefficiens denitrification. FEMS Microbiol Lett 2023; 370:fnad084. [PMID: 37573143 PMCID: PMC10457146 DOI: 10.1093/femsle/fnad084] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2023] [Revised: 08/04/2023] [Accepted: 08/11/2023] [Indexed: 08/14/2023] Open
Abstract
The soybean endosymbiont Bradyrhizobium diazoefficiens harbours the complete denitrification pathway that is catalysed by a periplasmic nitrate reductase (Nap), a copper (Cu)-containing nitrite reductase (NirK), a c-type nitric oxide reductase (cNor), and a nitrous oxide reductase (Nos), encoded by the napEDABC, nirK, norCBQD, and nosRZDFYLX genes, respectively. Induction of denitrification genes requires low oxygen and nitric oxide, both signals integrated into a complex regulatory network comprised by two interconnected cascades, FixLJ-FixK2-NnrR and RegSR-NifA. Copper is a cofactor of NirK and Nos, but it has also a role in denitrification gene expression and protein synthesis. In fact, Cu limitation triggers a substantial down-regulation of nirK, norCBQD, and nosRZDFYLX gene expression under denitrifying conditions. Bradyrhizobium diazoefficiens genome possesses a gene predicted to encode a Cu-responsive repressor of the CsoR family, which is located adjacent to copA, a gene encoding a putative Cu+-ATPase transporter. To investigate the role of CsoR in the control of denitrification gene expression in response to Cu, a csoR deletion mutant was constructed in this work. Mutation of csoR did not affect the capacity of B. diazoefficiens to grow under denitrifying conditions. However, by using qRT-PCR analyses, we showed that nirK and norCBQD expression was much lower in the csoR mutant compared to wild-type levels under Cu-limiting denitrifying conditions. On the contrary, copA expression was significantly increased in the csoR mutant. The results obtained suggest that CsoR acts as a repressor of copA. Under Cu limitation, CsoR has also an indirect role in the expression of nirK and norCBQD genes.
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Affiliation(s)
- Pedro J Pacheco
- Department of Soil and Plant Microbiology, Estación Experimental del Zaidín, CSIC, C/Profesor Albareda 1, E-18008 Granada, Spain
| | - Juan J Cabrera
- Department of Soil and Plant Microbiology, Estación Experimental del Zaidín, CSIC, C/Profesor Albareda 1, E-18008 Granada, Spain
| | - Andrea Jiménez-Leiva
- Department of Soil and Plant Microbiology, Estación Experimental del Zaidín, CSIC, C/Profesor Albareda 1, E-18008 Granada, Spain
| | - María J Torres
- School of Biological Sciences, University of East Anglia, Norwich Research Park, Colney Lane, Norwich NR4 7TJ, United Kingdom
- Department of Biochemistry and Molecular Biology, Campus Universitario de Rabanales, University of Córdoba, Ed. C6, Planta Baja, 14071 Córdoba, Spain
| | - Andrew J Gates
- School of Biological Sciences, University of East Anglia, Norwich Research Park, Colney Lane, Norwich NR4 7TJ, United Kingdom
| | - Eulogio J Bedmar
- Department of Soil and Plant Microbiology, Estación Experimental del Zaidín, CSIC, C/Profesor Albareda 1, E-18008 Granada, Spain
| | - David J Richardson
- School of Biological Sciences, University of East Anglia, Norwich Research Park, Colney Lane, Norwich NR4 7TJ, United Kingdom
| | - Socorro Mesa
- Department of Soil and Plant Microbiology, Estación Experimental del Zaidín, CSIC, C/Profesor Albareda 1, E-18008 Granada, Spain
| | - Germán Tortosa
- Department of Soil and Plant Microbiology, Estación Experimental del Zaidín, CSIC, C/Profesor Albareda 1, E-18008 Granada, Spain
| | - María J Delgado
- Department of Soil and Plant Microbiology, Estación Experimental del Zaidín, CSIC, C/Profesor Albareda 1, E-18008 Granada, Spain
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13
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Li Y, Zou N, Liang X, Zhou X, Guo S, Wang Y, Qin X, Tian Y, Lin J. Effects of nitrogen input on soil bacterial community structure and soil nitrogen cycling in the rhizosphere soil of Lycium barbarum L. Front Microbiol 2023; 13:1070817. [PMID: 36704567 PMCID: PMC9871820 DOI: 10.3389/fmicb.2022.1070817] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2022] [Accepted: 12/14/2022] [Indexed: 01/11/2023] Open
Abstract
Lycium barbarum L., goji berry, is a precious traditional Chinese medicine and it is homology of medicine and food. Its growth is heavily dependent on nitrogen. The use of chemical fertilizers has significantly promoted the yield of goji berry and the development of the L. barbarum L. industry. However, crop plants are inefficient in the acquisition and utilization of applied nitrogen, it often leads to excessive application of nitrogen fertilizers by producers, which cause negatively impact to the environment ultimately. The exploration of an interaction model which deals with crops, chemical fertilizers, and rhizosphere microbes to improve nitrogen use efficiency, is, therefore, an important research objective to achieve sustainable development of agriculture greatly. In our study, we explored the effects of nitrogen input on soil microbial community structure, soil nitrogen cycling, and the contents of nutrients in L. barbarum fruits. The structure and composition of the bacterial community in the rhizosphere soil of L. barbarum were significantly different under different nitrogen supply conditions, and high nitrogen addition inhibited the diversity and stability of bacterial communities. Low nitrogen input stimulated the relative abundance of ammonia-oxidizing bacteria (AOB), such as Nitrosospira, catalyzing the first step of the ammonia oxidation process. The results of the GLMM model showed that the level of nitrogen fertilizer (urea) input, the relative abundance of AOB, the relative abundance of Bradyrhizobium, and their combinations had significant effects on the soil nitrogen cycling and contents of nutrients in L. barbarum fruits. Therefore, we believe that moderately reducing the use of urea and other nitrogen fertilizers is more conducive to improving soil nitrogen use efficiency and Goji berry fruit quality by increasing the nitrogen cycling potential of soil microorganisms.
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Affiliation(s)
- Yuekun Li
- National Wolfberry Engineering Research Center, Wolfberry Science Research Institute, Ningxia Academy of Agriculture and Forestry Sciences, Yinchuan, China,*Correspondence: Yuekun Li, ✉
| | - Nan Zou
- Shandong Provincial Key Laboratory for Biology of Vegetable Diseases and Insect Pests, College of Plant Protection, Shandong Agricultural University, Taian, China
| | - Xiaojie Liang
- National Wolfberry Engineering Research Center, Wolfberry Science Research Institute, Ningxia Academy of Agriculture and Forestry Sciences, Yinchuan, China
| | - Xuan Zhou
- National Wolfberry Engineering Research Center, Wolfberry Science Research Institute, Ningxia Academy of Agriculture and Forestry Sciences, Yinchuan, China
| | - Shuhan Guo
- Shandong Provincial Key Laboratory for Biology of Vegetable Diseases and Insect Pests, College of Plant Protection, Shandong Agricultural University, Taian, China
| | - Yajun Wang
- National Wolfberry Engineering Research Center, Wolfberry Science Research Institute, Ningxia Academy of Agriculture and Forestry Sciences, Yinchuan, China
| | - Xiaoya Qin
- National Wolfberry Engineering Research Center, Wolfberry Science Research Institute, Ningxia Academy of Agriculture and Forestry Sciences, Yinchuan, China
| | - Yehan Tian
- Shandong Provincial Key Laboratory for Biology of Vegetable Diseases and Insect Pests, College of Plant Protection, Shandong Agricultural University, Taian, China
| | - Jin Lin
- Shandong Provincial Key Laboratory for Biology of Vegetable Diseases and Insect Pests, College of Plant Protection, Shandong Agricultural University, Taian, China,Jin Lin, ✉
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14
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Behrendt U, Spanner T, Augustin J, Zak DH, Horn MA, Kolb S, Ulrich A. Consumption of N2O by Flavobacterium azooxidireducens sp. nov. Isolated from Decomposing Leaf Litter of Phragmites australis (Cav.). Microorganisms 2022; 10:microorganisms10112304. [PMID: 36422374 PMCID: PMC9697520 DOI: 10.3390/microorganisms10112304] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2022] [Revised: 11/08/2022] [Accepted: 11/10/2022] [Indexed: 11/23/2022] Open
Abstract
Microorganisms acting as sinks for the greenhouse gas nitrous oxide (N2O) are gaining increasing attention in the development of strategies to control N2O emissions. Non-denitrifying N2O reducers are of particular interest because they can provide a real sink without contributing to N2O release. The bacterial strain under investigation (IGB 4-14T), isolated in a mesocosm experiment to study the litter decomposition of Phragmites australis (Cav.), is such an organism. It carries only a nos gene cluster with the sec-dependent Clade II nosZ and is able to consume significant amounts of N2O under anoxic conditions. However, consumption activity is considerably affected by the O2 level. The reduction of N2O was not associated with cell growth, suggesting that no energy is conserved by anaerobic respiration. Therefore, the N2O consumption of strain IGB 4-14T rather serves as an electron sink for metabolism to sustain viability during transient anoxia and/or to detoxify high N2O concentrations. Phylogenetic analysis of 16S rRNA gene similarity revealed that the strain belongs to the genus Flavobacterium. It shares a high similarity in the nos gene cluster composition and the amino acid similarity of the nosZ gene with various type strains of the genus. However, phylogenomic analysis and comparison of overall genome relatedness indices clearly demonstrated a novel species status of strain IGB 4-14T, with Flavobacterium lacus being the most closely related species. Various phenotypic differences supported a demarcation from this species. Based on these results, we proposed a novel species Flavobacterium azooxidireducens sp. nov. (type strain IGB 4-14T = LMG 29709T = DSM 103580T).
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Affiliation(s)
- Undine Behrendt
- Leibniz Centre for Agricultural Landscape Research (ZALF), Eberswalder Str. 84, D-15374 Müncheberg, Germany
- Correspondence: (U.B.); (A.U.); Tel.: +49-33432-82460 (U.B.); +49-33432-82345 (A.U.)
| | - Tobias Spanner
- Institute of Microbiology, Leibniz University Hannover, Herrenhäuser Str. 2, D-30419 Hannover, Germany
| | - Jürgen Augustin
- Leibniz Centre for Agricultural Landscape Research (ZALF), Eberswalder Str. 84, D-15374 Müncheberg, Germany
| | - Dominik H. Zak
- Institute for Ecoscience, Aarhus University, C.F. Møllersvej, Bygning 1331, 8000 Aarhus, Denmark
- Leibniz-Institute of Freshwater Ecology and Inland Fisheries Berlin, Müggelseedamm 301, D-12587 Berlin, Germany
| | - Marcus A. Horn
- Institute of Microbiology, Leibniz University Hannover, Herrenhäuser Str. 2, D-30419 Hannover, Germany
| | - Steffen Kolb
- Leibniz Centre for Agricultural Landscape Research (ZALF), Eberswalder Str. 84, D-15374 Müncheberg, Germany
| | - Andreas Ulrich
- Leibniz Centre for Agricultural Landscape Research (ZALF), Eberswalder Str. 84, D-15374 Müncheberg, Germany
- Correspondence: (U.B.); (A.U.); Tel.: +49-33432-82460 (U.B.); +49-33432-82345 (A.U.)
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15
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Müller C, Zhang L, Zipfel S, Topitsch A, Lutz M, Eckert J, Prasser B, Chami M, Lü W, Du J, Einsle O. Molecular interplay of an assembly machinery for nitrous oxide reductase. Nature 2022; 608:626-631. [PMID: 35896743 DOI: 10.1038/s41586-022-05015-2] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2021] [Accepted: 06/23/2022] [Indexed: 11/09/2022]
Abstract
Emissions of the critical ozone-depleting and greenhouse gas nitrous oxide (N2O) from soils and industrial processes have increased considerably over the last decades1-3. As the final step of bacterial denitrification, N2O is reduced to chemically inert N2 (refs. 1,4) in a reaction that is catalysed by the copper-dependent nitrous oxide reductase (N2OR) (ref. 5). The assembly of its unique [4Cu:2S] active site cluster CuZ requires both the ATP-binding-cassette (ABC) complex NosDFY and the membrane-anchored copper chaperone NosL (refs. 4,6). Here we report cryo-electron microscopy structures of Pseudomonas stutzeri NosDFY and its complexes with NosL and N2OR, respectively. We find that the periplasmic NosD protein contains a binding site for a Cu+ ion and interacts specifically with NosL in its nucleotide-free state, whereas its binding to N2OR requires a conformational change that is triggered by ATP binding. Mutually exclusive structures of NosDFY in complex with NosL and with N2OR reveal a sequential metal-trafficking and assembly pathway for a highly complex copper site. Within this pathway, NosDFY acts as a mechanical energy transducer rather than as a transporter. It links ATP hydrolysis in the cytoplasm to a conformational transition of the NosD subunit in the periplasm, which is required for NosDFY to switch its interaction partner so that copper ions are handed over from the chaperone NosL to the enzyme N2OR.
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Affiliation(s)
- Christoph Müller
- Institut für Biochemie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Lin Zhang
- Institut für Biochemie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Sara Zipfel
- Institut für Biochemie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Annika Topitsch
- Institut für Biochemie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Marleen Lutz
- Institut für Biochemie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Johannes Eckert
- Institut für Biochemie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Benedikt Prasser
- Institut für Biochemie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Mohamed Chami
- BioEM Lab, Biozentrum, Universität Basel, Basel, Switzerland
| | - Wei Lü
- Department of Structural Biology, Van Andel Institute, Grand Rapids, MI, USA
| | - Juan Du
- Department of Structural Biology, Van Andel Institute, Grand Rapids, MI, USA.
| | - Oliver Einsle
- Institut für Biochemie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany.
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16
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Parejo S, Cabrera JJ, Jiménez-Leiva A, Tomás-Gallardo L, Bedmar EJ, Gates AJ, Mesa S. Fine-Tuning Modulation of Oxidation-Mediated Posttranslational Control of Bradyrhizobium diazoefficiens FixK 2 Transcription Factor. Int J Mol Sci 2022; 23:5117. [PMID: 35563511 PMCID: PMC9104804 DOI: 10.3390/ijms23095117] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2022] [Revised: 04/22/2022] [Accepted: 04/29/2022] [Indexed: 02/04/2023] Open
Abstract
FixK2 is a CRP/FNR-type transcription factor that plays a central role in a sophisticated regulatory network for the anoxic, microoxic and symbiotic lifestyles of the soybean endosymbiont Bradyrhizobium diazoefficiens. Aside from the balanced expression of the fixK2 gene under microoxic conditions (induced by the two-component regulatory system FixLJ and negatively auto-repressed), FixK2 activity is posttranslationally controlled by proteolysis, and by the oxidation of a singular cysteine residue (C183) near its DNA-binding domain. To simulate the permanent oxidation of FixK2, we replaced C183 for aspartic acid. Purified C183D FixK2 protein showed both low DNA binding and in vitro transcriptional activation from the promoter of the fixNOQP operon, required for respiration under symbiosis. However, in a B. diazoefficiens strain coding for C183D FixK2, expression of a fixNOQP'-'lacZ fusion was similar to that in the wild type, when both strains were grown microoxically. The C183D FixK2 encoding strain also showed a wild-type phenotype in symbiosis with soybeans, and increased fixK2 gene expression levels and FixK2 protein abundance in cells. These two latter observations, together with the global transcriptional profile of the microoxically cultured C183D FixK2 encoding strain, suggest the existence of a finely tuned regulatory strategy to counterbalance the oxidation-mediated inactivation of FixK2 in vivo.
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Affiliation(s)
- Sergio Parejo
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, CSIC, 18008 Granada, Spain; (S.P.); (J.J.C.); (A.J.-L.); (E.J.B.)
| | - Juan J. Cabrera
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, CSIC, 18008 Granada, Spain; (S.P.); (J.J.C.); (A.J.-L.); (E.J.B.)
| | - Andrea Jiménez-Leiva
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, CSIC, 18008 Granada, Spain; (S.P.); (J.J.C.); (A.J.-L.); (E.J.B.)
| | - Laura Tomás-Gallardo
- Proteomics and Biochemistry Unit, Andalusian Centre for Developmental Biology, CSIC-Pablo de Olavide University, 41013 Seville, Spain;
| | - Eulogio J. Bedmar
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, CSIC, 18008 Granada, Spain; (S.P.); (J.J.C.); (A.J.-L.); (E.J.B.)
| | - Andrew J. Gates
- School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK;
| | - Socorro Mesa
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, CSIC, 18008 Granada, Spain; (S.P.); (J.J.C.); (A.J.-L.); (E.J.B.)
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17
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Pacheco PJ, Cabrera JJ, Jiménez-Leiva A, Bedmar EJ, Mesa S, Tortosa G, Delgado MJ. Effect of Copper on Expression of Functional Genes and Proteins Associated with Bradyrhizobium diazoefficiens Denitrification. Int J Mol Sci 2022; 23:ijms23063386. [PMID: 35328804 PMCID: PMC8951191 DOI: 10.3390/ijms23063386] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2022] [Revised: 03/16/2022] [Accepted: 03/17/2022] [Indexed: 12/16/2022] Open
Abstract
Nitrous oxide (N2O) is a powerful greenhouse gas that contributes to climate change. Denitrification is one of the largest sources of N2O in soils. The soybean endosymbiont Bradyrhizobium diazoefficiens is a model for rhizobial denitrification studies since, in addition to fixing N2, it has the ability to grow anaerobically under free-living conditions by reducing nitrate from the medium through the complete denitrification pathway. This bacterium contains a periplasmic nitrate reductase (Nap), a copper (Cu)-containing nitrite reductase (NirK), a c-type nitric oxide reductase (cNor), and a Cu-dependent nitrous oxide reductase (Nos) encoded by the napEDABC, nirK, norCBQD and nosRZDFYLX genes, respectively. In this work, an integrated study of the role of Cu in B. diazoefficiens denitrification has been performed. A notable reduction in nirK, nor, and nos gene expression observed under Cu limitation was correlated with a significant decrease in NirK, NorC and NosZ protein levels and activities. Meanwhile, nap expression was not affected by Cu, but a remarkable depletion in Nap activity was found, presumably due to an inhibitory effect of nitrite accumulated under Cu-limiting conditions. Interestingly, a post-transcriptional regulation by increasing Nap and NirK activities, as well as NorC and NosZ protein levels, was observed in response to high Cu. Our results demonstrate, for the first time, the role of Cu in transcriptional and post-transcriptional control of B. diazoefficiens denitrification. Thus, this study will contribute by proposing useful strategies for reducing N2O emissions from agricultural soils.
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18
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Bueno E, Mania D, Mesa S, Bedmar EJ, Frostegård Å, Bakken LR, Delgado MJ. Regulation of the Emissions of the Greenhouse Gas Nitrous Oxide by the Soybean Endosymbiont Bradyrhizobium diazoefficiens. Int J Mol Sci 2022; 23:1486. [PMID: 35163408 PMCID: PMC8836242 DOI: 10.3390/ijms23031486] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2021] [Revised: 01/20/2022] [Accepted: 01/20/2022] [Indexed: 11/21/2022] Open
Abstract
The greenhouse gas nitrous oxide (N2O) has strong potential to drive climate change. Soils are a major source of N2O, with microbial nitrification and denitrification being the primary processes involved in such emissions. The soybean endosymbiont Bradyrhizobium diazoefficiens is a model microorganism to study denitrification, a process that depends on a set of reductases, encoded by the napEDABC, nirK, norCBQD, and nosRZDYFLX genes, which sequentially reduce nitrate (NO3-) to nitrite (NO2-), nitric oxide (NO), N2O, and dinitrogen (N2). In this bacterium, the regulatory network and environmental cues governing the expression of denitrification genes rely on the FixK2 and NnrR transcriptional regulators. To understand the role of FixK2 and NnrR proteins in N2O turnover, we monitored real-time kinetics of NO3-, NO2-, NO, N2O, N2, and oxygen (O2) in a fixK2 and nnrR mutant using a robotized incubation system. We confirmed that FixK2 and NnrR are regulatory determinants essential for NO3- respiration and N2O reduction. Furthermore, we demonstrated that N2O reduction by B. diazoefficiens is independent of canonical inducers of denitrification, such as the nitrogen oxide NO3-, and it is negatively affected by acidic and alkaline conditions. These findings advance the understanding of how specific environmental conditions and two single regulators modulate N2O turnover in B. diazoefficiens.
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Affiliation(s)
- Emilio Bueno
- Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, 18008 Granada, Spain; (S.M.); (E.J.B.)
| | - Daniel Mania
- Faculty of Chemistry, Biotechnology and Food Sciences, Norwegian University of Life Sciences, P.O. Box 5003, N-1432 Aas, Norway; (D.M.); (Å.F.); (L.R.B.)
| | - Socorro Mesa
- Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, 18008 Granada, Spain; (S.M.); (E.J.B.)
| | - Eulogio J. Bedmar
- Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, 18008 Granada, Spain; (S.M.); (E.J.B.)
| | - Åsa Frostegård
- Faculty of Chemistry, Biotechnology and Food Sciences, Norwegian University of Life Sciences, P.O. Box 5003, N-1432 Aas, Norway; (D.M.); (Å.F.); (L.R.B.)
| | - Lars R. Bakken
- Faculty of Chemistry, Biotechnology and Food Sciences, Norwegian University of Life Sciences, P.O. Box 5003, N-1432 Aas, Norway; (D.M.); (Å.F.); (L.R.B.)
| | - María J. Delgado
- Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, 18008 Granada, Spain; (S.M.); (E.J.B.)
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19
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Sixteen Genome Sequences of Denitrifying Bacteria Assembled from Enriched Cultures of Anaerobic Pig Manure Digestate. Microbiol Resour Announc 2021; 10:e0078221. [PMID: 34591671 PMCID: PMC8483710 DOI: 10.1128/mra.00782-21] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We report 16 genomes assembled from the metagenome of pig manure digestate enriched with the addition of N2O. These denitrifying bacterial genomes all contain the nosZ gene, encoding N2O reductase. Their sizes range from 1,902,599 bp to 6,264,563 bp, with completeness of 75.03% to 98.89%, GC contents of 32.86% to 69.66%, and contamination of 0% to 8.4%.
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20
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Schnabel U, Balazinski M, Wagner R, Stachowiak J, Boehm D, Andrasch M, Bourke P, Ehlbeck J. Optimizing the application of plasma functionalised water (PFW) for microbial safety in fresh-cut endive processing. INNOV FOOD SCI EMERG 2021. [DOI: 10.1016/j.ifset.2021.102745] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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21
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Cabrera JJ, Jiménez-Leiva A, Tomás-Gallardo L, Parejo S, Casado S, Torres MJ, Bedmar EJ, Delgado MJ, Mesa S. Dissection of FixK 2 protein-DNA interaction unveils new insights into Bradyrhizobium diazoefficiens lifestyles control. Environ Microbiol 2021; 23:6194-6209. [PMID: 34227211 DOI: 10.1111/1462-2920.15661] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2021] [Revised: 07/01/2021] [Accepted: 07/03/2021] [Indexed: 11/28/2022]
Abstract
The FixK2 protein plays a pivotal role in a complex regulatory network, which controls genes for microoxic, denitrifying, and symbiotic nitrogen-fixing lifestyles in Bradyrhizobium diazoefficiens. Among the microoxic-responsive FixK2 -activated genes are the fixNOQP operon, indispensable for respiration in symbiosis, and the nnrR regulatory gene needed for the nitric-oxide dependent induction of the norCBQD genes encoding the denitrifying nitric oxide reductase. FixK2 is a CRP/FNR-type transcription factor, which recognizes a 14 bp-palindrome (FixK2 box) at the regulated promoters through three residues (L195, E196, and R200) within a C-terminal helix-turn-helix motif. Here, we mapped the determinants for discriminatory FixK2 -mediated regulation. While R200 was essential for DNA binding and activity of FixK2 , L195 was involved in protein-DNA complex stability. Mutation at positions 1, 3, or 11 in the genuine FixK2 box at the fixNOQP promoter impaired transcription activation by FixK2 , which was residual when a second mutation affecting the box palindromy was introduced. The substitution of nucleotide 11 within the NnrR box at the norCBQD promoter allowed FixK2 -mediated activation in response to microoxia. Thus, position 11 within the FixK2 /NnrR boxes constitutes a key element that changes FixK2 targets specificity, and consequently, it might modulate B. diazoefficiens lifestyle as nitrogen fixer or as denitrifier.
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Affiliation(s)
- Juan J Cabrera
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, CSIC, Granada, 18008, Spain
| | - Andrea Jiménez-Leiva
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, CSIC, Granada, 18008, Spain
| | - Laura Tomás-Gallardo
- Proteomics and Biochemistry Unit, Andalusian Centre for Developmental Biology, CSIC-Junta de Andalucía-Pablo de Olavide University, Seville, 41013, Spain
| | - Sergio Parejo
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, CSIC, Granada, 18008, Spain
| | - Sara Casado
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, CSIC, Granada, 18008, Spain
| | - María J Torres
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, CSIC, Granada, 18008, Spain
| | - Eulogio J Bedmar
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, CSIC, Granada, 18008, Spain
| | - María J Delgado
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, CSIC, Granada, 18008, Spain
| | - Socorro Mesa
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, CSIC, Granada, 18008, Spain
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22
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Salas A, Cabrera JJ, Jiménez-Leiva A, Mesa S, Bedmar EJ, Richardson DJ, Gates AJ, Delgado MJ. Bacterial nitric oxide metabolism: Recent insights in rhizobia. Adv Microb Physiol 2021; 78:259-315. [PMID: 34147187 DOI: 10.1016/bs.ampbs.2021.05.001] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Nitric oxide (NO) is a reactive gaseous molecule that has several functions in biological systems depending on its concentration. At low concentrations, NO acts as a signaling molecule, while at high concentrations, it becomes very toxic due to its ability to react with multiple cellular targets. Soil bacteria, commonly known as rhizobia, have the capacity to establish a N2-fixing symbiosis with legumes inducing the formation of nodules in their roots. Several reports have shown NO production in the nodules where this gas acts either as a signaling molecule which regulates gene expression, or as a potent inhibitor of nitrogenase and other plant and bacteria enzymes. A better understanding of the sinks and sources of NO in rhizobia is essential to protect symbiotic nitrogen fixation from nitrosative stress. In nodules, both the plant and the microsymbiont contribute to the production of NO. From the bacterial perspective, the main source of NO reported in rhizobia is the denitrification pathway that varies significantly depending on the species. In addition to denitrification, nitrate assimilation is emerging as a new source of NO in rhizobia. To control NO accumulation in the nodules, in addition to plant haemoglobins, bacteroids also contribute to NO detoxification through the expression of a NorBC-type nitric oxide reductase as well as rhizobial haemoglobins. In the present review, updated knowledge about the NO metabolism in legume-associated endosymbiotic bacteria is summarized.
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Affiliation(s)
- Ana Salas
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Granada, Spain
| | - Juan J Cabrera
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Granada, Spain; School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich, United Kingdom
| | - Andrea Jiménez-Leiva
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Granada, Spain
| | - Socorro Mesa
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Granada, Spain
| | - Eulogio J Bedmar
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Granada, Spain
| | - David J Richardson
- School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich, United Kingdom
| | - Andrew J Gates
- School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich, United Kingdom
| | - María J Delgado
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Granada, Spain.
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23
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Carreira C, Nunes RF, Mestre O, Moura I, Pauleta SR. The effect of pH on Marinobacter hydrocarbonoclasticus denitrification pathway and nitrous oxide reductase. J Biol Inorg Chem 2020; 25:927-940. [PMID: 32851479 DOI: 10.1007/s00775-020-01812-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2020] [Accepted: 08/12/2020] [Indexed: 11/27/2022]
Abstract
Increasing atmospheric concentration of N2O has been a concern, as it is a potent greenhouse gas and promotes ozone layer destruction. In the N-cycle, release of N2O is boosted upon a drop of pH in the environment. Here, Marinobacter hydrocarbonoclasticus was grown in batch mode in the presence of nitrate, to study the effect of pH in the denitrification pathway by gene expression profiling, quantification of nitrate and nitrite, and evaluating the ability of whole cells to reduce NO and N2O. At pH 6.5, accumulation of nitrite in the medium occurs and the cells were unable to reduce N2O. In addition, the biochemical properties of N2O reductase isolated from cells grown at pH 6.5, 7.5 and 8.5 were compared for the first time. The amount of this enzyme at acidic pH was lower than that at pH 7.5 and 8.5, pinpointing to a post-transcriptional regulation, though pH did not affect gene expression of N2O reductase accessory genes. N2O reductase isolated from cells grown at pH 6.5 has its catalytic center mainly as CuZ(4Cu1S), while that from cells grown at pH 7.5 or 8.5 has it as CuZ(4Cu2S). This study evidences that an in vivo secondary level of regulation is required to maintain N2O reductase in an active state.
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Affiliation(s)
- Cíntia Carreira
- Microbial Stress Lab, UCIBIO, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus da Caparica, 2829-516, Caparica, Portugal
- Biological Chemistry Lab, LAQV, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus da Caparica, 2829-516, Caparica, Portugal
| | - Rute F Nunes
- Microbial Stress Lab, UCIBIO, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus da Caparica, 2829-516, Caparica, Portugal
| | - Olga Mestre
- Microbial Stress Lab, UCIBIO, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus da Caparica, 2829-516, Caparica, Portugal
| | - Isabel Moura
- Biological Chemistry Lab, LAQV, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus da Caparica, 2829-516, Caparica, Portugal
| | - Sofia R Pauleta
- Microbial Stress Lab, UCIBIO, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus da Caparica, 2829-516, Caparica, Portugal.
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24
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Pascual MB, Sánchez-Monedero MÁ, Cayuela ML, Li S, Haderlein SB, Ruser R, Kappler A. Biochar as electron donor for reduction of N2O by Paracoccus denitrificans. FEMS Microbiol Ecol 2020; 96:fiaa133. [PMID: 32602887 PMCID: PMC7360485 DOI: 10.1093/femsec/fiaa133] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2020] [Accepted: 06/29/2020] [Indexed: 11/13/2022] Open
Abstract
Biochar (BC) has been shown to influence microbial denitrification and mitigate soil N2O emissions. However, it is unclear if BC is able to directly stimulate the microbial reduction of N2O to N2. We hypothesized that the ability of BC to lower N2O emissions could be related not only to its ability to store electrons, but to donate them to bacteria that enzymatically reduce N2O. Therefore, we carried out anoxic incubations with Paracoccus denitrificans, known amounts of N2O, and nine contrasting BCs, in the absence of any other electron donor or acceptor. We found a strong and direct correlation between the extent and rates of N2O reduction with BC's EDC/EEC (electron donating capacity/electron exchange capacity). Apart from the redox capacity, other BC properties were found to regulate the BC's ability to increase N2O reduction by P. denitrificans. For this specific BC series, we found that a high H/C and ash content, low surface area and poor lignin feedstocks favored N2O reduction. This provides valuable information for producing tailored BCs with the potential to assist and promote the reduction of N2O in the pursuit of reducing this greenhouse gas emissions.
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Affiliation(s)
- Mª Blanca Pascual
- Department of Soil and Water Conservation and Waste Management, Centro de Edafología y Biología Aplicada del Segura (CEBAS-CSIC), Campus Universitario de Espinardo 30100 Murcia, Spain
- Geomicrobiology, Center for Applied Geosciences, University of Tübingen, Sigwartstrasse 10, 72074 Tübingen, Germany
| | - Miguel Ángel Sánchez-Monedero
- Department of Soil and Water Conservation and Waste Management, Centro de Edafología y Biología Aplicada del Segura (CEBAS-CSIC), Campus Universitario de Espinardo 30100 Murcia, Spain
| | - María L Cayuela
- Department of Soil and Water Conservation and Waste Management, Centro de Edafología y Biología Aplicada del Segura (CEBAS-CSIC), Campus Universitario de Espinardo 30100 Murcia, Spain
| | - Shun Li
- Environmental Mineralogy and Chemistry, Center for Applied Geosciences, University of Tübingen, Sigwartstrasse 10, 72074 Tübingen, Germany
| | - Stefan B Haderlein
- Environmental Mineralogy and Chemistry, Center for Applied Geosciences, University of Tübingen, Sigwartstrasse 10, 72074 Tübingen, Germany
| | - Reiner Ruser
- Institute of Crop Science, Department of Fertilization and Soil Matter Dynamics, University of Hohenheim, Fruwirthstraβe 20, 70599 Stuttgart, Germany
| | - Andreas Kappler
- Geomicrobiology, Center for Applied Geosciences, University of Tübingen, Sigwartstrasse 10, 72074 Tübingen, Germany
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25
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Salas A, Tortosa G, Hidalgo-García A, Delgado A, Bedmar EJ, Richardson DJ, Gates AJ, Delgado MJ. The Hemoglobin Bjgb From Bradyrhizobium diazoefficiens Controls NO Homeostasis in Soybean Nodules to Protect Symbiotic Nitrogen Fixation. Front Microbiol 2020; 10:2915. [PMID: 31998252 PMCID: PMC6965051 DOI: 10.3389/fmicb.2019.02915] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2019] [Accepted: 12/03/2019] [Indexed: 11/13/2022] Open
Abstract
Legume-rhizobia symbiotic associations have beneficial effects on food security and nutrition, health and climate change. Hypoxia induced by flooding produces nitric oxide (NO) in nodules from soybean plants cultivated in nitrate-containing soils. As NO is a strong inhibitor of nitrogenase expression and activity, this negatively impacts symbiotic nitrogen fixation in soybean and limits crop production. In Bradyrhizobium diazoefficiens, denitrification is the main process involved in NO formation by soybean flooded nodules. In addition to denitrification, nitrate assimilation is another source of NO in free-living B. diazoefficiens cells and a single domain hemoglobin (Bjgb) has been shown to have a role in NO detoxification during nitrate-dependent growth. However, the involvement of Bjgb in protecting nitrogenase against NO in soybean nodules remains unclear. In this work, we have investigated the effect of inoculation of soybean plants with a bjgb mutant on biological nitrogen fixation. By analyzing the proportion of N in shoots derived from N2-fixation using the 15N isotope dilution technique, we found that plants inoculated with the bjgb mutant strain had higher tolerance to flooding than those inoculated with the parental strain. Similarly, reduction of nitrogenase activity and nifH expression by flooding was less pronounced in bjgb than in WT nodules. These beneficial effects are probably due to the reduction of NO accumulation in bjgb flooded nodules compared to the wild-type nodules. This decrease is caused by an induction of expression and activity of the denitrifying NO reductase enzyme in bjgb bacteroids. As bjgb deficiency promotes NO-tolerance, the negative effect of NO on nitrogenase is partially prevented and thus demonstrates that inoculation of soybean plants with the B. diazoefficiens bjgb mutant confers protection of symbiotic nitrogen fixation during flooding.
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Affiliation(s)
- Ana Salas
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Granada, Spain
| | - Germán Tortosa
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Granada, Spain
| | - Alba Hidalgo-García
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Granada, Spain
| | - Antonio Delgado
- Laboratory of Stable Isotopes Biogeochemistry, Instituto Andaluz de Ciencias de la Tierra, Consejo Superior de Investigaciones Científicas, Granada, Spain
| | - Eulogio J Bedmar
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Granada, Spain
| | - David J Richardson
- School of Biological Sciences, University of East Anglia, Norwich, United Kingdom
| | - Andrew J Gates
- School of Biological Sciences, University of East Anglia, Norwich, United Kingdom
| | - María J Delgado
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Granada, Spain
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26
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Wang X, Duo Y, He J, Yao J, Qian H, Hrynsphan D, Tatsiana S, Chen J. A newly isolated and rapid denitrifier Pseudomonas citronellolis WXP-4: difference in N2O emissions under aerobic and anaerobic conditions. Bioprocess Biosyst Eng 2020; 43:811-820. [DOI: 10.1007/s00449-019-02276-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2019] [Accepted: 12/20/2019] [Indexed: 12/19/2022]
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27
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Assessment of Heterotrophic Nitrification Capacity in Bacillus spp. and its Potential Application in the Removal of Nitrogen from Aquaculture Water. JOURNAL OF PURE AND APPLIED MICROBIOLOGY 2019. [DOI: 10.22207/jpam.13.4.02] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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28
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Bacterial nitrous oxide respiration: electron transport chains and copper transfer reactions. Adv Microb Physiol 2019; 75:137-175. [PMID: 31655736 DOI: 10.1016/bs.ampbs.2019.07.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Biologically catalyzed nitrous oxide (N2O, laughing gas) reduction to dinitrogen gas (N2) is a desirable process in the light of ever-increasing atmospheric concentrations of this important greenhouse gas and ozone depleting substance. A diverse range of bacterial species produce the copper cluster-containing enzyme N2O reductase (NosZ), which is the only known enzyme that converts N2O to N2. Based on phylogenetic analyses, NosZ enzymes have been classified into clade I or clade II and it has turned out that this differentiation is also applicable to nos gene clusters (NGCs) and some physiological traits of the corresponding microbial cells. The NosZ enzyme is the terminal reductase of anaerobic N2O respiration, in which electrons derived from a donor substrate are transferred to NosZ by means of an electron transport chain (ETC) that conserves energy through proton motive force generation. This chapter presents models of the ETCs involved in clade I and clade II N2O respiration as well as of the respective NosZ maturation and maintenance processes. Despite differences in NGCs and growth yields of N2O-respiring microorganisms, the deduced bioenergetic framework in clade I and clade II N2O respiration is assumed to be equivalent. In both cases proton motive quinol oxidation by N2O is thought to be catalyzed by the Q cycle mechanism of a membrane-bound Rieske/cytochrome bc complex. However, clade I and clade II organisms are expected to differ significantly in terms of auxiliary electron transport processes as well as NosZ active site maintenance and repair.
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29
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Sánchez C, Minamisawa K. Nitrogen Cycling in Soybean Rhizosphere: Sources and Sinks of Nitrous Oxide (N 2O). Front Microbiol 2019; 10:1943. [PMID: 31497007 PMCID: PMC6712156 DOI: 10.3389/fmicb.2019.01943] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2019] [Accepted: 08/07/2019] [Indexed: 01/29/2023] Open
Abstract
Nitrous oxide (N2O) is the third most important greenhouse gas after carbon dioxide and methane, and a prominent ozone-depleting substance. Agricultural soils are the primary anthropogenic source of N2O because of the constant increase in the use of industrial nitrogen (N) fertilizers. The soybean crop is grown on 6% of the world's arable land, and its production is expected to increase rapidly in the future. In this review, we summarize the current knowledge on N-cycle in the rhizosphere of soybean plants, particularly sources and sinks of N2O. Soybean root nodules are the host of dinitrogen (N2)-fixing bacteria from the genus Bradyrhizobium. Nodule decomposition is the main source of N2O in soybean rhizosphere, where soil organisms mediate the nitrogen transformations that produce N2O. This N2O is either emitted into the atmosphere or further reduced to N2 by the bradyrhizobial N2O reductase (N2OR), encoded by the nos gene cluster. The dominance of nos - indigenous populations of soybean bradyrhizobia results in the emission of N2O into the atmosphere. Hence, inoculation with nos + or nos ++ (mutants with enhanced N2OR activity) bradyrhizobia has proved to be promising strategies to reduce N2O emission in the field. We discussed these strategies, the molecular mechanisms underlying them, and the future perspectives to develop better options for global mitigation of N2O emission from soils.
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Affiliation(s)
- Cristina Sánchez
- Graduate School of Life Sciences, Tohoku University, Sendai, Japan
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30
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Jiménez-Leiva A, Cabrera JJ, Bueno E, Torres MJ, Salazar S, Bedmar EJ, Delgado MJ, Mesa S. Expanding the Regulon of the Bradyrhizobium diazoefficiens NnrR Transcription Factor: New Insights Into the Denitrification Pathway. Front Microbiol 2019; 10:1926. [PMID: 31481951 PMCID: PMC6710368 DOI: 10.3389/fmicb.2019.01926] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2019] [Accepted: 08/05/2019] [Indexed: 12/02/2022] Open
Abstract
Denitrification in the soybean endosymbiont Bradyrhizobium diazoefficiens is controlled by a complex regulatory network composed of two hierarchical cascades, FixLJ-FixK2-NnrR and RegSR-NifA. In the former cascade, the CRP/FNR-type transcription factors FixK2 and NnrR exert disparate control on expression of core denitrifying systems encoded by napEDABC, nirK, norCBQD, and nosRZDFYLX genes in response to microoxia and nitrogen oxides, respectively. To identify additional genes controlled by NnrR and involved in the denitrification process in B. diazoefficiens, we compared the transcriptional profile of an nnrR mutant with that of the wild type, both grown under anoxic denitrifying conditions. This approach revealed more than 170 genes were simultaneously induced in the wild type and under the positive control of NnrR. Among them, we found the cycA gene which codes for the c550 soluble cytochrome (CycA), previously identified as an intermediate electron donor between the bc1 complex and the denitrifying nitrite reductase NirK. Here, we demonstrated that CycA is also required for nitrous oxide reductase activity. However, mutation in cycA neither affected nosZ gene expression nor NosZ protein steady-state levels. Furthermore, cycA, nnrR and its proximal divergently oriented nnrS gene, are direct targets for FixK2 as determined by in vitro transcription activation assays. The dependence of cycA expression on FixK2 and NnrR in anoxic denitrifying conditions was validated at transcriptional level, determined by quantitative reverse transcription PCR, and at the level of protein by performing heme c-staining of soluble cytochromes. Thus, this study expands the regulon of NnrR and demonstrates the role of CycA in the activity of the nitrous oxide reductase, the key enzyme for nitrous oxide mitigation.
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Affiliation(s)
- Andrea Jiménez-Leiva
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Granada, Spain
| | - Juan J Cabrera
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Granada, Spain
| | - Emilio Bueno
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Granada, Spain
| | - María J Torres
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Granada, Spain
| | - Sergio Salazar
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Granada, Spain
| | - Eulogio J Bedmar
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Granada, Spain
| | - María J Delgado
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Granada, Spain
| | - Socorro Mesa
- Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Granada, Spain
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Zhurakivska K, Troiano G, Caponio VCA, Dioguardi M, Laino L, Maffione AB, Lo Muzio L. Do Changes in Oral Microbiota Correlate With Plasma Nitrite Response? A Systematic Review. Front Physiol 2019; 10:1029. [PMID: 31456696 PMCID: PMC6700760 DOI: 10.3389/fphys.2019.01029] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2019] [Accepted: 07/25/2019] [Indexed: 01/20/2023] Open
Abstract
Background: Nitric Oxide (NO) has a role in immunitary defense, regulation of mucosal blood flow and mucus production, regulation of smooth muscle contraction, cerebral blood flow, glucose regulation, and mitochondrial function. NO can be synthetized endogenously through the L-arginine-NO pathway or it can be absorbed by the human intestine through the dietary intake. Most of the ingested NO is in the form of nitrate (NO3−). NO3− is a substrate of oral and intestinal microbiota and, at the end of the catabolic pathway, NO is released. Using antibacterial mouthwashes leads to an alteration of salivary NO3− metabolism, however, with unclear consequences on the circulating NO levels. The aim of this study is to perform a systematic review in order to elucidate if the alterations of oral microbiota lead to modifications in plasma NO content. Methods: Electronic databases were screened, using the following terms: [“oral bacteria” and (nitrate OR nitrite OR nitric)]. Clinical studies reporting NO3− and NO2− measurements in blood and their correlation to oral microbiota variations were included. We focused on the correlation between the changes in oral microbiota and plasma concentrations of nitrites (primary outcome). Subsequently, we investigated if modifications in oral microbiota could lead to changes in blood pressure and salivary NO2− concentration (secondary outcome). Results: Six studies, for a total of 82 participants were included in this review. In four studies, the use of mouthwash correlated to a reduction of plasma nitrite concentration (p < 0.05); Two studies did not find any difference in plasma nitrate or nitrite concentration. In five studies, a correlation between blood pressure (BP) changes and antibacterial mouthwashing emerged. Anyway, only three studies suggested a significant increase of systolic BP following mouthwashing compared with controls. Conclusions: Although, the role of oral bacteria has been unequivocally demonstrated in the regulation of salivary NO3− metabolism, their influence on plasma concentration of NO species remains ambiguous. Further studies with larger sample size are required in order to demonstrate if an alteration in oral microbiota composition may influence the blood content of NO3−/NO2−/NO and all the linked biological processes.
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Affiliation(s)
- Khrystyna Zhurakivska
- Department of Clinical and Experimental Medicine, University of Foggia, Foggia, Italy
| | - Giuseppe Troiano
- Department of Clinical and Experimental Medicine, University of Foggia, Foggia, Italy
| | | | - Mario Dioguardi
- Department of Clinical and Experimental Medicine, University of Foggia, Foggia, Italy
| | - Luigi Laino
- Multidisciplinary Department of Medical-Surgical and Odontostomatological Specialties, University of Campania "Luigi Vanvitelli", Naples, Italy
| | - Angela Bruna Maffione
- Department of Clinical and Experimental Medicine, University of Foggia, Foggia, Italy
| | - Lorenzo Lo Muzio
- Department of Clinical and Experimental Medicine, University of Foggia, Foggia, Italy
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Otte JM, Blackwell N, Ruser R, Kappler A, Kleindienst S, Schmidt C. N 2O formation by nitrite-induced (chemo)denitrification in coastal marine sediment. Sci Rep 2019; 9:10691. [PMID: 31366952 PMCID: PMC6668465 DOI: 10.1038/s41598-019-47172-x] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2018] [Accepted: 07/12/2019] [Indexed: 11/08/2022] Open
Abstract
Nitrous oxide (N2O) is a potent greenhouse gas that also contributes to stratospheric ozone depletion. Besides microbial denitrification, abiotic nitrite reduction by Fe(II) (chemodenitrification) has the potential to be an important source of N2O. Here, using microcosms, we quantified N2O formation in coastal marine sediments under typical summer temperatures. Comparison between gamma-radiated and microbially-active microcosm experiments revealed that at least 15-25% of total N2O formation was caused by chemodenitrification, whereas 75-85% of total N2O was potentially produced by microbial N-transformation processes. An increase in (chemo)denitrification-based N2O formation and associated Fe(II) oxidation caused an upregulation of N2O reductase (typical nosZ) genes and a distinct community shift to potential Fe(III)-reducers (Arcobacter), Fe(II)-oxidizers (Sulfurimonas), and nitrate/nitrite-reducing microorganisms (Marinobacter). Our study suggests that chemodenitrification contributes substantially to N2O formation from marine sediments and significantly influences the N- and Fe-cycling microbial community.
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Affiliation(s)
- Julia M Otte
- Geomicrobiology, Center for Applied Geosciences, University of Tübingen, Tübingen, Germany
- Microbial Ecology, Center for Applied Geosciences, University of Tübingen, Tübingen, Germany
| | - Nia Blackwell
- Geomicrobiology, Center for Applied Geosciences, University of Tübingen, Tübingen, Germany
- Microbial Ecology, Center for Applied Geosciences, University of Tübingen, Tübingen, Germany
| | - Reiner Ruser
- Fertilization and Soil Matter Dynamics, Institute of Crop Science, University of Hohenheim, Stuttgart, Germany
| | - Andreas Kappler
- Geomicrobiology, Center for Applied Geosciences, University of Tübingen, Tübingen, Germany.
- Center for Geomicrobiology, Aarhus University, Aarhus, Denmark.
| | - Sara Kleindienst
- Geomicrobiology, Center for Applied Geosciences, University of Tübingen, Tübingen, Germany
- Microbial Ecology, Center for Applied Geosciences, University of Tübingen, Tübingen, Germany
| | - Caroline Schmidt
- Geomicrobiology, Center for Applied Geosciences, University of Tübingen, Tübingen, Germany
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33
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Hidalgo-García A, Torres MJ, Salas A, Bedmar EJ, Girard L, Delgado MJ. Rhizobium etli Produces Nitrous Oxide by Coupling the Assimilatory and Denitrification Pathways. Front Microbiol 2019; 10:980. [PMID: 31134023 PMCID: PMC6514139 DOI: 10.3389/fmicb.2019.00980] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2018] [Accepted: 04/18/2019] [Indexed: 11/13/2022] Open
Abstract
More than two-thirds of the powerful greenhouse gas nitrous oxide (N2O) emissions from soils can be attributed to microbial denitrification and nitrification processes. Bacterial denitrification reactions are catalyzed by the periplasmic (Nap) or membrane-bound (Nar) nitrate reductases, nitrite reductases (NirK/cd 1Nir), nitric oxide reductases (cNor, qNor/ CuANor), and nitrous oxide reductase (Nos) encoded by nap/nar, nir, nor and nos genes, respectively. Rhizobium etli CFN42, the microsymbiont of common bean, is unable to respire nitrate under anoxic conditions and to perform a complete denitrification pathway. This bacterium lacks the nap, nar and nos genes but contains genes encoding NirK and cNor. In this work, we demonstrated that R. etli is able to grow with nitrate as the sole nitrogen source under aerobic and microoxic conditions. Genetic and functional characterization of a gene located in the R. etli chromosome and annotated as narB demonstrated that growth under aerobic or microoxic conditions with nitrate as nitrogen source as well as nitrate reductase activity requires NarB. In addition to be involved in nitrate assimilation, NarB is also required for NO and N2O production by NirK and cNor, respectively, in cells grown microoxically with nitrate as the only N source. Furthermore, β-glucuronidase activity from nirK::uidA and norC::uidA fusions, as well as NorC expression and Nir and Nor activities revealed that expression of nor genes under microoxic conditions also depends on nitrate reduction by NarB. Our results suggest that nitrite produced by NarB from assimilatory nitrate reduction is detoxified by NirK and cNor denitrifying enzymes that convert nitrite into NO which in turn is reduced to N2O, respectively.
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Affiliation(s)
- Alba Hidalgo-García
- Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Granada, Spain
| | - María J Torres
- Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Granada, Spain
| | - Ana Salas
- Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Granada, Spain
| | - Eulogio J Bedmar
- Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Granada, Spain
| | - Lourdes Girard
- Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Mexico
| | - María J Delgado
- Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Granada, Spain
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34
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Abstract
SIGNIFICANCE Iron-sulfur cluster proteins carry out multiple functions, including as regulators of gene transcription/translation in response to environmental stimuli. In all known cases, the cluster acts as the sensory module, where the inherent reactivity/fragility of iron-sulfur clusters with small/redox-active molecules is exploited to effect conformational changes that modulate binding to DNA regulatory sequences. This promotes an often substantial reprogramming of the cellular proteome that enables the organism or cell to adapt to, or counteract, its changing circumstances. Recent Advances: Significant progress has been made recently in the structural and mechanistic characterization of iron-sulfur cluster regulators and, in particular, the O2 and NO sensor FNR, the NO sensor NsrR, and WhiB-like proteins of Actinobacteria. These are the main focus of this review. CRITICAL ISSUES Striking examples of how the local environment controls the cluster sensitivity and reactivity are now emerging, but the basis for this is not yet fully understood for any regulatory family. FUTURE DIRECTIONS Characterization of iron-sulfur cluster regulators has long been hampered by a lack of high-resolution structural data. Although this still presents a major future challenge, recent advances now provide a firm foundation for detailed understanding of how a signal is transduced to effect gene regulation. This requires the identification of often unstable intermediate species, which are difficult to detect and may be hard to distinguish using traditional techniques. Novel approaches will be required to solve these problems.
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Affiliation(s)
- Jason C Crack
- Centre for Molecular and Structural Biochemistry, School of Chemistry, University of East Anglia , Norwich Research Park, Norwich, United Kingdom
| | - Nick E Le Brun
- Centre for Molecular and Structural Biochemistry, School of Chemistry, University of East Anglia , Norwich Research Park, Norwich, United Kingdom
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35
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Mino S, Yoneyama N, Nakagawa S, Takai K, Sawabe T. Enrichment and Genomic Characterization of a N 2O-Reducing Chemolithoautotroph From a Deep-Sea Hydrothermal Vent. Front Bioeng Biotechnol 2018; 6:184. [PMID: 30547029 PMCID: PMC6279868 DOI: 10.3389/fbioe.2018.00184] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2018] [Accepted: 11/13/2018] [Indexed: 01/24/2023] Open
Abstract
Nitrous oxide (N2O) is a greenhouse gas and also leads to stratospheric ozone depletion. In natural environments, only a single N2O sink process is the microbial reduction of N2O to N2, which is mediated by nitrous oxide reductase (NosZ) encoded by nosZ gene. The nosZ phylogeny has two distinct clades, clade I and formerly overlooked clade II. In deep-sea hydrothermal environments, several members of the class Campylobacteria are shown to harbor clade II nosZ gene and perform the complete denitrification of nitrate to N2; however, little is known about their ability to grow on exogenous N2O as the sole electron acceptor. Here, we obtained an enrichment culture from a deep-sea hydrothermal vent in the Southern Mariana Trough, which showed a respiratory N2O reduction with H2 as an electron donor. The single amplicon sequence variant (ASV) presenting 90% similarity to Hydrogenimonas species within the class Campylobacteria was predominant throughout the cultivation period. Metagenomic analyses using a combination of short-read and long-read sequence data succeeded in reconstructing a complete genome of the dominant ASV, which encoded clade II nosZ gene. This study represents the first cultivation analysis that shows the occurrence of N2O-respiring microorganisms in a deep-sea hydrothermal vent and provides the opportunity to assess their capability to reduce N2O emission from the environments.
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Affiliation(s)
- Sayaka Mino
- Laboratory of Microbiology, Faculty of Fisheries Sciences, Hokkaido University, Hakodate, Japan
| | - Naoki Yoneyama
- Laboratory of Microbiology, Faculty of Fisheries Sciences, Hokkaido University, Hakodate, Japan
| | - Satoshi Nakagawa
- Laboratory of Marine Environmental Microbiology, Division of Applied Biosciences, Graduate School of Agriculture, Kyoto University, Kyoto, Japan.,Department of Subsurface Geobiology Analysis and Research (D-SUGAR), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan
| | - Ken Takai
- Department of Subsurface Geobiology Analysis and Research (D-SUGAR), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan
| | - Tomoo Sawabe
- Laboratory of Microbiology, Faculty of Fisheries Sciences, Hokkaido University, Hakodate, Japan
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36
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37
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Sun Y, De Vos P, Willems A. Influence of nitrate and nitrite concentration on N 2 O production via dissimilatory nitrate/nitrite reduction to ammonium in Bacillus paralicheniformis LMG 6934. Microbiologyopen 2018; 7:e00592. [PMID: 29504271 PMCID: PMC6079178 DOI: 10.1002/mbo3.592] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2017] [Revised: 12/17/2017] [Accepted: 12/29/2017] [Indexed: 12/28/2022] Open
Abstract
Until now, the exact mechanisms for N2 O production in dissimilatory nitrate/nitrite reduction to ammonium (DNRA) remain underexplored. Previously, we investigated this mechanism in Bacillus licheniformis and Bacillus paralicheniformis, ubiquitous gram-positive bacteria with many industrial applications, and observed significant strain dependency and media dependency in N2 O production which was thought to correlate with high residual NO2- . Here, we further studied the influence of several physicochemical factors on NO3- (or NO2- ) partitioning and N2 O production in DNRA to shed light on the possible mechanisms of N2 O production. The effects of NO3- concentrations under variable or fixed C/N-NO3- ratios, NO2- concentrations under variable or fixed C/N-NO2- ratios, and NH4+ concentrations under fixed C/N-NO3- ratios were tested during anaerobic incubation of soil bacterium B. paralicheniformis LMG 6934 (previously known as B. licheniformis), a strain with a high nitrite reduction capacity. Monitoring of growth, NO3- , NO2- , NH4+ concentration, and N2 O production in physiological tests revealed that NO3- as well as NO2- concentration showed a linear correlation with N2 O production. Increased NO3- concentration under fixed C/N-NO3- ratios, NO2- concentration, and NH4+ concentration had a significant positive effect on NO3- (or NO2- ) partitioning ([N-NH4+ ]/[N-N2 O]) toward N2 O, which may be a consequence of the (transient) accumulation and subsequent detoxification of NO2- . These findings extend the information on several physiological parameters affecting DNRA and provide a basis for further study on N2 O production during this process.
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Affiliation(s)
- Yihua Sun
- Laboratory of MicrobiologyDepartment of Biochemistry and MicrobiologyGhent UniversityGentBelgium
| | - Paul De Vos
- Laboratory of MicrobiologyDepartment of Biochemistry and MicrobiologyGhent UniversityGentBelgium
| | - Anne Willems
- Laboratory of MicrobiologyDepartment of Biochemistry and MicrobiologyGhent UniversityGentBelgium
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38
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Torres MJ, Avila S, Bedmar EJ, Delgado MJ. Overexpression of the periplasmic nitrate reductase supports anaerobic growth by Ensifer meliloti. FEMS Microbiol Lett 2018; 365:4867969. [DOI: 10.1093/femsle/fny041] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2017] [Accepted: 02/15/2018] [Indexed: 01/10/2023] Open
Affiliation(s)
- María J Torres
- Estación Experimental del Zaidín, CSIC, Profesor Albareda, 1, 18008 Granada, Spain
| | - Sergio Avila
- Estación Experimental del Zaidín, CSIC, Profesor Albareda, 1, 18008 Granada, Spain
| | - Eulogio J Bedmar
- Estación Experimental del Zaidín, CSIC, Profesor Albareda, 1, 18008 Granada, Spain
| | - María J Delgado
- Estación Experimental del Zaidín, CSIC, Profesor Albareda, 1, 18008 Granada, Spain
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39
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Conthe M, Kuenen JG, Kleerebezem R, van Loosdrecht MCM. Exploring microbial N 2 O reduction: a continuous enrichment in nitrogen free medium. ENVIRONMENTAL MICROBIOLOGY REPORTS 2018; 10:102-107. [PMID: 29327471 DOI: 10.1111/1758-2229.12615] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2017] [Accepted: 01/06/2018] [Indexed: 06/07/2023]
Abstract
N2 O is a potent greenhouse gas, but also a potent electron acceptor. In search of thermodynamically favourable - yet undescribed - metabolic pathways involving N2 O reduction, we set up a continuous microbial enrichment, inoculated with activated sludge, fed with N2 O as the sole electron acceptor and acetate as an electron donor. A nitrogen-free mineral medium was used with the intention of creating a selective pressure towards organisms that would use N2 O directly as source of nitrogen for cell synthesis. Instead, we obtained a culture dominated by microorganisms of the Rhodocyclaceae family growing by N2 O reduction to N2 coupled to N2 fixation. Biomass yields of this culture were 40% lower than those of a previously reported culture grown under comparable conditions but with an NH4+-amended medium, as expected from the extra energy expense of N2 fixation. Interestingly, we found no significant difference in yields whether N2 O or acetate was the growth-limiting substrate in the chemostat in contrast to the study with NH4+-amended medium, in which biomass yields were roughly 30% lower during acetate limiting conditions.
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Affiliation(s)
- Monica Conthe
- Department of Biotechnology, Delft University of Technology, Delft, The Netherlands
| | - J Gijs Kuenen
- Department of Biotechnology, Delft University of Technology, Delft, The Netherlands
| | - Robbert Kleerebezem
- Department of Biotechnology, Delft University of Technology, Delft, The Netherlands
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40
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Microbiome analysis and -omics studies of microbial denitrification processes in wastewater treatment: recent advances. SCIENCE CHINA-LIFE SCIENCES 2018; 61:753-761. [DOI: 10.1007/s11427-017-9228-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2017] [Accepted: 11/22/2017] [Indexed: 10/18/2022]
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41
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Abstract
SIGNIFICANCE Iron-sulfur cluster proteins carry out a wide range of functions, including as regulators of gene transcription/translation in response to environmental stimuli. In all known cases, the cluster acts as the sensory module, where the inherent reactivity/fragility of iron-sulfur clusters towards small/redox active molecules is exploited to effect conformational changes that modulate binding to DNA regulatory sequences. This promotes an often substantial re-programming of the cellular proteome that enables the organism or cell to adapt to, or counteract, its changing circumstances. Recent Advances. Significant progress has been made recently in the structural and mechanistic characterization of iron-sulfur cluster regulators and, in particular, the O2 and NO sensor FNR, the NO sensor NsrR, and WhiB-like proteins of Actinobacteria. These are the main focus of this review. CRITICAL ISSUES Striking examples of how the local environment controls the cluster sensitivity and reactivity are now emerging, but the basis for this is not yet fully understood for any regulatory family. FUTURE DIRECTIONS Characterization of iron-sulfur cluster regulators has long been hampered by a lack of high resolution structural data. Though this still presents a major future challenge, recent advances now provide a firm foundation for detailed understanding of how a signal is transduced to effect gene regulation. This requires the identification of often unstable intermediate species, which are difficult to detect and may be hard to distinguish using traditional techniques. Novel approaches will be required to solve these problems.
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Affiliation(s)
- Jason C Crack
- School of Chemistry , University of East Anglia , Norwich, United Kingdom of Great Britain and Northern Ireland , NR4 7TJ ;
| | - Nick E Le Brun
- University of East Anglia, School of Chemistry , University plain , Norwich, United Kingdom of Great Britain and Northern Ireland , NR4 7TJ ;
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42
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Hein S, Witt S, Simon J. Clade II nitrous oxide respiration of Wolinella succinogenes depends on the NosG, -C1, -C2, -H electron transport module, NosB and a Rieske/cytochrome bc complex. Environ Microbiol 2017; 19:4913-4925. [PMID: 28925551 DOI: 10.1111/1462-2920.13935] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2017] [Revised: 09/14/2017] [Accepted: 09/16/2017] [Indexed: 01/20/2023]
Abstract
Microbial reduction of nitrous oxide (N2 O) is an environmentally significant process in the biogeochemical nitrogen cycle. However, it has been recognized only recently that the gene encoding N2 O reductase (nosZ) is organized in varying genetic contexts, thereby defining clade I (or 'typical') and clade II (or 'atypical') N2 O reductases and nos gene clusters. This study addresses the enzymology of the clade II Nos system from Wolinella succinogenes, a nitrate-ammonifying and N2 O-respiring Epsilonproteobacterium that contains a cytochrome c N2 O reductase (cNosZ). The characterization of single non-polar nos gene deletion mutants demonstrated that the NosG, -C1, -C2, -H and -B proteins were essential for N2 O respiration. Moreover, cells of a W. succinogenes mutant lacking a putative menaquinol-oxidizing Rieske/cytochrome bc complex (QcrABC) were found to be incapable of N2 O (and also nitrate) respiration. Proton motive menaquinol oxidation by N2 O is suggested, supported by the finding that the molar yield for W. succinogenes cells grown by N2 O respiration using formate as electron donor exceeded that of fumarate respiration by about 30%. The results demand revision of the electron transport chain model of clade II N2 O respiration and challenge the assumption that NosGH(NapGH)-type iron-sulfur proteins are menaquinol-reactive.
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Affiliation(s)
- Sascha Hein
- Microbial Energy Conversion and Biotechnology, Department of Biology, Technische Universität Darmstadt, Schnittspahnstraße 10, 64287 Darmstadt, Germany
| | - Samantha Witt
- Microbial Energy Conversion and Biotechnology, Department of Biology, Technische Universität Darmstadt, Schnittspahnstraße 10, 64287 Darmstadt, Germany
| | - Jörg Simon
- Microbial Energy Conversion and Biotechnology, Department of Biology, Technische Universität Darmstadt, Schnittspahnstraße 10, 64287 Darmstadt, Germany
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Preimesberger MR, Johnson EA, Nye DB, Lecomte JTJ. Covalent attachment of the heme to Synechococcus hemoglobin alters its reactivity toward nitric oxide. J Inorg Biochem 2017; 177:171-182. [PMID: 28968520 DOI: 10.1016/j.jinorgbio.2017.09.018] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2017] [Revised: 09/18/2017] [Accepted: 09/19/2017] [Indexed: 01/19/2023]
Abstract
The cyanobacterium Synechococcus sp. PCC 7002 produces a monomeric hemoglobin (GlbN) implicated in the detoxification of reactive nitrogen and oxygen species. GlbN contains a b heme, which can be modified under certain reducing conditions. The modified protein (GlbN-A) has one heme-histidine C-N linkage similar to the C-S linkage of cytochrome c. No clear functional role has been assigned to this modification. Here, optical absorbance and NMR spectroscopies were used to compare the reactivity of GlbN and GlbN-A toward nitric oxide (NO). Both forms of the protein are capable of NO dioxygenase activity and both undergo heme bleaching after multiple NO challenges. GlbN and GlbN-A bind NO in the ferric state and form diamagnetic complexes (FeIII-NO) that resist reductive nitrosylation to the paramagnetic FeII-NO forms. Dithionite reduction of FeIII-NO GlbN and GlbN-A, however, resulted in distinct outcomes. Whereas GlbN-A rapidly formed the expected FeII-NO complex, NO binding to FeII GlbN caused immediate heme loss and, remarkably, was followed by slow heme rebinding and HNO (nitrosyl hydride) production. Additionally, combining FeIII GlbN, 15N-labeled nitrite, and excess dithionite resulted in the formation of FeII-H15NO GlbN. Dithionite-mediated HNO production was also observed for the related GlbN from Synechocystis sp. PCC 6803. Although ferrous GlbN-A appeared capable of trapping preformed HNO, the histidine-heme post-translational modification extinguished the NO reduction chemistry associated with GlbN. Overall, the results suggest a role for the covalent modification in FeII GlbNs: protection from NO-mediated heme loss and prevention of HNO formation.
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Affiliation(s)
| | - Eric A Johnson
- T.C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, USA
| | - Dillon B Nye
- T.C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, USA
| | - Juliette T J Lecomte
- T.C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, USA.
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The catalytic cycle of nitrous oxide reductase - The enzyme that catalyzes the last step of denitrification. J Inorg Biochem 2017; 177:423-434. [PMID: 28927704 DOI: 10.1016/j.jinorgbio.2017.09.007] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2017] [Revised: 09/02/2017] [Accepted: 09/08/2017] [Indexed: 01/27/2023]
Abstract
The reduction of the potent greenhouse gas nitrous oxide requires a catalyst to overcome the large activation energy barrier of this reaction. Its biological decomposition to the inert dinitrogen can be accomplished by denitrifiers through nitrous oxide reductase, the enzyme that catalyzes the last step of the denitrification, a pathway of the biogeochemical nitrogen cycle. Nitrous oxide reductase is a multicopper enzyme containing a mixed valence CuA center that can accept electrons from small electron shuttle proteins, triggering electron flow to the catalytic sulfide-bridged tetranuclear copper "CuZ center". This enzyme has been isolated with its catalytic center in two forms, CuZ*(4Cu1S) and CuZ(4Cu2S), proven to be spectroscopic and structurally different. In the last decades, it has been a challenge to characterize the properties of this complex enzyme, due to the different oxidation states observed for each of its centers and the heterogeneity of its preparations. The substrate binding site in those two "CuZ center" forms and which is the active form of the enzyme is still a matter of debate. However, in the last years the application of different spectroscopies, together with theoretical calculations have been useful in answering these questions and in identifying intermediate species of the catalytic cycle. An overview of the spectroscopic, kinetics and structural properties of the two forms of the catalytic "CuZ center" is given here, together with the current knowledge on nitrous oxide reduction mechanism by nitrous oxide reductase and its intermediate species.
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45
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Bueno E, Robles EF, Torres MJ, Krell T, Bedmar EJ, Delgado MJ, Mesa S. Disparate response to microoxia and nitrogen oxides of the Bradyrhizobium japonicum napEDABC, nirK and norCBQD denitrification genes. Nitric Oxide 2017; 68:137-149. [DOI: 10.1016/j.niox.2017.02.002] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2016] [Revised: 01/27/2017] [Accepted: 02/02/2017] [Indexed: 01/25/2023]
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Haase D, Hermann B, Einsle O, Simon J. Epsilonproteobacterial hydroxylamine oxidoreductase (
ε
Hao): characterization of a ‘missing link’ in the multihaem cytochrome
c
family. Mol Microbiol 2017; 105:127-138. [DOI: 10.1111/mmi.13690] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- Doreen Haase
- Microbial Energy Conversion and Biotechnology, Department of BiologyTechnische Universität DarmstadtSchnittspahnstraße 1064287Darmstadt Germany
| | - Bianca Hermann
- Lehrstuhl Biochemie, Institut für BiochemieAlbert‐Ludwigs‐Universität FreiburgAlbertstrasse 2179104Freiburg Germany
| | - Oliver Einsle
- Lehrstuhl Biochemie, Institut für BiochemieAlbert‐Ludwigs‐Universität FreiburgAlbertstrasse 2179104Freiburg Germany
| | - Jörg Simon
- Microbial Energy Conversion and Biotechnology, Department of BiologyTechnische Universität DarmstadtSchnittspahnstraße 1064287Darmstadt Germany
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van den Berg EM, Boleij M, Kuenen JG, Kleerebezem R, van Loosdrecht MCM. DNRA and Denitrification Coexist over a Broad Range of Acetate/N-NO 3- Ratios, in a Chemostat Enrichment Culture. Front Microbiol 2016; 7:1842. [PMID: 27933040 PMCID: PMC5121219 DOI: 10.3389/fmicb.2016.01842] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2016] [Accepted: 11/02/2016] [Indexed: 11/13/2022] Open
Abstract
Denitrification and dissimilatory nitrate reduction to ammonium (DNRA) compete for nitrate in natural and engineered environments. A known important factor in this microbial competition is the ratio of available electron donor and elector acceptor, here expressed as Ac/N ratio (acetate/nitrate-nitrogen). We studied the impact of the Ac/N ratio on the nitrate reduction pathways in chemostat enrichment cultures, grown on acetate mineral medium. Stepwise, conditions were changed from nitrate limitation to nitrate excess in the system by applying a variable Ac/N ratio in the feed. We observed a clear correlation between Ac/N ratio and DNRA activity and the DNRA population in our reactor. The DNRA bacteria dominated under nitrate limiting conditions in the reactor and were outcompeted by denitrifiers under limitation of acetate. Interestingly, in a broad range of Ac/N ratios a dual limitation of acetate and nitrate occurred with co-occurrence of DNRA bacteria and denitrifiers. To explain these observations, the system was described using a kinetic model. The model illustrates that the Ac/N effect and concomitant broad dual limitation range related to the difference in stoichiometry between both processes, as well as the differences in electron donor and acceptor affinities. Population analysis showed that the presumed DRNA-performing bacteria were the same under nitrate limitation and under dual limiting conditions, whereas the presumed denitrifying population changed under single and dual limitation conditions.
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Affiliation(s)
- Eveline M van den Berg
- Environmental Biotechnology Group, Department of Biotechnology, Delft University of Technology Delft, Netherlands
| | - Marissa Boleij
- Environmental Biotechnology Group, Department of Biotechnology, Delft University of Technology Delft, Netherlands
| | - J Gijs Kuenen
- Environmental Biotechnology Group, Department of Biotechnology, Delft University of Technology Delft, Netherlands
| | - Robbert Kleerebezem
- Environmental Biotechnology Group, Department of Biotechnology, Delft University of Technology Delft, Netherlands
| | - Mark C M van Loosdrecht
- Environmental Biotechnology Group, Department of Biotechnology, Delft University of Technology Delft, Netherlands
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