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Sennett LB, Roco CA, Lim NYN, Yavitt JB, Dörsch P, Bakken LR, Shapleigh JP, Frostegård Å. Determining how oxygen legacy affects trajectories of soil denitrifier community dynamics and N 2O emissions. Nat Commun 2024; 15:7298. [PMID: 39181870 PMCID: PMC11344836 DOI: 10.1038/s41467-024-51688-w] [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: 01/12/2024] [Accepted: 08/15/2024] [Indexed: 08/27/2024] Open
Abstract
Denitrification - a key process in the global nitrogen cycle and main source of the greenhouse gas N2O - is intricately controlled by O2. While the transition from aerobic respiration to denitrification is well-studied, our understanding of denitrifier communities' responses to cyclic oxic/anoxic shifts, prevalent in natural and engineered systems, is limited. Here, agricultural soil is exposed to repeated cycles of long or short anoxic spells (LA; SA) or constant oxic conditions (Ox). Surprisingly, denitrification and N2O reduction rates are three times greater in Ox than in LA and SA during a final anoxic incubation, despite comparable bacterial biomass and denitrification gene abundances. Metatranscriptomics indicate that LA favors canonical denitrifiers carrying nosZ clade I. Ox instead favors nosZ clade II-carrying partial- or non-denitrifiers, suggesting efficient partnering of the reduction steps among organisms. SA has the slowest denitrification progression and highest accumulation of intermediates, indicating less functional coordination. The findings demonstrate how adaptations of denitrifier communities to varying O2 conditions are tightly linked to the duration of anoxic episodes, emphasizing the importance of knowing an environment's O2 legacy for accurately predicting N2O emissions originating from denitrification.
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Affiliation(s)
- Louise B Sennett
- Faculty of Chemistry, Biotechnology, and Food Sciences, Norwegian University of Life Sciences, Norwegian University of Life Sciences, Ås, Norway.
| | - Constance A Roco
- Faculty of Chemistry, Biotechnology, and Food Sciences, Norwegian University of Life Sciences, Norwegian University of Life Sciences, Ås, Norway
- Department of Microbiology, Cornell University, Ithaca, NY, USA
| | - Natalie Y N Lim
- Faculty of Chemistry, Biotechnology, and Food Sciences, Norwegian University of Life Sciences, Norwegian University of Life Sciences, Ås, Norway
| | - Joseph B Yavitt
- Department of Natural Resources, Cornell University, Ithaca, NY, USA
| | - Peter Dörsch
- Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, Norwegian University of Life Sciences, Ås, Norway
| | - Lars R Bakken
- Faculty of Chemistry, Biotechnology, and Food Sciences, Norwegian University of Life Sciences, Norwegian University of Life Sciences, Ås, Norway
| | | | - Åsa Frostegård
- Faculty of Chemistry, Biotechnology, and Food Sciences, Norwegian University of Life Sciences, Norwegian University of Life Sciences, Ås, Norway.
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2
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Shaw DR, Terada A, Saikaly PE. Future directions in microbial nitrogen cycling in wastewater treatment. Curr Opin Biotechnol 2024; 88:103163. [PMID: 38897092 DOI: 10.1016/j.copbio.2024.103163] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2024] [Revised: 05/30/2024] [Accepted: 06/03/2024] [Indexed: 06/21/2024]
Abstract
Discoveries in the past decade of novel reactions, processes, and micro-organisms have altered our understanding of microbial nitrogen cycling in wastewater treatment systems. These advancements pave the way for a transition toward more sustainable and energy-efficient wastewater treatment systems that also minimize greenhouse gas emissions. This review highlights these innovative directions in microbial nitrogen cycling within the context of wastewater treatment. Processes such as comammox, Feammox, electro-anammox, and nitrous oxide mitigation offer innovative approaches for sustainable, energy-efficient nitrogen removal. However, while these emerging processes show promise, advancing from laboratory research to practical applications, particularly in decentralized systems, remains a critical next step toward a sustainable and efficient wastewater management.
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Affiliation(s)
- Dario R Shaw
- Water Desalination and Reuse Center (WDRC), King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - Akihiko Terada
- Department of Applied Physics and Chemical Engineering, Department of Industrial Technology and Innovation, Tokyo University of Agriculture and Technology, 2-24-16 Building 4-320 Naka, Koganei, Tokyo 184-8588, Japan.
| | - Pascal E Saikaly
- Water Desalination and Reuse Center (WDRC), King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Kingdom of Saudi Arabia; Environmental Science & Engineering Program, Division of Biological and Environmental Science and Engineering (BESE), King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Kingdom of Saudi Arabia.
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3
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Oba K, Yasuda S, Terada A. Complete genome sequence of Afipia carboxidovorans strain SH125, a non-denitrifying nitrous oxide-reducing bacterium isolated from anammox biomass. Microbiol Resour Announc 2024; 13:e0127923. [PMID: 38385666 DOI: 10.1128/mra.01279-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2024] [Accepted: 02/13/2024] [Indexed: 02/23/2024] Open
Abstract
Here, we report a genome sequence of Afipia carboxidovorans strain SH125 isolated from an anammox reactor. This facultative anaerobic strain possesses the clade I-type nitrous oxide (N2O) reductase gene, devoid of nitrite- and nitric oxide reductase genes. Deciphering the genome will help explore N2O reducers instrumental in N2O mitigation.
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Affiliation(s)
- Kohei Oba
- Department of Applied Physics and Chemical Engineering, Tokyo University of Agriculture and Technology, Koganei, Tokyo, Japan
| | - Shohei Yasuda
- Civil Engineering, School of Engineering, College of Science and Engineering, University of Galway, Galway, Ireland
| | - Akihiko Terada
- Department of Applied Physics and Chemical Engineering, Tokyo University of Agriculture and Technology, Koganei, Tokyo, Japan
- Global Innovation Research Institute, Tokyo University of Agriculture and Technology, Fuchu, Tokyo, Japan
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4
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Wasai-Hara S, Itakura M, Fernandes Siqueira A, Takemoto D, Sugawara M, Mitsui H, Sato S, Inagaki N, Yamazaki T, Imaizumi-Anraku H, Shimoda Y, Minamisawa K. Bradyrhizobium ottawaense efficiently reduces nitrous oxide through high nosZ gene expression. Sci Rep 2023; 13:18862. [PMID: 37914789 PMCID: PMC10620151 DOI: 10.1038/s41598-023-46019-w] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2023] [Accepted: 10/26/2023] [Indexed: 11/03/2023] Open
Abstract
N2O is an important greenhouse gas influencing global warming, and agricultural land is the predominant (anthropogenic) source of N2O emissions. Here, we report the high N2O-reducing activity of Bradyrhizobium ottawaense, suggesting the potential for efficiently mitigating N2O emission from agricultural lands. Among the 15 B. ottawaense isolates examined, the N2O-reducing activities of most (13) strains were approximately five-fold higher than that of Bradyrhizobium diazoefficiens USDA110T under anaerobic conditions. This robust N2O-reducing activity of B. ottawaense was confirmed by N2O reductase (NosZ) protein levels and by mitigation of N2O emitted by nodule decomposition in laboratory system. While the NosZ of B. ottawaense and B. diazoefficiens showed high homology, nosZ gene expression in B. ottawaense was over 150-fold higher than that in B. diazoefficiens USDA110T, suggesting the high N2O-reducing activity of B. ottawaense is achieved by high nos expression. Furthermore, we examined the nos operon transcription start sites and found that, unlike B. diazoefficiens, B. ottawaense has two transcription start sites under N2O-respiring conditions, which may contribute to the high nosZ expression. Our study indicates the potential of B. ottawaense for effective N2O reduction and unique regulation of nos gene expression towards the high performance of N2O mitigation in the soil.
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Affiliation(s)
- Sawa Wasai-Hara
- Institute of Agrobiological Sciences, National Agriculture and Food Research Organization (NARO), Tsukuba, Ibaraki, Japan
- Graduate School of Life Sciences, Tohoku University, Sendai, Miyagi, Japan
| | - Manabu Itakura
- Graduate School of Life Sciences, Tohoku University, Sendai, Miyagi, Japan
| | | | - Daisaku Takemoto
- Research Center for Advanced Analysis, National Agriculture and Food Research Organization (NARO), Tsukuba, Ibaraki, Japan
| | - Masayuki Sugawara
- Graduate School of Life Sciences, Tohoku University, Sendai, Miyagi, Japan
| | - Hisayuki Mitsui
- Graduate School of Life Sciences, Tohoku University, Sendai, Miyagi, Japan
| | - Shusei Sato
- Graduate School of Life Sciences, Tohoku University, Sendai, Miyagi, Japan
| | - Noritoshi Inagaki
- Research Center for Advanced Analysis, National Agriculture and Food Research Organization (NARO), Tsukuba, Ibaraki, Japan
| | - Toshimasa Yamazaki
- Research Center for Advanced Analysis, National Agriculture and Food Research Organization (NARO), Tsukuba, Ibaraki, Japan
| | - Haruko Imaizumi-Anraku
- Institute of Agrobiological Sciences, National Agriculture and Food Research Organization (NARO), Tsukuba, Ibaraki, Japan
| | - Yoshikazu Shimoda
- Institute of Agrobiological Sciences, National Agriculture and Food Research Organization (NARO), Tsukuba, Ibaraki, Japan.
| | - Kiwamu Minamisawa
- Graduate School of Life Sciences, Tohoku University, Sendai, Miyagi, Japan.
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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: 2] [Impact Index Per Article: 2.0] [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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Read-Daily B, Ben Maamar S, Sabba F, Green S, Nerenberg R. Effect of nitrous oxide (N 2O) on the structure and function of nitrogen-oxide reducing microbial communities. CHEMOSPHERE 2022; 307:135819. [PMID: 35977570 DOI: 10.1016/j.chemosphere.2022.135819] [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: 05/13/2022] [Revised: 07/18/2022] [Accepted: 07/20/2022] [Indexed: 06/15/2023]
Abstract
Nitrous oxide (N2O) is a potent greenhouse gas that can be produced by nitrifying and denitrifying bacteria. Yet the effects of N2O on microbial communities is not well understood. We used batch tests to explore the effects of N2O on mixed denitrifying communities. Batch tests were carried out with acetate as the electron donor and with the following electron acceptors: nitrate (NO3-), nitrite (NO2-), N2O, NO3- + N2O, and NO2- + N2O. Activated sludge from a municipal wastewater treatment plant was used as the inoculum. The bacteria grew readily with N2O as the sole acceptor. When N2O was provided along with NO3- or NO2-, it was used concurrently and resulted in higher growth rates than the same acceptors without added N2O. The microbial communities resulting from N2O addition were significantly different at the genus level from those with just NO3- or NO2-. Tests with N2O as the sole added acceptor revealed a reduced diversity. Analysis of inferred gene content using PICRUSt2 indicated a greater abundance of genera with a complete denitrification pathway when growing on N2O or NO2-, relative to all other tests. This suggests that specific N2O reduction rates are high, and that N2O alone selects for a low-diversity, fully denitrifying community. When N2O is present with NO2- or NO3-, the microbial communities were more diverse and did not select exclusively for full denitrifiers. N2O alone appears to select for a "generalist" community with full denitrification pathways and lower diversity. In terms of denitrification genes, the combination of acceptors with N2O appeared to increase the number of microbes carrying nirK, while fully denitrifying bacteria appear more likely to carry nirS. Lastly, all the taxa in NO2- and N2O samples were predicted to harbor nosZ. This suggests the potential for reduced N2O emissions in denitrifying systems.
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Affiliation(s)
- B Read-Daily
- Department of Engineering and Physics, Elizabethtown College, Elizabethtown, PA, 17022, USA; Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, Notre Dame, IN, 46556, USA
| | - S Ben Maamar
- Samuel J. Wood Library, Weill Cornell Medicine, New York, NY, 10065, USA
| | - F Sabba
- Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, Notre Dame, IN, 46556, USA; Black & Veatch, KS, USA
| | - S Green
- Rush Medical College, Chicago, IL, 60612, USA
| | - R Nerenberg
- Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, Notre Dame, IN, 46556, USA.
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7
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Klimasmith IM, Kent AD. Micromanaging the nitrogen cycle in agroecosystems. Trends Microbiol 2022; 30:1045-1055. [PMID: 35618540 DOI: 10.1016/j.tim.2022.04.006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2021] [Revised: 03/29/2022] [Accepted: 04/29/2022] [Indexed: 01/13/2023]
Abstract
While large inputs of synthetic nitrogen fertilizers enable our current rate of crop production and feed a growing global population, these fertilizers come at a heavy environmental cost. Driven by microbial processes, excess applied nitrogen is lost from agroecosystems as nitrate and nitrous oxide (N2O) contaminating aquatic ecosystems and contributing to climate change. Interest in nitrogen-fixing microorganisms as an alternative to synthetic fertilizers is rapidly accelerating. Microbial inoculants offer the promise of a sustainable and affordable source of nitrogen, but the impact of inoculants on nitrogen dynamics at an ecosystem level is not fully understood. This review synthesizes recent studies on microbial inoculants as tools for nutrient management and considers the ramifications of inoculants for nitrogen transformations beyond fixation.
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Affiliation(s)
- Isaac M Klimasmith
- Natural Resources and Environmental Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Angela D Kent
- Natural Resources and Environmental Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
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8
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Oba K, Suenaga T, Kuroiwa M, Riya S, Terada A. Exploring the Functions of Efficient Canonical Denitrifying Bacteria as N 2O Sinks: Implications from 15N Tracer and Transcriptome Analyses. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2022; 56:11694-11706. [PMID: 35917165 DOI: 10.1021/acs.est.2c02119] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
In denitrifying reactors, canonical complete denitrifying bacteria reduce nitrate (NO3-) to nitrogen via N2O. However, they can also produce N2O under certain conditions. We used a 15N tracer method, in which 15N-labeled NO3-/nitrite (NO2-) and nonlabeled N2O were simultaneously supplied with organic electron donors to five canonical complete denitrifying bacteria affiliated with either Clade I or Clade II nosZ. We calculated their NO3-, NO2-, and N2O consumption rates. The Clade II nosZ bacterium Azospira sp. strain I13 had the highest N2O consumption rate (3.47 ± 0.07 fmol/cell/h) and the second lowest NO3- consumption rate (0.20 ± 0.03 fmol/cell/h); hence, it is a N2O sink. A change from peptone- to acetate/citrate-based organic electron donors increased the NO3- consumption rate by 4.8 fold but barely affected the N2O consumption rate. Electron flow was directed to N2O rather than NO3- in Azospira sp. strain I13 and Az. oryzae strain PS only exerting a N2O sink but to NO3- in the Clade I nosZ N2O-reducing bacteria Pseudomonas stutzeri strain JCM 5965 and Alicycliphilus denitrificans strain I51. Transcriptome analyses revealed that the genotype could not fully describe the phenotype. The results show that N2O production and consumption differ among canonical denitrifying bacteria and will be useful for developing N2O mitigation strategies.
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Affiliation(s)
- Kohei Oba
- Department of Chemical Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Naka-Cho, Koganei, Tokyo 184-8588, Japan
| | - Toshikazu Suenaga
- Global Innovation Research Institute, Tokyo University of Agriculture and Technology, 3-8-1 Harumi-Cho, Fuchu, Tokyo 185-8538, Japan
- Department of Chemical Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashi-hiroshima, Hiroshima 739-8527, Japan
| | - Megumi Kuroiwa
- Department of Chemical Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Naka-Cho, Koganei, Tokyo 184-8588, Japan
| | - Shohei Riya
- Department of Chemical Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Naka-Cho, Koganei, Tokyo 184-8588, Japan
- Global Innovation Research Institute, Tokyo University of Agriculture and Technology, 3-8-1 Harumi-Cho, Fuchu, Tokyo 185-8538, Japan
| | - Akihiko Terada
- Department of Chemical Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Naka-Cho, Koganei, Tokyo 184-8588, Japan
- Global Innovation Research Institute, Tokyo University of Agriculture and Technology, 3-8-1 Harumi-Cho, Fuchu, Tokyo 185-8538, Japan
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A Dual Enrichment Strategy Provides Soil- and Digestate-Competent Nitrous Oxide-Respiring Bacteria for Mitigating Climate Forcing in Agriculture. mBio 2022; 13:e0078822. [PMID: 35638872 PMCID: PMC9239227 DOI: 10.1128/mbio.00788-22] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Manipulating soil metabolism through heavy inoculation with microbes is feasible if organic wastes can be utilized as the substrate for growth and vector as a fertilizer. This, however, requires organisms active in both digestate and soil (generalists). Here, we present a dual enrichment strategy to enrich and isolate such generalists among N2O-respiring bacteria (NRB) in soil and digestates, to be used as an inoculum for strengthening the N2O-reduction capacity of soils. The enrichment strategy utilizes sequential batch enrichment cultures alternating between sterilized digestate and soil as substrates, with each batch initiated with limited O2 and unlimited N2O. The cultures were monitored for gas kinetics and community composition. As predicted by a Lotka-Volterra competition model, cluster analysis identified generalist operational taxonomic units (OTUs) which became dominant, digestate/soil-specialists which did not, and a majority that were gradually diluted out. We isolated several NRBs circumscribed by generalist OTUs. Their denitrification genes and phenotypes predicted a variable capacity to act as N2O-sinks, while all genomes predicted broad catabolic capacity. The latter contrasts with previous attempts to enrich NRB by anaerobic incubation of unsterilized digestate only, which selected for organisms with a catabolic capacity limited to fermentation products. The two isolates with the most promising characteristics as N2O sinks were aPseudomonas sp. with a full-fledged denitrification-pathway and a Cloacibacterium sp. carrying only N2O reductase (clade II), and soil experiments confirmed their capacity to reduce N2O-emissions from soil. The successful enrichment of NRB with broad catabolic spectra suggests that the concept of dual enrichment should also be applicable for enrichment of generalists with traits other than N2O reduction.
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Duffner C, Kublik S, Fösel B, Frostegård Å, Schloter M, Bakken L, Schulz S. Genotypic and phenotypic characterization of hydrogenotrophic denitrifiers. Environ Microbiol 2022; 24:1887-1901. [PMID: 35106904 DOI: 10.1111/1462-2920.15921] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2021] [Revised: 01/20/2022] [Accepted: 01/20/2022] [Indexed: 11/30/2022]
Abstract
Stimulating litho-autotrophic denitrification in aquifers with hydrogen is a promising strategy to remove excess NO3 - , but it often entails accumulation of the cytotoxic intermediate NO2 - and the greenhouse gas N2 O. To explore if these high NO2 - and N2 O concentrations are caused by differences in the genomic composition, the regulation of gene transcription or the kinetics of the reductases involved, we isolated hydrogenotrophic denitrifiers from a polluted aquifer, performed whole-genome sequencing and investigated their phenotypes. We therefore assessed the kinetics of NO2 - , NO, N2 O, N2 and O2 as they depleted O2 and transitioned to denitrification with NO3 - as the only electron acceptor and hydrogen as the electron donor. Isolates with a complete denitrification pathway, although differing intermediate accumulation, were closely related to Dechloromonas denitrificans, Ferribacterium limneticum or Hydrogenophaga taeniospiralis. High NO2 - accumulation was associated with the reductases' kinetics. While available, electrons only flowed towards NO3 - in the narG-containing H. taeniospiralis but flowed concurrently to all denitrification intermediates in the napA-containing D. denitrificans and F. limneticum. The denitrification regulator RegAB, present in the napA strains, may further secure low intermediate accumulation. High N2 O accumulation only occurred during the transition to denitrification and is thus likely caused by delayed N2 O reductase expression.
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Affiliation(s)
- Clara Duffner
- Chair of Soil Science, TUM School of Life Sciences Weihenstephan, Technical University of Munich, Freising, Germany.,Research Unit Comparative Microbiome Analysis, Helmholtz Zentrum München, Neuherberg, Germany
| | - Susanne Kublik
- Research Unit Comparative Microbiome Analysis, Helmholtz Zentrum München, Neuherberg, Germany
| | - Bärbel Fösel
- Research Unit Comparative Microbiome Analysis, Helmholtz Zentrum München, Neuherberg, Germany
| | - Åsa Frostegård
- Department of Chemistry, Biotechnology and Food Sciences, Norwegian University of Life Sciences, Ås, Norway
| | - Michael Schloter
- Chair of Soil Science, TUM School of Life Sciences Weihenstephan, Technical University of Munich, Freising, Germany.,Research Unit Comparative Microbiome Analysis, Helmholtz Zentrum München, Neuherberg, Germany
| | - Lars Bakken
- Department of Chemistry, Biotechnology and Food Sciences, Norwegian University of Life Sciences, Ås, Norway
| | - Stefanie Schulz
- Research Unit Comparative Microbiome Analysis, Helmholtz Zentrum München, Neuherberg, Germany
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11
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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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12
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Frostegård Å, Vick SHW, Lim NYN, Bakken LR, Shapleigh JP. Linking meta-omics to the kinetics of denitrification intermediates reveals pH-dependent causes of N 2O emissions and nitrite accumulation in soil. THE ISME JOURNAL 2022; 16:26-37. [PMID: 34211102 PMCID: PMC8692524 DOI: 10.1038/s41396-021-01045-2] [Citation(s) in RCA: 28] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/15/2021] [Revised: 06/07/2021] [Accepted: 06/16/2021] [Indexed: 11/24/2022]
Abstract
Soil pH is a key controller of denitrification. We analysed the metagenomics/transcriptomics and phenomics of two soils from a long-term liming experiment, SoilN (pH 6.8) and un-limed SoilA (pH 3.8). SoilA had severely delayed N2O reduction despite early transcription of nosZ (mainly clade I), encoding N2O reductase, by diverse denitrifiers. This shows that post-transcriptionally hampered maturation of the NosZ apo-protein at low pH is a generic phenomenon. Identification of transcript reads of several accessory genes in the nos cluster indicated that enzymes for NosZ maturation were present across a range of organisms, eliminating their absence as an explanation for the failure to produce a functional enzyme. nir transcript abundances (for NO2- reductase) in SoilA suggest that low NO2- concentrations in acidic soils, often ascribed to abiotic degradation, are primarily due to biological activity. The accumulation of NO2- in neutral soil was ascribed to high nar expression (nitrate reductase). The -omics results revealed dominance of nirK over nirS in both soils while qPCR showed the opposite, demonstrating that standard primer pairs only capture a fraction of the nirK pool. qnor encoding NO reductase was strongly expressed in SoilA, implying an important role in controlling NO. Production of HONO, for which some studies claim higher, others lower, emissions from NO2- accumulating soil, was estimated to be ten times higher from SoilA than from SoilN. The study extends our understanding of denitrification-driven gas emissions and the diversity of bacteria involved and demonstrates that gene and transcript quantifications cannot always reliably predict community phenotypes.
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Affiliation(s)
- Åsa Frostegård
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, Ås, Norway.
| | - Silas H W Vick
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, Ås, Norway
| | - Natalie Y N Lim
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, Ås, Norway
| | - Lars R Bakken
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, Ås, Norway
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13
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Zhao R, Li X, Bei S, Li D, Li H, Christie P, Bender SF, Zhang J. Enrichment of nosZ-type denitrifiers by arbuscular mycorrhizal fungi mitigates N 2 O emissions from soybean stubbles. Environ Microbiol 2021; 23:6587-6602. [PMID: 34672071 DOI: 10.1111/1462-2920.15815] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2021] [Accepted: 10/05/2021] [Indexed: 11/27/2022]
Abstract
Hotspots of N2 O emissions are generated from legume residues during decomposition. Arbuscular mycorrhizal fungi (AMF) from co-cultivated intercropped plants may proliferate into the microsites and interact with soil microbes to reduce N2 O emissions. Yet, the mechanisms by which or how mycorrhizal hyphae affect nitrifiers and denitrifiers in the legume residues remain ambiguous. Here, a split-microcosm experiment was conducted to assess hyphae of Rhizophagus aggregatus from neighbouring maize on overall N2 O emissions from stubbles of nodulated or non-nodulated soybean. Soil microbes from fields intercropped with maize/soybean amended with fertilizer nitrogen (SS-N1) or unamended (SS-N0) were added to the soybean chamber only. AMF hyphae consistently reduced N2 O emissions by 20.8%-61.5%. Generally, AMF hyphae promoted the abundance of N2 O-consuming (nosZ-type) denitrifiers and altered their community composition. The effects were partly associated with increasing MBC and DOC. By contrast, AMF reduced the abundance of nirK-type denitrifiers in the nodulated SS-N0 treatment only and that of AOB in the non-nodulated SS-N1 treatment. Taken together, our results show that AMF reduced N2 O emissions from soybean stubbles, mainly through the promotion of N2 O-consuming denitrifiers. This holds promise for mitigating N2 O emissions by manipulating the efficacious AMF and their associated microbes in cereal/legume intercropping systems.
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Affiliation(s)
- Ruotong Zhao
- College of Resources and Environmental Sciences, National Academy of Agriculture Green Development, Key Laboratory of Plant-Soil Interactions, Ministry of Education, China Agricultural University, Beijing, 100193, China
| | - Xia Li
- College of Resources and Environmental Sciences, National Academy of Agriculture Green Development, Key Laboratory of Plant-Soil Interactions, Ministry of Education, China Agricultural University, Beijing, 100193, China
- School of Life Science, Shanxi Datong University, Datong, 037009, China
| | - Shuikuan Bei
- College of Resources and Environmental Sciences, National Academy of Agriculture Green Development, Key Laboratory of Plant-Soil Interactions, Ministry of Education, China Agricultural University, Beijing, 100193, China
| | - Dandan Li
- College of Resources and Environmental Sciences, National Academy of Agriculture Green Development, Key Laboratory of Plant-Soil Interactions, Ministry of Education, China Agricultural University, Beijing, 100193, China
| | - Haigang Li
- Inner Mongolia Key Laboratory of Soil Quality and Nutrient Resources, Key Laboratory of Grassland Resource (IMAU), Ministry of Education, College of Grassland, Resources and Environment, Inner Mongolia Agricultural University, Hohhot, 010018, China
| | - Peter Christie
- College of Resources and Environmental Sciences, National Academy of Agriculture Green Development, Key Laboratory of Plant-Soil Interactions, Ministry of Education, China Agricultural University, Beijing, 100193, China
| | - S Franz Bender
- Plant Soil Interactions, Division Agroecology and Environment, Agroscope, Reckenholzstrasse 191, Zurich, CH-8046, Switzerland
| | - Junling Zhang
- College of Resources and Environmental Sciences, National Academy of Agriculture Green Development, Key Laboratory of Plant-Soil Interactions, Ministry of Education, China Agricultural University, Beijing, 100193, China
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14
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Jonassen KR, Hagen LH, Vick SHW, Arntzen MØ, Eijsink VGH, Frostegård Å, Lycus P, Molstad L, Pope PB, Bakken LR. Nitrous oxide respiring bacteria in biogas digestates for reduced agricultural emissions. ISME JOURNAL 2021; 16:580-590. [PMID: 34489539 PMCID: PMC8776835 DOI: 10.1038/s41396-021-01101-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/20/2021] [Revised: 08/10/2021] [Accepted: 08/19/2021] [Indexed: 11/17/2022]
Abstract
Inoculating agricultural soils with nitrous oxide respiring bacteria (NRB) can reduce N2O-emission, but would be impractical as a standalone operation. Here we demonstrate that digestates obtained after biogas production are suitable substrates and vectors for NRB. We show that indigenous NRB in digestates grew to high abundance during anaerobic enrichment under N2O. Gas-kinetics and meta-omic analyses showed that these NRB’s, recovered as metagenome-assembled genomes (MAGs), grew by harvesting fermentation intermediates of the methanogenic consortium. Three NRB’s were isolated, one of which matched the recovered MAG of a Dechloromonas, deemed by proteomics to be the dominant producer of N2O-reductase in the enrichment. While the isolates harbored genes required for a full denitrification pathway and could thus both produce and sequester N2O, their regulatory traits predicted that they act as N2O sinks in soil, which was confirmed experimentally. The isolates were grown by aerobic respiration in digestates, and fertilization with these NRB-enriched digestates reduced N2O emissions from soil. Our use of digestates for low-cost and large-scale inoculation with NRB in soil can be taken as a blueprint for future applications of this powerful instrument to engineer the soil microbiome, be it for enhancing plant growth, bioremediation, or any other desirable function.
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Affiliation(s)
- Kjell Rune Jonassen
- Faculty of Chemistry, Biotechnology and Food Science, NMBU - Norwegian University of Life Sciences, Ås, Norway.,VEAS WWTP, Slemmestad, Norway
| | - Live H Hagen
- Faculty of Chemistry, Biotechnology and Food Science, NMBU - Norwegian University of Life Sciences, Ås, Norway
| | - Silas H W Vick
- Faculty of Chemistry, Biotechnology and Food Science, NMBU - Norwegian University of Life Sciences, Ås, Norway
| | - Magnus Ø Arntzen
- Faculty of Chemistry, Biotechnology and Food Science, NMBU - Norwegian University of Life Sciences, Ås, Norway
| | - Vincent G H Eijsink
- Faculty of Chemistry, Biotechnology and Food Science, NMBU - Norwegian University of Life Sciences, Ås, Norway
| | - Åsa Frostegård
- Faculty of Chemistry, Biotechnology and Food Science, NMBU - Norwegian University of Life Sciences, Ås, Norway
| | - Pawel Lycus
- Faculty of Chemistry, Biotechnology and Food Science, NMBU - Norwegian University of Life Sciences, Ås, Norway
| | - Lars Molstad
- Faculty of Science and Technology, Norwegian University of Life Sciences, Ås, Norway
| | - Phillip B Pope
- Faculty of Chemistry, Biotechnology and Food Science, NMBU - Norwegian University of Life Sciences, Ås, Norway.,Faculty of Biosciences, NMBU - Norwegian University of Life Sciences, Ås, Norway
| | - Lars R Bakken
- Faculty of Chemistry, Biotechnology and Food Science, NMBU - Norwegian University of Life Sciences, Ås, Norway.
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15
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Semedo M, Wittorf L, Hallin S, Song B. Differential expression of clade I and II N2O reductase genes in denitrifying Thauera linaloolentis 47LolT under different nitrogen conditions. FEMS Microbiol Lett 2021; 367:6029120. [PMID: 33296469 DOI: 10.1093/femsle/fnaa205] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2020] [Accepted: 12/07/2020] [Indexed: 01/14/2023] Open
Abstract
Nitrous oxide (N2O) is a potent greenhouse gas and its reduction to dinitrogen gas by the N2O reductase (encoded by the nosZ gene) is the only known biological N2O sink. Within the nosZ phylogeny there are two major clades (I and II), which seem to have different ecological niches. However, physiological differences of nosZI and nosZII expression that may impact emissions of N2O are not well understood. Here, we evaluated the differential expression of nosZI and nosZII, both present in Thauera linaloolentis strain 47LolT, in response to N2O concentration and the presence of the competing electron acceptor nitrate (NO3-). Different N2O levels had a negligible effect on the expression of both nosZ clades. Interestingly, nosZII expression was strongly upregulated in the absence of NO3-, while nosZI expression remained constant across the conditions tested. Thus, NO3- possibly inhibited nosZII expression, which suggests that N2O mitigation mediated by nosZII can be restricted due to the presence of NO3- in the environment. This is the first study demonstrating differential expression of nosZI and nosZII genes under the same physiological conditions and their implications for N2O emission under varying environmental conditions in terms of NO3- availability.
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Affiliation(s)
- Miguel Semedo
- Department of Biological Sciences, Virginia Institute of Marine Science, College of William & Mary, P.O. Box 1346, Gloucester Point, Virginia 23062, USA
| | - Lea Wittorf
- Department of Forest Mycology and Plant Pathology, Swedish University of Agricultural Sciences, Box 7025, 750 07 Uppsala, Sweden, Sweden
| | - Sara Hallin
- Department of Forest Mycology and Plant Pathology, Swedish University of Agricultural Sciences, Box 7025, 750 07 Uppsala, Sweden, Sweden
| | - Bongkeun Song
- Department of Biological Sciences, Virginia Institute of Marine Science, College of William & Mary, P.O. Box 1346, Gloucester Point, Virginia 23062, USA
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16
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Duffner C, Wunderlich A, Schloter M, Schulz S, Einsiedl F. Strategies to Overcome Intermediate Accumulation During in situ Nitrate Remediation in Groundwater by Hydrogenotrophic Denitrification. Front Microbiol 2021; 12:610437. [PMID: 33763037 PMCID: PMC7982820 DOI: 10.3389/fmicb.2021.610437] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2020] [Accepted: 02/15/2021] [Indexed: 11/13/2022] Open
Abstract
Bioremediation of polluted groundwater is one of the most difficult actions in environmental science. Nonetheless, the clean-up of nitrate polluted groundwater may become increasingly important as nitrate concentrations frequently exceed the EU drinking water limit of 50 mg L-1, largely due to intensification of agriculture and food production. Denitrifiers are natural catalysts that can reduce increasing nitrogen loading of aquatic ecosystems. Porous aquifers with high nitrate loading are largely electron donor limited and additionally, high dissolved oxygen concentrations are known to reduce the efficiency of denitrification. Therefore, denitrification lag times (time prior to commencement of microbial nitrate reduction) up to decades were determined for such groundwater systems. The stimulation of autotrophic denitrifiers by the injection of hydrogen into nitrate polluted regional groundwater systems may represent a promising remediation strategy for such environments. However, besides high costs other drawbacks, such as the transient or lasting accumulation of the cytotoxic intermediate nitrite or the formation of the potent greenhouse gas nitrous oxide, have been described. In this article, we detect causes of incomplete denitrification, which include environmental factors and physiological characteristics of the underlying bacteria and provide possible mitigation approaches.
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Affiliation(s)
- Clara Duffner
- Chair of Soil Science, TUM School of Life Sciences Weihenstephan, Technical University of Munich, Freising, Germany
- Research Unit Comparative Microbiome Analysis, Helmholtz Center Munich, Neuherberg, Germany
| | - Anja Wunderlich
- Chair of Hydrogeology, TUM Department of Civil, Geo and Environmental Engineering, Technical University of Munich, Munich, Germany
| | - Michael Schloter
- Chair of Soil Science, TUM School of Life Sciences Weihenstephan, Technical University of Munich, Freising, Germany
- Research Unit Comparative Microbiome Analysis, Helmholtz Center Munich, Neuherberg, Germany
| | - Stefanie Schulz
- Research Unit Comparative Microbiome Analysis, Helmholtz Center Munich, Neuherberg, Germany
| | - Florian Einsiedl
- Chair of Hydrogeology, TUM Department of Civil, Geo and Environmental Engineering, Technical University of Munich, Munich, Germany
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17
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Rhizobia: highways to NO. Biochem Soc Trans 2021; 49:495-505. [PMID: 33544133 DOI: 10.1042/bst20200989] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2020] [Revised: 01/06/2021] [Accepted: 01/07/2021] [Indexed: 02/02/2023]
Abstract
The interaction between rhizobia and their legume host plants conduces to the formation of specialized root organs called nodules where rhizobia differentiate into bacteroids which fix atmospheric nitrogen to the benefit of the plant. This beneficial symbiosis is of importance in the context of sustainable agriculture as legumes do not require the addition of nitrogen fertilizer to grow. Interestingly, nitric oxide (NO) has been detected at various steps of the rhizobium-legume symbiosis where it has been shown to play multifaceted roles. Both bacterial and plant partners are involved in NO synthesis in nodules. To better understand the role of NO, and in particular the role of bacterial NO, at all steps of rhizobia-legumes interaction, the enzymatic sources of NO have to be elucidated. In this review, we discuss different enzymatic reactions by which rhizobia may potentially produce NO. We argue that there is most probably no NO synthase activity in rhizobia, and that instead the NO2- reductase nirK, which is part of the denitrification pathway, is the main bacterial source of NO. The nitrate assimilation pathway might contribute to NO production but only when denitrification is active. The different approaches to measure NO in rhizobia are also addressed.
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18
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Gao Y, Mania D, Mousavi SA, Lycus P, Arntzen MØ, Woliy K, Lindström K, Shapleigh JP, Bakken LR, Frostegård Å. Competition for electrons favours N 2 O reduction in denitrifying Bradyrhizobium isolates. Environ Microbiol 2021; 23:2244-2259. [PMID: 33463871 DOI: 10.1111/1462-2920.15404] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2020] [Revised: 12/21/2020] [Accepted: 01/15/2021] [Indexed: 11/28/2022]
Abstract
Bradyrhizobia are common members of soil microbiomes and known as N2 -fixing symbionts of economically important legumes. Many are also denitrifiers, which can act as sinks or sources for N2 O. Inoculation with compatible rhizobia is often needed for optimal N2 -fixation, but the choice of inoculant may have consequences for N2 O emission. Here, we determined the phylogeny and denitrification capacity of Bradyrhizobium strains, most of them isolated from peanut-nodules. Analyses of genomes and denitrification end-points showed that all were denitrifiers, but only ~1/3 could reduce N2 O. The N2 O-reducing isolates had strong preference for N2 O- over NO3 - -reduction. Such preference was also observed in a study of other bradyrhizobia and tentatively ascribed to competition between the electron pathways to Nap (periplasmic NO3 - reductase) and Nos (N2 O reductase). Another possible explanation is lower abundance of Nap than Nos. Here, proteomics revealed that Nap was instead more abundant than Nos, supporting the hypothesis that the electron pathway to Nos outcompetes that to Nap. In contrast, Paracoccus denitrificans, which has membrane-bond NO3 - reductase (Nar), reduced N2 O and NO3 - simultaneously. We propose that the control at the metabolic level, favouring N2 O reduction over NO3 - reduction, applies also to other denitrifiers carrying Nos and Nap but lacking Nar.
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Affiliation(s)
- Yuan Gao
- Faculty of Chemistry, Biotechnology and Food Sciences, Norwegian University of Life Sciences, Aas, Norway
| | - Daniel Mania
- Faculty of Chemistry, Biotechnology and Food Sciences, Norwegian University of Life Sciences, Aas, Norway
| | - Seyed Abdollah Mousavi
- Ecosystems and Environment Research programme, Faculty of Biological and Environmental Sciences, and Helsinki Institute of Sustainability Science (HELSUS), University of Helsinki, Finland
| | - Pawel Lycus
- Faculty of Chemistry, Biotechnology and Food Sciences, Norwegian University of Life Sciences, Aas, Norway
| | - Magnus Ø Arntzen
- Faculty of Chemistry, Biotechnology and Food Sciences, Norwegian University of Life Sciences, Aas, Norway
| | - Kedir Woliy
- Faculty of Chemistry, Biotechnology and Food Sciences, Norwegian University of Life Sciences, Aas, Norway
| | - Kristina Lindström
- Ecosystems and Environment Research programme, Faculty of Biological and Environmental Sciences, and Helsinki Institute of Sustainability Science (HELSUS), University of Helsinki, Finland
| | | | - Lars R Bakken
- Faculty of Chemistry, Biotechnology and Food Sciences, Norwegian University of Life Sciences, Aas, Norway
| | - Åsa Frostegård
- Faculty of Chemistry, Biotechnology and Food Sciences, Norwegian University of Life Sciences, Aas, Norway
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19
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Voegel TM, Larrabee MM, Nelson LM. Development of droplet digital PCR assays to quantify genes involved in nitrification and denitrification, comparison with quantitative real-time PCR and validation of assays in vineyard soil. Can J Microbiol 2020; 67:174-187. [PMID: 32910858 DOI: 10.1139/cjm-2020-0033] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Quantifying genes in soil is important to relate the abundance of soil bacteria to biogeochemical cycles. Quantitative real-time PCR is widely used for quantification, but its use with environmental samples is limited by poor reaction efficiencies or by PCR inhibition through co-purified soil substances. Droplet digital PCR (ddPCR) is a technology for absolute, sensitive quantification of genes. This study optimized eight ddPCR assays to quantify total bacteria and archaea as well as the nitrification (bacterial and archaeal amoA) and denitrification (nirS, nirK, nosZI, nosZII) genes involved in the generation or reduction of the greenhouse gas nitrous oxide. Detection and quantification thresholds were compared with those of quantitative real-time PCR and were equal to, or improved, in ddPCR. To validate the assays using environmental samples, soil DNA was isolated from two vineyards in the Okanagan valley in British Columbia, Canada, over the 2017 growing season. Soil properties related to the observed gene abundances were determined. Total bacteria, nirK, and nosZII increased with time and the soil C/N ratio and NH4+-N concentration affected total archaea and archaeal amoA negatively. The results, compared with those of other studies, showed that ddPCR is a valid alternative to qPCR to quantify genes involved in nitrification or denitrification.
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Affiliation(s)
- Tanja M Voegel
- Irving K. Barber Faculty of Science, Department of Biology, University of British Columbia Okanagan, 1177 Research Road, Kelowna, BC V1V 1V7, Canada.,Irving K. Barber Faculty of Science, Department of Biology, University of British Columbia Okanagan, 1177 Research Road, Kelowna, BC V1V 1V7, Canada
| | - Melissa M Larrabee
- Irving K. Barber Faculty of Science, Department of Biology, University of British Columbia Okanagan, 1177 Research Road, Kelowna, BC V1V 1V7, Canada.,Irving K. Barber Faculty of Science, Department of Biology, University of British Columbia Okanagan, 1177 Research Road, Kelowna, BC V1V 1V7, Canada
| | - Louise M Nelson
- Irving K. Barber Faculty of Science, Department of Biology, University of British Columbia Okanagan, 1177 Research Road, Kelowna, BC V1V 1V7, Canada.,Irving K. Barber Faculty of Science, Department of Biology, University of British Columbia Okanagan, 1177 Research Road, Kelowna, BC V1V 1V7, Canada
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20
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Lindström K, Mousavi SA. Effectiveness of nitrogen fixation in rhizobia. Microb Biotechnol 2020; 13:1314-1335. [PMID: 31797528 PMCID: PMC7415380 DOI: 10.1111/1751-7915.13517] [Citation(s) in RCA: 130] [Impact Index Per Article: 32.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2019] [Revised: 11/13/2019] [Accepted: 11/13/2019] [Indexed: 12/01/2022] Open
Abstract
Biological nitrogen fixation in rhizobia occurs primarily in root or stem nodules and is induced by the bacteria present in legume plants. This symbiotic process has fascinated researchers for over a century, and the positive effects of legumes on soils and their food and feed value have been recognized for thousands of years. Symbiotic nitrogen fixation uses solar energy to reduce the inert N2 gas to ammonia at normal temperature and pressure, and is thus today, especially, important for sustainable food production. Increased productivity through improved effectiveness of the process is seen as a major research and development goal. The interaction between rhizobia and their legume hosts has thus been dissected at agronomic, plant physiological, microbiological and molecular levels to produce ample information about processes involved, but identification of major bottlenecks regarding efficiency of nitrogen fixation has proven to be complex. We review processes and results that contributed to the current understanding of this fascinating system, with focus on effectiveness of nitrogen fixation in rhizobia.
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Affiliation(s)
- Kristina Lindström
- Faculty of Biological and Environmental Sciences and Helsinki Institute of Sustainability Science (HELSUS)University of HelsinkiFI‐00014HelsinkiFinland
| | - Seyed Abdollah Mousavi
- Faculty of Biological and Environmental Sciences and Helsinki Institute of Sustainability Science (HELSUS)University of HelsinkiFI‐00014HelsinkiFinland
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21
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Wasai-Hara S, Hara S, Morikawa T, Sugawara M, Takami H, Yoneda J, Tokunaga T, Minamisawa K. Diversity of Bradyrhizobium in Non-Leguminous Sorghum Plants: B. ottawaense Isolates Unique in Genes for N 2O Reductase and Lack of the Type VI Secretion System. Microbes Environ 2020; 35. [PMID: 31932539 PMCID: PMC7104290 DOI: 10.1264/jsme2.me19102] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Diverse members of Bradyrhizobium diazoefficiens, B. japonicum, and B. ottawaense were isolated from the roots of field-grown sorghum plants in Fukushima, and classified into “Rhizobia” with nodulated soybeans, “Free-living diazotrophs”, and “Non-diazotrophs” by nitrogen fixation and nodulation assays. Genome analyses revealed that B. ottawaense members possessed genes for N2O reduction, but lacked those for the Type VI secretion system (T6SS). T6SS is a new bacterial weapon against microbial competitors. Since T6SS-possessing B. diazoefficiens and B. japonicum have mainly been isolated from soybean nodules in Japan, T6SS-lacking B. ottawaense members may be a cryptic lineage of soybean bradyrhizobia in Japan.
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Affiliation(s)
| | | | | | | | - Hideto Takami
- Yokohama Institute, Japan Agency for Marine-Earth Science and Technology (JAMSTEC)
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22
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Woliy K, Degefu T, Frostegård Å. Host Range and Symbiotic Effectiveness of N 2O Reducing Bradyrhizobium Strains. Front Microbiol 2019; 10:2746. [PMID: 31849890 PMCID: PMC6896821 DOI: 10.3389/fmicb.2019.02746] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2019] [Accepted: 11/12/2019] [Indexed: 11/13/2022] Open
Abstract
Emissions of the potent greenhouse gas N2O is one of the environmental problems associated with intensive use of synthetic N fertilizers, and novel N2O mitigation strategies are needed to minimize fertilizer applications and N2O release without affecting agricultural efficiencies. Increased incorporation of legume crops in agricultural practices offers a sustainable alternative. Legumes, in their symbiosis with nitrogen fixing bacteria, rhizobia, reduce the need for fertilizers and also respond to the need for increased production of plant-based proteins. Not all combinations of rhizobia and legumes result in efficient nitrogen fixation, and legume crops therefore often need to be inoculated with compatible rhizobial strains. Recent research has demonstrated that some rhizobia are also very efficient N2O reducers. Several nutritionally and economically important legumes form root nodules in symbiosis with bacteria belonging to Bradyrhizobium. Here, the host-ranges of fourteen N2O reducing Bradyrhizobium strains were tested on six legume hosts; cowpea, groundnut, mung bean, haricot bean, soybean, and alfalfa. The plants were grown for 35 days in pots in sterile sand supplemented with N-free nutrient solution. Cowpea was the most promiscuous host nodulated by all test strains, followed by groundnut (11 strains) and mungbean (4 strains). Three test strains were able to nodulate all these three legumes, while none nodulated the other three hosts. For cowpea, five strains increased the shoot dry weight and ten strains the shoot nitrogen content (pairwise comparison; p < 0.05). For groundnut the corresponding results were three and nine strains. The symbiotic effectiveness for the different strains ranged from 45 to 98% in cowpea and 34 to 95% in groundnut, relative to fertilized controls. The N2O reduction capacity of detached nodules from cowpea plants inoculated with one of these strains confirmed active N2O reduction inside the nodules. When released from senescent nodules such strains are expected to also act as sinks for N2O produced by denitrifying organisms in the soil microbial community. Our strategy to search among known N2O-reducing Bradyrhizobium strains for their N2-fixation effectiveness successfully identified several strains which can potentially be used for the production of legume inoculants with the dual capacities of efficacious N2-fixation and N2O reduction.
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Affiliation(s)
- Kedir Woliy
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, Ås, Norway
| | - Tulu Degefu
- International Crops Research Institute for the Semi-Arid Tropics, Addis Ababa, Ethiopia
| | - Åsa Frostegård
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, Ås, Norway
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