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Li X, Li Z, Wei Y, Chen Z, Xie S. Identification and characterization of the TetR family transcriptional regulator NffT in Rhizobium johnstonii. Appl Environ Microbiol 2024; 90:e0185123. [PMID: 38426790 PMCID: PMC10952539 DOI: 10.1128/aem.01851-23] [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: 10/17/2023] [Accepted: 02/02/2024] [Indexed: 03/02/2024] Open
Abstract
Symbiotic nitrogen fixation (SNF) by rhizobia is not only the main natural bionitrogen-source for organisms but also a green process leveraged to increase the fertility of soil for agricultural production. However, an insufficient understanding of the regulatory mechanism of SNF hinders its practical application. During SNF, nifA-fixA signaling is essential for the biosynthesis of nitrogenases and electron transfer chain proteins. In the present study, the TetR regulator NffT, whose mutation increased fixA expression, was discovered through a fixA-promoter-β-glucuronidase fusion assay performed with Rhizobium johnstonii. Real-time quantitative PCR analysis showed that nffT deletion increased the expression of symbiotic genes including nifA and fixA in nifA-fixA signaling, and fixL, fixK, fnrN, and fixN9 in fixL-fixN signaling. nffT overexpression resulted in disordered nodules and reduced nitrogen-fixing efficiency. Electrophoretic mobility shift assays revealed that NffT directly regulated the transcription of RL0091-93, which encode an ATP-binding ABC transporter predicted to be involved in carbohydrate transport. Purified His-tagged NffT bound to a 68 bp DNA sequence located -32 to -99 bp upstream of RL0091-93 and NffT deletion significantly increased the expression of RL0091-93. nffT-promoter-β-glucuronidase fusion assay indicated that nffT expression was regulated by the cobNTS genes and cobalamin. Mutations in cobNTS significantly decreased the expression of nffT, and cobalamin restored its expression. These results revealed that NffT affects nodule development and nitrogen-fixing reaction by participating in a complex regulatory network of symbiotic and carbohydrate metabolic genes and, thus, plays a pivotal regulatory role during symbiosis of R. johnstonii-Pisum sativum.IMPORTANCESymbiotic nitrogen fixation (SNF) by rhizobia is a green way to maintain soil fertility without causing environmental pollution or consuming chemical energy. A detailed understanding of the regulatory mechanism of this complex process is essential for promoting sustainable agriculture. In this study, we discovered the TetR-type regulator NffT, which suppressed the expression of fixA in Rhizobium johnstonii. Furthermore, NffT was confirmed to play pleiotropic roles in R. johnstonii-Pisum sativum symbiosis; specifically, it inhibited rhizobial growth, nodule differentiation, and nitrogen-fixing reactions. We revealed that NffT indirectly affected R. johnstonii-P. sativum symbiosis by participating in a complex regulatory network of symbiotic and carbohydrate metabolic genes. Furthermore, cobalamin, a chemical molecule, was reported for the first time to be involved in TetR-type protein transcription during symbiosis. Thus, NffT identification connects SNF regulation with genetic, metabolic, and chemical signals and provides new insights into the complex regulation of SNF, laying an experimental basis for the targeted construction of rhizobial strains with highly efficient nitrogen-fixing capacity.
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Affiliation(s)
- Xiaofang Li
- Institute of Biopharmaceuticals, School of Pharmaceutical Sciences, Taizhou University, Taizhou, Zhejiang, China
| | - Zhangqun Li
- Institute of Biopharmaceuticals, School of Pharmaceutical Sciences, Taizhou University, Taizhou, Zhejiang, China
| | - Yajuan Wei
- Institute of Biopharmaceuticals, School of Pharmaceutical Sciences, Taizhou University, Taizhou, Zhejiang, China
| | - Zirui Chen
- Institute of Biopharmaceuticals, School of Pharmaceutical Sciences, Taizhou University, Taizhou, Zhejiang, China
| | - Shijie Xie
- Institute of Biopharmaceuticals, School of Pharmaceutical Sciences, Taizhou University, Taizhou, Zhejiang, China
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Li X, Li Z. What determines symbiotic nitrogen fixation efficiency in rhizobium: recent insights into Rhizobium leguminosarum. Arch Microbiol 2023; 205:300. [PMID: 37542687 DOI: 10.1007/s00203-023-03640-7] [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: 06/01/2023] [Revised: 07/21/2023] [Accepted: 07/24/2023] [Indexed: 08/07/2023]
Abstract
Symbiotic nitrogen fixation (SNF) by rhizobium, a Gram-negative soil bacterium, is an essential component in the nitrogen cycle and is a sustainable green way to maintain soil fertility without chemical energy consumption. SNF, which results from the processes of nodulation, rhizobial infection, bacteroid differentiation and nitrogen-fixing reaction, requires the expression of various genes from both symbionts with adaptation to the changing environment. To achieve successful nitrogen fixation, rhizobia and their hosts cooperate closely for precise regulation of symbiotic genes, metabolic processes and internal environment homeostasis. Many researches have progressed to reveal the ample information about regulatory aspects of SNF during recent decades, but the major bottlenecks regarding improvement of nitrogen-fixing efficiency has proven to be complex. In this mini-review, we summarize recent advances that have contributed to understanding the rhizobial regulatory aspects that determine SNF efficiency, focusing on the coordinated regulatory mechanism of symbiotic genes, oxygen, carbon metabolism, amino acid metabolism, combined nitrogen, non-coding RNAs and internal environment homeostasis. Unraveling regulatory determinants of SNF in the nitrogen-fixing protagonist rhizobium is expected to promote an improvement of nitrogen-fixing efficiency in crop production.
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Affiliation(s)
- Xiaofang Li
- Institute of Biopharmaceuticals, Taizhou University, 1139 Shifu Avenue, Taizhou, 318000, China.
- School of Pharmaceutical Sciences, Taizhou University, 1139 Shifu Avenue, Taizhou, 318000, China.
| | - Zhangqun Li
- School of Pharmaceutical Sciences, Taizhou University, 1139 Shifu Avenue, Taizhou, 318000, China
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3
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NoiD, a DedA membrane protein required for homeostasis maintaining of Rhizobium leguminosarum biovar viciae during symbiosis with Pisum sativum. Symbiosis 2022. [DOI: 10.1007/s13199-021-00827-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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4
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Wardell GE, Hynes MF, Young PJ, Harrison E. Why are rhizobial symbiosis genes mobile? Philos Trans R Soc Lond B Biol Sci 2022; 377:20200471. [PMID: 34839705 PMCID: PMC8628070 DOI: 10.1098/rstb.2020.0471] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2021] [Accepted: 07/28/2021] [Indexed: 11/12/2022] Open
Abstract
Rhizobia are one of the most important and best studied groups of bacterial symbionts. They are defined by their ability to establish nitrogen-fixing intracellular infections within plant hosts. One surprising feature of this symbiosis is that the bacterial genes required for this complex trait are not fixed within the chromosome, but are encoded on mobile genetic elements (MGEs), namely plasmids or integrative and conjugative elements. Evidence suggests that many of these elements are actively mobilizing within rhizobial populations, suggesting that regular symbiosis gene transfer is part of the ecology of rhizobial symbionts. At first glance, this is counterintuitive. The symbiosis trait is highly complex, multipartite and tightly coevolved with the legume hosts, while transfer of genes can be costly and disrupt coadaptation between the chromosome and the symbiosis genes. However, horizontal gene transfer is a process driven not only by the interests of the host bacterium, but also, and perhaps predominantly, by the interests of the MGEs that facilitate it. Thus understanding the role of horizontal gene transfer in the rhizobium-legume symbiosis requires a 'mobile genetic element's-eye view' on the ecology and evolution of this important symbiosis. This article is part of the theme issue 'The secret lives of microbial mobile genetic elements'.
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Affiliation(s)
- Grace E. Wardell
- Department of Animal Plant Sciences, University of Sheffield, Western Bank, Sheffield S10 1EA, UK
| | - Michael F. Hynes
- Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, Alberta, Canada T2N 1N4
| | - Peter J. Young
- Department of Biology, University of York, Wentworth Way, York YO10 5DD, UK
| | - Ellie Harrison
- Department of Animal Plant Sciences, University of Sheffield, Western Bank, Sheffield S10 1EA, UK
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Webb IUC, Xu J, Sánchez-Cañizares C, Karunakaran R, Ramachandran VK, Rutten PJ, East AK, Huang WE, Watmough NJ, Poole PS. Regulation and Characterization of Mutants of fixABCX in Rhizobium leguminosarum. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2021; 34:1167-1180. [PMID: 34110256 DOI: 10.1094/mpmi-02-21-0037-r] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Symbiosis between Rhizobium leguminosarum and Pisum sativum requires tight control of redox balance in order to maintain respiration under the microaerobic conditions required for nitrogenase while still producing the eight electrons and sixteen molecules of ATP needed for nitrogen fixation. FixABCX, a cluster of electron transfer flavoproteins essential for nitrogen fixation, is encoded on the Sym plasmid (pRL10), immediately upstream of nifA, which encodes the general transcriptional regulator of nitrogen fixation. There is a symbiotically regulated NifA-dependent promoter upstream of fixA (PnifA1), as well as an additional basal constitutive promoter driving background expression of nifA (PnifA2). These were confirmed by 5'-end mapping of transcription start sites using differential RNA-seq. Complementation of polar fixAB and fixX mutants (Fix- strains) confirmed expression of nifA from PnifA1 in symbiosis. Electron microscopy combined with single-cell Raman microspectroscopy characterization of fixAB mutants revealed previously unknown heterogeneity in bacteroid morphology within a single nodule. Two morphotypes of mutant fixAB bacteroids were observed. One was larger than wild-type bacteroids and contained high levels of polyhydroxy-3-butyrate, a complex energy/reductant storage product. A second bacteroid phenotype was morphologically and compositionally different and resembled wild-type infection thread cells. From these two characteristic fixAB mutant bacteroid morphotypes, inferences can be drawn on the metabolism of wild-type nitrogen-fixing bacteroids.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.
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Affiliation(s)
- Isabel U C Webb
- Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, U.K
- Department of Molecular Microbiology, John Innes Centre, Norwich Research Park, Norwich NR4 7UH, U.K
| | - Jiabao Xu
- Department of Engineering, University of Oxford, Parks Road, Oxford OX1 3PJ, U.K
| | | | - Ramakrishnan Karunakaran
- Department of Molecular Microbiology, John Innes Centre, Norwich Research Park, Norwich NR4 7UH, U.K
| | - Vinoy K Ramachandran
- Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, U.K
| | - Paul J Rutten
- Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, U.K
| | - Alison K East
- Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, U.K
| | - Wei E Huang
- Department of Engineering, University of Oxford, Parks Road, Oxford OX1 3PJ, U.K
| | - Nicholas J Watmough
- School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich, Norfolk NR4 7TJ, U.K
| | - Philip S Poole
- Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, U.K
- Department of Molecular Microbiology, John Innes Centre, Norwich Research Park, Norwich NR4 7UH, U.K
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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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Multiple sensors provide spatiotemporal oxygen regulation of gene expression in a Rhizobium-legume symbiosis. PLoS Genet 2021; 17:e1009099. [PMID: 33539353 PMCID: PMC7888657 DOI: 10.1371/journal.pgen.1009099] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2020] [Revised: 02/17/2021] [Accepted: 12/04/2020] [Indexed: 01/04/2023] Open
Abstract
Regulation by oxygen (O2) in rhizobia is essential for their symbioses with plants and involves multiple O2 sensing proteins. Three sensors exist in the pea microsymbiont Rhizobium leguminosarum Rlv3841: hFixL, FnrN and NifA. At low O2 concentrations (1%) hFixL signals via FxkR to induce expression of the FixK transcription factor, which activates transcription of downstream genes. These include fixNOQP, encoding the high-affinity cbb3-type terminal oxidase used in symbiosis. In free-living Rlv3841, the hFixL-FxkR-FixK pathway was active at 1% O2, and confocal microscopy showed hFixL-FxkR-FixK activity in the earliest stages of Rlv3841 differentiation in nodules (zones I and II). Work on Rlv3841 inside and outside nodules showed that the hFixL-FxkR-FixK pathway also induces transcription of fnrN at 1% O2 and in the earliest stages of Rlv3841 differentiation in nodules. We confirmed past findings suggesting a role for FnrN in fixNOQP expression. However, unlike hFixL-FxkR-FixK, Rlv3841 FnrN was only active in the near-anaerobic zones III and IV of pea nodules. Quantification of fixNOQP expression in nodules showed this was driven primarily by FnrN, with minimal direct hFixL-FxkR-FixK induction. Thus, FnrN is key for full symbiotic expression of fixNOQP. Without FnrN, nitrogen fixation was reduced by 85% in Rlv3841, while eliminating hFixL only reduced fixation by 25%. The hFixL-FxkR-FixK pathway effectively primes the O2 response by increasing fnrN expression in early differentiation (zones I-II). In zone III of mature nodules, near-anaerobic conditions activate FnrN, which induces fixNOQP transcription to the level required for wild-type nitrogen fixation activity. Modelling and transcriptional analysis indicates that the different O2 sensitivities of hFixL and FnrN lead to a nuanced spatiotemporal pattern of gene regulation in different nodule zones in response to changing O2 concentration. Multi-sensor O2 regulation is prevalent in rhizobia, suggesting the fine-tuned control this enables is common and maximizes the effectiveness of the symbioses. Rhizobia are soil bacteria that form a symbiosis with legume plants. In exchange for shelter from the plant, rhizobia provide nitrogen fertilizer, produced by nitrogen fixation. Fixation is catalysed by the nitrogenase enzyme, which is inactivated by oxygen. To prevent this, plants house rhizobia in root nodules, which create a low oxygen environment. However, rhizobia need oxygen, and must adapt to survive the low oxygen concentration in the nodule. Key to this is regulating their genes based on oxygen concentration. We studied one Rhizobium species which uses three different protein sensors of oxygen, each turning on at a different oxygen concentration. As the bacteria get deeper inside the plant nodule and the oxygen concentration drops, each sensor switches on in turn. Our results also show that the first sensor to turn on, hFixL, primes the second sensor, FnrN. This prepares the rhizobia for the core region of the nodule where oxygen concentration is lowest and most nitrogen fixation takes place. If both sensors are removed, the bacteria cannot fix nitrogen. Many rhizobia have several oxygen sensing proteins, so using multiple sensors is likely a common strategy enabling rhizobia to adapt to low oxygen precisely and in stages during symbiosis.
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Rodríguez S, Correa-Galeote D, Sánchez-Pérez M, Ramírez M, Isidra-Arellano MC, Reyero-Saavedra MDR, Zamorano-Sánchez D, Hernández G, Valdés-López O, Girard L. A Novel OmpR-Type Response Regulator Controls Multiple Stages of the Rhizobium etli - Phaseolus vulgaris N 2-Fixing Symbiosis. Front Microbiol 2021; 11:615775. [PMID: 33384681 PMCID: PMC7769827 DOI: 10.3389/fmicb.2020.615775] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2020] [Accepted: 11/26/2020] [Indexed: 11/22/2022] Open
Abstract
OmpR, is one of the best characterized response regulators families, which includes transcriptional regulators with a variety of physiological roles including the control of symbiotic nitrogen fixation (SNF). The Rhizobium etli CE3 genome encodes 18 OmpR-type regulators; the function of the majority of these regulators during the SNF in common bean, remains elusive. In this work, we demonstrated that a R. etli mutant strain lacking the OmpR-type regulator RetPC57 (ΔRetPC57), formed less nodules when used as inoculum for common bean. Furthermore, we observed reduced expression level of bacterial genes involved in Nod Factors production (nodA and nodB) and of plant early-nodulation genes (NSP2, NIN, NF-YA and ENOD40), in plants inoculated with ΔRetPC57. RetPC57 also contributes to the appropriate expression of genes which products are part of the multidrug efflux pumps family (MDR). Interestingly, nodules elicited by ΔRetPC57 showed increased expression of genes relevant for Carbon/Nitrogen nodule metabolism (PEPC and GOGAT) and ΔRetPC57 bacteroids showed higher nitrogen fixation activity as well as increased expression of key genes directly involved in SNF (hfixL, fixKf, fnrN, fixN, nifA and nifH). Taken together, our data show that the previously uncharacterized regulator RetPC57 is a key player in the development of the R. etli - P. vulgaris symbiosis.
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Affiliation(s)
- Susana Rodríguez
- Programa de Biología de Sistemas y Biología Sintética, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Mexico
| | - David Correa-Galeote
- Programa de Biología de Sistemas y Biología Sintética, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Mexico
| | - Mishael Sánchez-Pérez
- Programa de Biología de Sistemas y Biología Sintética, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Mexico.,Programa de Genómica Computacional, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Mexico
| | - Mario Ramírez
- Programa de Genómica Funcional de Eucariontes, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Mexico
| | - Mariel C Isidra-Arellano
- Laboratorio de Genómica Funcional de Leguminosas, Facultad de Estudios Superiores Iztacala, Universidad Nacional Autónoma de México, Tlalnepantla de Baz, Mexico
| | - María Del Rocío Reyero-Saavedra
- Laboratorio de Genómica Funcional de Leguminosas, Facultad de Estudios Superiores Iztacala, Universidad Nacional Autónoma de México, Tlalnepantla de Baz, Mexico
| | - David Zamorano-Sánchez
- Programa de Biología de Sistemas y Biología Sintética, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Mexico
| | - Georgina Hernández
- Programa de Genómica Funcional de Eucariontes, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Mexico
| | - Oswaldo Valdés-López
- Laboratorio de Genómica Funcional de Leguminosas, Facultad de Estudios Superiores Iztacala, Universidad Nacional Autónoma de México, Tlalnepantla de Baz, Mexico
| | - Lourdes Girard
- Programa de Biología de Sistemas y Biología Sintética, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Mexico
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Lipa P, Janczarek M. Phosphorylation systems in symbiotic nitrogen-fixing bacteria and their role in bacterial adaptation to various environmental stresses. PeerJ 2020; 8:e8466. [PMID: 32095335 PMCID: PMC7020829 DOI: 10.7717/peerj.8466] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2019] [Accepted: 12/27/2019] [Indexed: 12/23/2022] Open
Abstract
Symbiotic bacteria, commonly called rhizobia, lead a saprophytic lifestyle in the soil and form nitrogen-fixing nodules on legume roots. During their lifecycle, rhizobia have to adapt to different conditions prevailing in the soils and within host plants. To survive under these conditions, rhizobia fine-tune the regulatory machinery to respond rapidly and adequately to environmental changes. Symbiotic bacteria play an essential role in the soil environment from both ecological and economical point of view, since these bacteria provide Fabaceae plants (legumes) with large amounts of accessible nitrogen as a result of symbiotic interactions (i.e., rhizobia present within the nodule reduce atmospheric dinitrogen (N2) to ammonia, which can be utilized by plants). Because of its restricted availability in the soil, nitrogen is one of the most limiting factors for plant growth. In spite of its high content in the atmosphere, plants are not able to assimilate it directly in the N2 form. During symbiosis, rhizobia infect host root and trigger the development of specific plant organ, the nodule. The aim of root nodule formation is to ensure a microaerobic environment, which is essential for proper activity of nitrogenase, i.e., a key enzyme facilitating N2 fixation. To adapt to various lifestyles and environmental stresses, rhizobia have developed several regulatory mechanisms, e.g., reversible phosphorylation. This key mechanism regulates many processes in both prokaryotic and eukaryotic cells. In microorganisms, signal transduction includes two-component systems (TCSs), which involve membrane sensor histidine kinases (HKs) and cognate DNA-binding response regulators (RRs). Furthermore, regulatory mechanisms based on phosphoenolopyruvate-dependent phosphotranspherase systems (PTSs), as well as alternative regulatory pathways controlled by Hanks-type serine/threonine kinases (STKs) and serine/threonine phosphatases (STPs) play an important role in regulation of many cellular processes in both free-living bacteria and during symbiosis with the host plant (e.g., growth and cell division, envelope biogenesis, biofilm formation, response to stress conditions, and regulation of metabolism). In this review, we summarize the current knowledge of phosphorylation systems in symbiotic nitrogen-fixing bacteria, and their role in the physiology of rhizobial cells and adaptation to various environmental conditions.
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Affiliation(s)
- Paulina Lipa
- Department of Genetics and Microbiology, Institute of Biological Sciences, Maria Curie-Sklodowska University Lublin, Lublin, Poland
| | - Monika Janczarek
- Department of Genetics and Microbiology, Institute of Biological Sciences, Maria Curie-Sklodowska University Lublin, Lublin, Poland
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Abstract
Rhizobia are α- and β-proteobacteria that form a symbiotic partnership with legumes, fixing atmospheric dinitrogen to ammonia and providing it to the plant. Oxygen regulation is key in this symbiosis. Fixation is performed by an oxygen-intolerant nitrogenase enzyme but requires respiration to meet its high energy demands. To satisfy these opposing constraints the symbiotic partners cooperate intimately, employing a variety of mechanisms to regulate and respond to oxygen concentration. During symbiosis rhizobia undergo significant changes in gene expression to differentiate into nitrogen-fixing bacteroids. Legumes host these bacteroids in specialized root organs called nodules. These generate a near-anoxic environment using an oxygen diffusion barrier, oxygen-binding leghemoglobin and control of mitochondria localization. Rhizobia sense oxygen using multiple interconnected systems which enable a finely-tuned response to the wide range of oxygen concentrations they experience when transitioning from soil to nodules. The oxygen-sensing FixL-FixJ and hybrid FixL-FxkR two-component systems activate at relatively high oxygen concentration and regulate fixK transcription. FixK activates the fixNOQP and fixGHIS operons producing a high-affinity terminal oxidase required for bacterial respiration in the microaerobic nodule. Additionally or alternatively, some rhizobia regulate expression of these operons by FnrN, an FNR-like oxygen-sensing protein. The final stage of symbiotic establishment is activated by the NifA protein, regulated by oxygen at both the transcriptional and protein level. A cross-species comparison of these systems highlights differences in their roles and interconnections but reveals common regulatory patterns and themes. Future work is needed to establish the complete regulon of these systems and identify other regulatory signals.
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Affiliation(s)
- Paul J Rutten
- Department of Plant Sciences, University of Oxford, Oxford, United Kingdom
| | - Philip S Poole
- Department of Plant Sciences, University of Oxford, Oxford, United Kingdom
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11
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Guimarães WG, Gondim ACS, Costa PMDS, Gilles-Gonzalez MA, Lopes LGF, Carepo MSP, Sousa EHS. Insights into signal transduction by a hybrid FixL: Denaturation study of on and off states of a multi-domain oxygen sensor. J Inorg Biochem 2017; 172:129-137. [PMID: 28458146 DOI: 10.1016/j.jinorgbio.2017.04.013] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2016] [Revised: 03/21/2017] [Accepted: 04/02/2017] [Indexed: 11/17/2022]
Abstract
FixL from Rhizobium etli (ReFixL) is a hybrid oxygen sensor protein. Signal transduction in ReFixL is effected by a switch off of the kinase activity on binding of an oxygen molecule to ferrous heme iron in another domain. Cyanide can also inhibit the kinase activity upon binding to the heme iron in the ferric state. The unfolding by urea of the purified full-length ReFixL in both active pentacoordinate form, met-FixL(FeIII) and inactive cyanomet-FixL (FeIII-CN-) form was monitored by UV-visible absorption spectroscopy, circular dichroism (CD) and fluorescence spectroscopy. The CD and UV-visible absorption spectroscopy revealed two states during unfolding, whereas fluorescence spectroscopy identified a three-state unfolding mechanism. The unfolding mechanism was not altered for the active compared to the inactive state; however, differences in the ΔGH2O were observed. According to the CD results, compared to cyanomet-FixL, met-FixL was more stable towards chemical denaturation by urea (7.2 vs 4.8kJmol-1). By contrast, electronic spectroscopy monitoring of the Soret band showed cyanomet-FixL to be more stable than met-FixL (18.5 versus 36.2kJmol-1). For the three-state mechanism exhibited by fluorescence, the ΔGH2O for both denaturation steps were higher for the active-state met-FixL than for cyanomet-FixL. The overall stability of met-FixL is higher in comparison to cyanomet-FixL suggesting a more compact protein in the active form. Nonetheless, hydrogen bonding by bound cyanide in the inactive state promotes the stability of the heme domain. This work supports a model of signal transduction by FixL that is likely shared by other heme-based sensors.
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Affiliation(s)
- Wellinson G Guimarães
- Laboratório de Bioinorgânica, Departamento de Química Orgânica e Inorgânica, Universidade Federal do Ceará, CEP 60455-760 Fortaleza, Ceará, Brazil
| | - Ana C S Gondim
- Laboratório de Bioinorgânica, Departamento de Química Orgânica e Inorgânica, Universidade Federal do Ceará, CEP 60455-760 Fortaleza, Ceará, Brazil
| | - Pedro Mikael da Silva Costa
- Laboratório de Bioinorgânica, Departamento de Química Orgânica e Inorgânica, Universidade Federal do Ceará, CEP 60455-760 Fortaleza, Ceará, Brazil
| | - Marie-Alda Gilles-Gonzalez
- Department of Biochemistry, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-9038, United States
| | - Luiz G F Lopes
- Laboratório de Bioinorgânica, Departamento de Química Orgânica e Inorgânica, Universidade Federal do Ceará, CEP 60455-760 Fortaleza, Ceará, Brazil
| | - Marta S P Carepo
- Laboratório de Bioinorgânica, Departamento de Química Orgânica e Inorgânica, Universidade Federal do Ceará, CEP 60455-760 Fortaleza, Ceará, Brazil.
| | - Eduardo H S Sousa
- Laboratório de Bioinorgânica, Departamento de Química Orgânica e Inorgânica, Universidade Federal do Ceará, CEP 60455-760 Fortaleza, Ceará, Brazil.
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Tsoy OV, Ravcheev DA, Čuklina J, Gelfand MS. Nitrogen Fixation and Molecular Oxygen: Comparative Genomic Reconstruction of Transcription Regulation in Alphaproteobacteria. Front Microbiol 2016; 7:1343. [PMID: 27617010 PMCID: PMC4999443 DOI: 10.3389/fmicb.2016.01343] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2016] [Accepted: 08/15/2016] [Indexed: 11/13/2022] Open
Abstract
Biological nitrogen fixation plays a crucial role in the nitrogen cycle. An ability to fix atmospheric nitrogen, reducing it to ammonium, was described for multiple species of Bacteria and Archaea. The transcriptional regulatory network for nitrogen fixation was extensively studied in several representatives of the class Alphaproteobacteria. This regulatory network includes the activator of nitrogen fixation NifA, working in tandem with the alternative sigma-factor RpoN as well as oxygen-responsive regulatory systems, one-component regulators FnrN/FixK and two-component system FixLJ. Here we used a comparative genomics approach for in silico study of the transcriptional regulatory network in 50 genomes of Alphaproteobacteria. We extended the known regulons and proposed the scenario for the evolution of the nitrogen fixation transcriptional network. The reconstructed network substantially expands the existing knowledge of transcriptional regulation in nitrogen-fixing microorganisms and can be used for genetic experiments, metabolic reconstruction, and evolutionary analysis.
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Affiliation(s)
- Olga V Tsoy
- Research and Training Center on Bioinformatics, A.A. Kharkevich Institute for Information Transmission Problems, Russian Academy of Sciences Moscow, Russia
| | - Dmitry A Ravcheev
- Luxembourg Centre for Systems Biomedicine, University of Luxembourg Esch-sur-Alzette, Luxembourg
| | - Jelena Čuklina
- Research and Training Center on Bioinformatics, A.A. Kharkevich Institute for Information Transmission Problems, Russian Academy of SciencesMoscow, Russia; Moscow Institute of Physics and TechnologyDolgoprudny, Russia
| | - Mikhail S Gelfand
- Research and Training Center on Bioinformatics, A.A. Kharkevich Institute for Information Transmission Problems, Russian Academy of SciencesMoscow, Russia; Faculty of Bioengineering and Bioinformatics, Moscow State UniversityMoscow, Russia; Skolkovo Institute of Science and TechnologySkolkovo, Russia; Faculty of Computer Science, Higher School of EconomicsMoscow, Russia
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13
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Reyes-González A, Talbi C, Rodríguez S, Rivera P, Zamorano-Sánchez D, Girard L. Expanding the regulatory network that controls nitrogen fixation in Sinorhizobium meliloti: elucidating the role of the two-component system hFixL-FxkR. MICROBIOLOGY-SGM 2016; 162:979-988. [PMID: 27010660 DOI: 10.1099/mic.0.000284] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
In Sinorhizobium meliloti, nitrogen fixation is regulated in response to oxygen concentration through the FixL-FixJ two-component system (TCS). Besides this conserved TCS, the field isolate SM11 also encodes the hFixL-FxkR TCS, which is responsible for the microoxic response in Rhizobium etli. Through genetic and physiological assays, we evaluated the role of the hFixL-FxkR TCS in S. meliloti SM11. Our results revealed that this regulatory system activates the expression of a fixKf orthologue (fixKa), in response to low oxygen concentration. Null mutations in either hFixL or FxkR promote upregulation of fixK1, a direct target of FixJ. Furthermore, the absence of this TCS translates into higher nitrogen fixation values as well as higher expression of fixN1 in nodules. Individual mutations in each of the fixK-like regulators encoded in the S. meliloti SM11 genome do not completely restrict fixN1 or fixN2 expression, pointing towards redundancy among these regulators. Both copies of fixN are necessary to achieve optimal levels of nitrogen fixation. This work provides evidence that the hFixL-FxkR TCS is activated in response to low oxygen concentration in S. meliloti SM11 and that it negatively regulates the expression of fixK1, fixN1 and nitrogen fixation.
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Affiliation(s)
- Alma Reyes-González
- Programa de Dinámica Genómica, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, Mexico.,Instituto de Investigaciones Básicas y Aplicadas, Universidad Autónoma del Estado de Morelos, Cuernavaca, Morelos, Mexico
| | - Chouhra Talbi
- Programa de Dinámica Genómica, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, Mexico
| | - Susana Rodríguez
- Programa de Dinámica Genómica, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, Mexico
| | - Patricia Rivera
- Programa de Dinámica Genómica, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, Mexico
| | - David Zamorano-Sánchez
- Department of Microbiology and Environmental Toxicology, University of California, Santa Cruz, USA
| | - Lourdes Girard
- Programa de Dinámica Genómica, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, Mexico
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Torres M, Simon J, Rowley G, Bedmar E, Richardson D, Gates A, Delgado M. Nitrous Oxide Metabolism in Nitrate-Reducing Bacteria: Physiology and Regulatory Mechanisms. Adv Microb Physiol 2016; 68:353-432. [PMID: 27134026 DOI: 10.1016/bs.ampbs.2016.02.007] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Nitrous oxide (N2O) is an important greenhouse gas (GHG) with substantial global warming potential and also contributes to ozone depletion through photochemical nitric oxide (NO) production in the stratosphere. The negative effects of N2O on climate and stratospheric ozone make N2O mitigation an international challenge. More than 60% of global N2O emissions are emitted from agricultural soils mainly due to the application of synthetic nitrogen-containing fertilizers. Thus, mitigation strategies must be developed which increase (or at least do not negatively impact) on agricultural efficiency whilst decrease the levels of N2O released. This aim is particularly important in the context of the ever expanding population and subsequent increased burden on the food chain. More than two-thirds of N2O emissions from soils can be attributed to bacterial and fungal denitrification and nitrification processes. In ammonia-oxidizing bacteria, N2O is formed through the oxidation of hydroxylamine to nitrite. In denitrifiers, nitrate is reduced to N2 via nitrite, NO and N2O production. In addition to denitrification, respiratory nitrate ammonification (also termed dissimilatory nitrate reduction to ammonium) is another important nitrate-reducing mechanism in soil, responsible for the loss of nitrate and production of N2O from reduction of NO that is formed as a by-product of the reduction process. This review will synthesize our current understanding of the environmental, regulatory and biochemical control of N2O emissions by nitrate-reducing bacteria and point to new solutions for agricultural GHG mitigation.
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15
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Hernández VM, Girard L, Hernández-Lucas I, Vázquez A, Ortíz-Ortíz C, Díaz R, Dunn MF. Genetic and biochemical characterization of arginine biosynthesis in Sinorhizobium meliloti 1021. Microbiology (Reading) 2015; 161:1671-1682. [DOI: 10.1099/mic.0.000122] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Affiliation(s)
- Victor M. Hernández
- Programa de Genómica Funcional de Procariotes, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos C. P. 62210, Mexico
| | - Lourdes Girard
- Programa de Dinámica Genómica, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos C. P. 62210, Mexico
| | - Ismael Hernández-Lucas
- Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos C. P. 62210, Mexico
| | - Alejandra Vázquez
- Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos C. P. 62210, Mexico
| | - Catalina Ortíz-Ortíz
- Programa de Genómica Funcional de Procariotes, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos C. P. 62210, Mexico
| | - Rafael Díaz
- Programa de Genómica Funcional de Procariotes, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos C. P. 62210, Mexico
| | - Michael F. Dunn
- Programa de Genómica Funcional de Procariotes, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos C. P. 62210, Mexico
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Rogel MA, Bustos P, Santamaría RI, González V, Romero D, Cevallos MÁ, Lozano L, Castro-Mondragón J, Martínez-Romero J, Ormeño-Orrillo E, Martínez-Romero E. Genomic basis of symbiovar mimosae in Rhizobium etli. BMC Genomics 2014; 15:575. [PMID: 25005495 PMCID: PMC4125696 DOI: 10.1186/1471-2164-15-575] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2013] [Accepted: 07/01/2014] [Indexed: 11/25/2022] Open
Abstract
Background Symbiosis genes (nod and nif) involved in nodulation and nitrogen fixation in legumes are plasmid-borne in Rhizobium. Rhizobial symbiotic variants (symbiovars) with distinct host specificity would depend on the type of symbiosis plasmid. In Rhizobium etli or in Rhizobium phaseoli, symbiovar phaseoli strains have the capacity to form nodules in Phaseolus vulgaris while symbiovar mimosae confers a broad host range including different mimosa trees. Results We report on the genome of R. etli symbiovar mimosae strain Mim1 and its comparison to that from R. etli symbiovar phaseoli strain CFN42. Differences were found in plasmids especially in the symbiosis plasmid, not only in nod gene sequences but in nod gene content. Differences in Nod factors deduced from the presence of nod genes, in secretion systems or ACC-deaminase could help explain the distinct host specificity. Genes involved in P. vulgaris exudate uptake were not found in symbiovar mimosae but hup genes (involved in hydrogen uptake) were found. Plasmid pRetCFN42a was partially contained in Mim1 and a plasmid (pRetMim1c) was found only in Mim1. Chromids were well conserved. Conclusions The genomic differences between the two symbiovars, mimosae and phaseoli may explain different host specificity. With the genomic analysis presented, the term symbiovar is validated. Furthermore, our data support that the generalist symbiovar mimosae may be older than the specialist symbiovar phaseoli. Electronic supplementary material The online version of this article (doi:10.1186/1471-2164-15-575) contains supplementary material, which is available to authorized users.
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Sousa EHS, Tuckerman JR, Gondim ACS, Gonzalez G, Gilles-Gonzalez MA. Signal Transduction and Phosphoryl Transfer by a FixL Hybrid Kinase with Low Oxygen Affinity: Importance of the Vicinal PAS Domain and Receiver Aspartate. Biochemistry 2013; 52:456-65. [DOI: 10.1021/bi300991r] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Eduardo H. S. Sousa
- Department of Organic and Inorganic
Chemistry, Federal University of Ceara,
Center for Sciences, CEP 60455-760 Fortaleza-Ceara, Brazil
| | - Jason R. Tuckerman
- Department of Biochemistry, University of Texas Southwestern Medical Center, 5323
Harry Hines Boulevard, Dallas, Texas 75390-9038, United States
| | - Ana C. S. Gondim
- Department of Biochemistry, University of Texas Southwestern Medical Center, 5323
Harry Hines Boulevard, Dallas, Texas 75390-9038, United States
| | - Gonzalo Gonzalez
- Department of Biochemistry, University of Texas Southwestern Medical Center, 5323
Harry Hines Boulevard, Dallas, Texas 75390-9038, United States
| | - Marie-Alda Gilles-Gonzalez
- Department of Biochemistry, University of Texas Southwestern Medical Center, 5323
Harry Hines Boulevard, Dallas, Texas 75390-9038, United States
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18
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Abstract
Symbiotic nitrogen fixation by rhizobia in legume root nodules injects approximately 40 million tonnes of nitrogen into agricultural systems each year. In exchange for reduced nitrogen from the bacteria, the plant provides rhizobia with reduced carbon and all the essential nutrients required for bacterial metabolism. Symbiotic nitrogen fixation requires exquisite integration of plant and bacterial metabolism. Central to this integration are transporters of both the plant and the rhizobia, which transfer elements and compounds across various plant membranes and the two bacterial membranes. Here we review current knowledge of legume and rhizobial transport and metabolism as they relate to symbiotic nitrogen fixation. Although all legume-rhizobia symbioses have many metabolic features in common, there are also interesting differences between them, which show that evolution has solved metabolic problems in different ways to achieve effective symbiosis in different systems.
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Affiliation(s)
- Michael Udvardi
- Plant Biology Division, Samuel Roberts Noble Foundation, Ardmore, OK 73401, USA.
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