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Anjou C, Lotoux A, Morvan C, Martin-Verstraete I. From ubiquity to specificity: The diverse functions of bacterial thioredoxin systems. Environ Microbiol 2024; 26:e16668. [PMID: 38899743 DOI: 10.1111/1462-2920.16668] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2024] [Accepted: 05/24/2024] [Indexed: 06/21/2024]
Abstract
The thioredoxin (Trx) system, found universally, is responsible for the regeneration of reversibly oxidized protein thiols in living cells. This system is made up of a Trx and a Trx reductase, and it plays a central role in maintaining thiol-based redox homeostasis by reducing oxidized protein thiols, such as disulfide bonds in proteins. Some Trxs also possess a chaperone function that is independent of thiol-disulfide exchange, in addition to their thiol-disulfide reductase activity. These two activities of the Trx system are involved in numerous physiological processes in bacteria. This review describes the diverse physiological roles of the Trx system that have emerged throughout bacterial evolution. The Trx system is essential for responding to oxidative and nitrosative stress. Beyond this primary function, the Trx system also participates in redox regulation and signal transduction, and in controlling metabolism, motility, biofilm formation, and virulence. This range of functions has evolved alongside the diversity of bacterial lifestyles and their specific constraints. This evolution can be characterized by the multiplication of the systems and by the specialization of cofactors or targets to adapt to the constraints of atypical lifestyles, such as photosynthesis, insect endosymbiosis, or spore-forming bacteria.
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Affiliation(s)
- Cyril Anjou
- Institut Pasteur, Université Paris Cité, UMR CNRS 6047, Laboratoire Pathogenèse des Bactéries Anaérobies, Paris, France
| | - Aurélie Lotoux
- Institut Pasteur, Université Paris Cité, UMR CNRS 6047, Laboratoire Pathogenèse des Bactéries Anaérobies, Paris, France
| | - Claire Morvan
- Institut Pasteur, Université Paris Cité, UMR CNRS 6047, Laboratoire Pathogenèse des Bactéries Anaérobies, Paris, France
| | - Isabelle Martin-Verstraete
- Institut Pasteur, Université Paris Cité, UMR CNRS 6047, Laboratoire Pathogenèse des Bactéries Anaérobies, Paris, France
- Institut Universitaire de France, Paris, France
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Zhang L, Zhao H, Qin S, Hu C, Shen Y, Qu B, Bai Y, Liu B. Genome-Resolved Metagenomics and Denitrifying Strain Isolation Reveal New Insights into Microbial Denitrification in the Deep Vadose Zone. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2024; 58:2323-2334. [PMID: 38267389 DOI: 10.1021/acs.est.3c06466] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2024]
Abstract
The heavy use of nitrogen fertilizer in intensive agricultural areas often leads to nitrate accumulation in subsurface soil and nitrate contamination in groundwater, which poses a serious risk to public health. Denitrifying microorganisms in the subsoil convert nitrate to gaseous forms of nitrogen, thereby mitigating the leaching of nitrate into groundwater. Here, we investigated denitrifying microorganisms in the deep vadose zone of a typical intensive agricultural area in China through microcosm enrichment, genome-resolved metagenomic analysis, and denitrifying bacteria isolation. A total of 1000 metagenome-assembled genomes (MAGs) were reconstructed, resulting in 98 high-quality, dereplicated MAGs that contained denitrification genes. Among them, 32 MAGs could not be taxonomically classified at the genus or species level, indicating that a broader spectrum of taxonomic groups is involved in subsoil denitrification than previously recognized. A denitrifier isolate library was constructed by using a strategy combining high-throughput and conventional cultivation techniques. Assessment of the denitrification characteristics of both the MAGs and isolates demonstrated the dominance of truncated denitrification. Functional screening revealed the highest denitrification activity in two complete denitrifiers belonging to the genus Pseudomonas. These findings greatly expand the current knowledge of the composition and function of denitrifying microorganisms in subsoils. The constructed isolate library provided the first pool of subsoil-denitrifying microorganisms that could facilitate the development of microbe-based technologies for nitrate attenuation in groundwater.
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Affiliation(s)
- Linqi Zhang
- Key Laboratory of Agricultural Water Resources, Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Shijiazhuang 050021, China
| | - Huicheng Zhao
- Key Laboratory of Agricultural Water Resources, Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Shijiazhuang 050021, China
| | - Shuping Qin
- Key Laboratory of Agricultural Water Resources, Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Shijiazhuang 050021, China
| | - Chunsheng Hu
- Key Laboratory of Agricultural Water Resources, Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Shijiazhuang 050021, China
| | - Yanjun Shen
- Key Laboratory of Agricultural Water Resources, Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Shijiazhuang 050021, China
| | - Baoyuan Qu
- State Key Laboratory of Plant Genomics, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China
- CAS-JIC Centre of Excellence for Plant and Microbial Sciences, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China
| | - Yang Bai
- State Key Laboratory of Plant Genomics, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China
- CAS-JIC Centre of Excellence for Plant and Microbial Sciences, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China
| | - Binbin Liu
- Key Laboratory of Agricultural Water Resources, Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Shijiazhuang 050021, China
- Xiong'an Institute of Innovation, Chinese Academy of Sciences, Xiong'an 071700, China
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Pathak PK, Yadav N, Kaladhar VC, Jaiswal R, Kumari A, Igamberdiev AU, Loake GJ, Gupta KJ. The emerging roles of nitric oxide and its associated scavengers-phytoglobins-in plant symbiotic interactions. JOURNAL OF EXPERIMENTAL BOTANY 2024; 75:563-577. [PMID: 37843034 DOI: 10.1093/jxb/erad399] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/09/2023] [Accepted: 10/09/2023] [Indexed: 10/17/2023]
Abstract
A key feature in the establishment of symbiosis between plants and microbes is the maintenance of the balance between the production of the small redox-related molecule, nitric oxide (NO), and its cognate scavenging pathways. During the establishment of symbiosis, a transition from a normoxic to a microoxic environment often takes place, triggering the production of NO from nitrite via a reductive production pathway. Plant hemoglobins [phytoglobins (Phytogbs)] are a central tenant of NO scavenging, with NO homeostasis maintained via the Phytogb-NO cycle. While the first plant hemoglobin (leghemoglobin), associated with the symbiotic relationship between leguminous plants and bacterial Rhizobium species, was discovered in 1939, most other plant hemoglobins, identified only in the 1990s, were considered as non-symbiotic. From recent studies, it is becoming evident that the role of Phytogbs1 in the establishment and maintenance of plant-bacterial and plant-fungal symbiosis is also essential in roots. Consequently, the division of plant hemoglobins into symbiotic and non-symbiotic groups becomes less justified. While the main function of Phytogbs1 is related to the regulation of NO levels, participation of these proteins in the establishment of symbiotic relationships between plants and microorganisms represents another important dimension among the other processes in which these key redox-regulatory proteins play a central role.
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Affiliation(s)
- Pradeep Kumar Pathak
- National Institute for Plant Genome Research, Aruna Asaf Ali Marg, New Delhi, India
| | - Nidhi Yadav
- National Institute for Plant Genome Research, Aruna Asaf Ali Marg, New Delhi, India
| | | | - Rekha Jaiswal
- National Institute for Plant Genome Research, Aruna Asaf Ali Marg, New Delhi, India
| | - Aprajita Kumari
- National Institute for Plant Genome Research, Aruna Asaf Ali Marg, New Delhi, India
| | - Abir U Igamberdiev
- Department of Biology, Memorial University of Newfoundland, St John's, NL, Canada
| | - Gary J Loake
- Institute of Molecular Plant Sciences, School of Biological Sciences, University of Edinburgh, Edinburgh EH9 3BF, UK
- Centre for Engineering Biology, School of Biological Sciences, University of Edinburgh, Edinburgh EH9 3BF, UK
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Oliveira MS, Santos KFDN, de Paula RM, Vitorino LC, Bessa LA, Greer A, Di Mascio P, de Souza JCP, Martin-Didonet CCG. Nitric Oxide Detection Using a Chemical Trap Method for Applications in Bacterial Systems. Microorganisms 2023; 11:2210. [PMID: 37764053 PMCID: PMC10536504 DOI: 10.3390/microorganisms11092210] [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: 07/20/2023] [Revised: 08/24/2023] [Accepted: 08/30/2023] [Indexed: 09/29/2023] Open
Abstract
Plant growth-promoting bacteria (PGPB) can be incorporated in biofertilizer formulations, which promote plant growth in different ways, such as fixing nitrogen and producing phytohormones and nitric oxide (NO). NO is a free radical involved in the growth and defense responses of plants and bacteria. NO detection is vital for further investigation in different agronomically important bacteria. NO production in the presence of KNO3 was evaluated over 1-3 days using eight bacterial strains, quantified by the usual Griess reaction, and monitored by 2,3-diaminonaphthalene (DAN), yielding 2,3-naphthotriazole (NAT), as analyzed by fluorescence spectroscopy, gas chromatography-mass spectrometry, and high-performance liquid chromatography. The Greiss and trapping reaction results showed that Azospirillum brasilense (HM053 and FP2), Rhizobium tropici (Br322), and Gluconacetobacter diazotrophicus (Pal 5) produced the highest NO levels 24 h after inoculation, whereas Nitrospirillum amazonense (Y2) and Herbaspirillum seropedicae (SmR1) showed no NO production. In contrast to the literature, in NFbHP-NH4Cl-lactate culture medium with KNO3, NO trapping led to the recovery of a product with a molecular mass ion of 182 Da, namely, 1,2,3,4-naphthotetrazole (NTT), which contained one more nitrogen atom than the usual NAT product with 169 Da. This strategy allows monitoring and tracking NO production in potential biofertilizing bacteria, providing future opportunities to better understand the mechanisms of bacteria-plant interaction and also to manipulate the amount of NO that will sustain the PGPB.
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Affiliation(s)
- Marilene Silva Oliveira
- Instituto Federal de Educação, Ciência e Tecnologia Goiano, Departamento de Agroquímica, Campus Rio Verde, Rio Verde 75901-970, GO, Brazil; (L.A.B.); (J.C.P.d.S.)
- Câmpus Henrique Santillo de Ciências Exatas e Tecnológicas Henrique Santillo, BR 153 n° 3105—Fazenda Barreiro do Meio, Anápolis 75132-903, GO, Brazil; (K.F.D.N.S.); (R.M.d.P.); (C.C.G.M.-D.)
- Simple Agro Corporation, rua Parque General Borges Forte, 400, Jardim Goiás, Rio Verde 75903-421, GO, Brazil
| | - Karina F. D. N. Santos
- Câmpus Henrique Santillo de Ciências Exatas e Tecnológicas Henrique Santillo, BR 153 n° 3105—Fazenda Barreiro do Meio, Anápolis 75132-903, GO, Brazil; (K.F.D.N.S.); (R.M.d.P.); (C.C.G.M.-D.)
| | - Railane Monteiro de Paula
- Câmpus Henrique Santillo de Ciências Exatas e Tecnológicas Henrique Santillo, BR 153 n° 3105—Fazenda Barreiro do Meio, Anápolis 75132-903, GO, Brazil; (K.F.D.N.S.); (R.M.d.P.); (C.C.G.M.-D.)
| | - Luciana C. Vitorino
- Instituto Federal de Educação, Ciência e Tecnologia Goiano, Departamento de Agroquímica, Campus Rio Verde, Rio Verde 75901-970, GO, Brazil; (L.A.B.); (J.C.P.d.S.)
- Simple Agro Corporation, rua Parque General Borges Forte, 400, Jardim Goiás, Rio Verde 75903-421, GO, Brazil
| | - Layara A. Bessa
- Instituto Federal de Educação, Ciência e Tecnologia Goiano, Departamento de Agroquímica, Campus Rio Verde, Rio Verde 75901-970, GO, Brazil; (L.A.B.); (J.C.P.d.S.)
- Simple Agro Corporation, rua Parque General Borges Forte, 400, Jardim Goiás, Rio Verde 75903-421, GO, Brazil
| | - Alexander Greer
- Department of Chemistry, Brooklyn College, City University of New York, Brooklyn, NY 11210, USA;
- The Graduate Center, City University of New York, New York, NY 10016, USA
| | - Paolo Di Mascio
- Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, São Paulo 05508-000, SP, Brazil;
| | - João C. P. de Souza
- Instituto Federal de Educação, Ciência e Tecnologia Goiano, Departamento de Agroquímica, Campus Rio Verde, Rio Verde 75901-970, GO, Brazil; (L.A.B.); (J.C.P.d.S.)
- Departamento de Química, Faculdade de Ciências, Universidade Estadual Paulista, Av. Eng. Luiz Edmundo Carrijo Coube, 14-01, São Paulo 17033-360, SP, Brazil
| | - Claudia C. G. Martin-Didonet
- Câmpus Henrique Santillo de Ciências Exatas e Tecnológicas Henrique Santillo, BR 153 n° 3105—Fazenda Barreiro do Meio, Anápolis 75132-903, GO, Brazil; (K.F.D.N.S.); (R.M.d.P.); (C.C.G.M.-D.)
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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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Pacheco PJ, Cabrera JJ, Jiménez-Leiva A, Torres MJ, Gates AJ, Bedmar EJ, Richardson DJ, Mesa S, Tortosa G, Delgado MJ. The copper-responsive regulator CsoR is indirectly involved in Bradyrhizobium diazoefficiens denitrification. FEMS Microbiol Lett 2023; 370:fnad084. [PMID: 37573143 PMCID: PMC10457146 DOI: 10.1093/femsle/fnad084] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2023] [Revised: 08/04/2023] [Accepted: 08/11/2023] [Indexed: 08/14/2023] Open
Abstract
The soybean endosymbiont Bradyrhizobium diazoefficiens harbours the complete denitrification pathway that is catalysed by a periplasmic nitrate reductase (Nap), a copper (Cu)-containing nitrite reductase (NirK), a c-type nitric oxide reductase (cNor), and a nitrous oxide reductase (Nos), encoded by the napEDABC, nirK, norCBQD, and nosRZDFYLX genes, respectively. Induction of denitrification genes requires low oxygen and nitric oxide, both signals integrated into a complex regulatory network comprised by two interconnected cascades, FixLJ-FixK2-NnrR and RegSR-NifA. Copper is a cofactor of NirK and Nos, but it has also a role in denitrification gene expression and protein synthesis. In fact, Cu limitation triggers a substantial down-regulation of nirK, norCBQD, and nosRZDFYLX gene expression under denitrifying conditions. Bradyrhizobium diazoefficiens genome possesses a gene predicted to encode a Cu-responsive repressor of the CsoR family, which is located adjacent to copA, a gene encoding a putative Cu+-ATPase transporter. To investigate the role of CsoR in the control of denitrification gene expression in response to Cu, a csoR deletion mutant was constructed in this work. Mutation of csoR did not affect the capacity of B. diazoefficiens to grow under denitrifying conditions. However, by using qRT-PCR analyses, we showed that nirK and norCBQD expression was much lower in the csoR mutant compared to wild-type levels under Cu-limiting denitrifying conditions. On the contrary, copA expression was significantly increased in the csoR mutant. The results obtained suggest that CsoR acts as a repressor of copA. Under Cu limitation, CsoR has also an indirect role in the expression of nirK and norCBQD genes.
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Affiliation(s)
- Pedro J Pacheco
- Department of Soil and Plant Microbiology, Estación Experimental del Zaidín, CSIC, C/Profesor Albareda 1, E-18008 Granada, Spain
| | - Juan J Cabrera
- Department of Soil and Plant Microbiology, Estación Experimental del Zaidín, CSIC, C/Profesor Albareda 1, E-18008 Granada, Spain
| | - Andrea Jiménez-Leiva
- Department of Soil and Plant Microbiology, Estación Experimental del Zaidín, CSIC, C/Profesor Albareda 1, E-18008 Granada, Spain
| | - María J Torres
- School of Biological Sciences, University of East Anglia, Norwich Research Park, Colney Lane, Norwich NR4 7TJ, United Kingdom
- Department of Biochemistry and Molecular Biology, Campus Universitario de Rabanales, University of Córdoba, Ed. C6, Planta Baja, 14071 Córdoba, Spain
| | - Andrew J Gates
- School of Biological Sciences, University of East Anglia, Norwich Research Park, Colney Lane, Norwich NR4 7TJ, United Kingdom
| | - Eulogio J Bedmar
- Department of Soil and Plant Microbiology, Estación Experimental del Zaidín, CSIC, C/Profesor Albareda 1, E-18008 Granada, Spain
| | - David J Richardson
- School of Biological Sciences, University of East Anglia, Norwich Research Park, Colney Lane, Norwich NR4 7TJ, United Kingdom
| | - Socorro Mesa
- Department of Soil and Plant Microbiology, Estación Experimental del Zaidín, CSIC, C/Profesor Albareda 1, E-18008 Granada, Spain
| | - Germán Tortosa
- Department of Soil and Plant Microbiology, Estación Experimental del Zaidín, CSIC, C/Profesor Albareda 1, E-18008 Granada, Spain
| | - María J Delgado
- Department of Soil and Plant Microbiology, Estación Experimental del Zaidín, CSIC, C/Profesor Albareda 1, E-18008 Granada, Spain
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Conte C, Apostolaki ET, Vizzini S, Migliore L. A Tight Interaction between the Native Seagrass Cymodocea nodosa and the Exotic Halophila stipulacea in the Aegean Sea Highlights Seagrass Holobiont Variations. PLANTS (BASEL, SWITZERLAND) 2023; 12:350. [PMID: 36679063 PMCID: PMC9863530 DOI: 10.3390/plants12020350] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/08/2022] [Revised: 01/03/2023] [Accepted: 01/05/2023] [Indexed: 06/17/2023]
Abstract
Seagrasses harbour bacterial communities with which they constitute a functional unit called holobiont that responds as a whole to environmental changes. Epiphytic bacterial communities rapidly respond to both biotic and abiotic factors, potentially contributing to the host fitness. The Lessepsian migrant Halophila stipulacea has a high phenotypical plasticity and harbours a highly diverse epiphytic bacterial community, which could support its invasiveness in the Mediterranean Sea. The current study aimed to evaluate the Halophila/Cymodocea competition in the Aegean Sea by analysing each of the two seagrasses in a meadow zone where these intermingled, as well as in their monospecific zones, at two depths. Differences in holobionts were evaluated using seagrass descriptors (morphometric, biochemical, elemental, and isotopic composition) to assess host changes, and 16S rRNA gene to identify bacterial community structure and composition. An Indicator Species Index was used to identify bacteria significantly associated with each host. In mixed meadows, native C. nodosa was shown to be affected by the presence of exotic H. stipulacea, in terms of both plant descriptors and bacterial communities, while H. stipulacea responded only to environmental factors rather than C. nodosa proximity. This study provided evidence of the competitive advantage of H. stipulacea on C. nodosa in the Aegean Sea and suggests the possible use of associated bacterial communities as an ecological seagrass descriptor.
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Affiliation(s)
- Chiara Conte
- PhD Program in Evolutionary Biology and Ecology, University of Rome Tor Vergata, 00133 Rome, Italy
- Laboratory of Ecology and Ecotoxicology, Department of Biology, University of Rome Tor Vergata, 00133 Rome, Italy
| | - Eugenia T. Apostolaki
- Institute of Oceanography, Hellenic Centre for Marine Research, P.O. Box 2214, 71003 Heraklion, Crete, Greece
| | - Salvatrice Vizzini
- Department of Earth and Marine Sciences, University of Palermo, Via Archirafi 18, 90123 Palermo, Italy
- CoNISMa, National Interuniversity Consortium for Marine Sciences, Piazzale Flaminio 9, 00196 Roma, Italy
| | - Luciana Migliore
- Laboratory of Ecology and Ecotoxicology, Department of Biology, University of Rome Tor Vergata, 00133 Rome, Italy
- eCampus University, Via Isimbardi 10, 22060 Novedrate (CO), Italy
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Pacheco PJ, Cabrera JJ, Jiménez-Leiva A, Bedmar EJ, Mesa S, Tortosa G, Delgado MJ. Effect of Copper on Expression of Functional Genes and Proteins Associated with Bradyrhizobium diazoefficiens Denitrification. Int J Mol Sci 2022; 23:ijms23063386. [PMID: 35328804 PMCID: PMC8951191 DOI: 10.3390/ijms23063386] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2022] [Revised: 03/16/2022] [Accepted: 03/17/2022] [Indexed: 12/16/2022] Open
Abstract
Nitrous oxide (N2O) is a powerful greenhouse gas that contributes to climate change. Denitrification is one of the largest sources of N2O in soils. The soybean endosymbiont Bradyrhizobium diazoefficiens is a model for rhizobial denitrification studies since, in addition to fixing N2, it has the ability to grow anaerobically under free-living conditions by reducing nitrate from the medium through the complete denitrification pathway. This bacterium contains a periplasmic nitrate reductase (Nap), a copper (Cu)-containing nitrite reductase (NirK), a c-type nitric oxide reductase (cNor), and a Cu-dependent nitrous oxide reductase (Nos) encoded by the napEDABC, nirK, norCBQD and nosRZDFYLX genes, respectively. In this work, an integrated study of the role of Cu in B. diazoefficiens denitrification has been performed. A notable reduction in nirK, nor, and nos gene expression observed under Cu limitation was correlated with a significant decrease in NirK, NorC and NosZ protein levels and activities. Meanwhile, nap expression was not affected by Cu, but a remarkable depletion in Nap activity was found, presumably due to an inhibitory effect of nitrite accumulated under Cu-limiting conditions. Interestingly, a post-transcriptional regulation by increasing Nap and NirK activities, as well as NorC and NosZ protein levels, was observed in response to high Cu. Our results demonstrate, for the first time, the role of Cu in transcriptional and post-transcriptional control of B. diazoefficiens denitrification. Thus, this study will contribute by proposing useful strategies for reducing N2O emissions from agricultural soils.
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