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      Sinorhizobium fredii HH103 RirA Is Required for Oxidative Stress Resistance and Efficient Symbiosis with Soybean

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          Abstract

          Members of Rhizobiaceae contain a homologue of the iron-responsive regulatory protein RirA. In different bacteria, RirA acts as a repressor of iron uptake systems under iron-replete conditions and contributes to ameliorate cell damage during oxidative stress. In Rhizobium leguminosarum and Sinorhizobium meliloti, mutations in rirA do not impair symbiotic nitrogen fixation. In this study, a rirA mutant of broad host range S. fredii HH103 has been constructed (SVQ780) and its free-living and symbiotic phenotypes evaluated. No production of siderophores could be detected in either the wild-type or SVQ780. The rirA mutant exhibited a growth advantage under iron-deficient conditions and hypersensitivity to hydrogen peroxide in iron-rich medium. Transcription of rirA in HH103 is subject to autoregulation and inactivation of the gene upregulates fbpA, a gene putatively involved in iron transport. The S. fredii rirA mutant was able to nodulate soybean plants, but symbiotic nitrogen fixation was impaired. Nodules induced by the mutant were poorly infected compared to those induced by the wild-type. Genetic complementation reversed the mutant’s hypersensitivity to H 2O 2, expression of fbpA, and symbiotic deficiency in soybean plants. This is the first report that demonstrates a role for RirA in the Rhizobium-legume symbiosis.

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          Most cited references47

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          Bacterial iron homeostasis.

          Iron is essential to virtually all organisms, but poses problems of toxicity and poor solubility. Bacteria have evolved various mechanisms to counter the problems imposed by their iron dependence, allowing them to achieve effective iron homeostasis under a range of iron regimes. Highly efficient iron acquisition systems are used to scavenge iron from the environment under iron-restricted conditions. In many cases, this involves the secretion and internalisation of extracellular ferric chelators called siderophores. Ferrous iron can also be directly imported by the G protein-like transporter, FeoB. For pathogens, host-iron complexes (transferrin, lactoferrin, haem, haemoglobin) are directly used as iron sources. Bacterial iron storage proteins (ferritin, bacterioferritin) provide intracellular iron reserves for use when external supplies are restricted, and iron detoxification proteins (Dps) are employed to protect the chromosome from iron-induced free radical damage. There is evidence that bacteria control their iron requirements in response to iron availability by down-regulating the expression of iron proteins during iron-restricted growth. And finally, the expression of the iron homeostatic machinery is subject to iron-dependent global control ensuring that iron acquisition, storage and consumption are geared to iron availability and that intracellular levels of free iron do not reach toxic levels.
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            R factor transfer in Rhizobium leguminosarum.

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              Small mobilizable multi-purpose cloning vectors derived from the Escherichia coli plasmids pK18 and pK19: selection of defined deletions in the chromosome of Corynebacterium glutamicum

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                Author and article information

                Journal
                Int J Mol Sci
                Int J Mol Sci
                ijms
                International Journal of Molecular Sciences
                MDPI
                1422-0067
                12 February 2019
                February 2019
                : 20
                : 3
                : 787
                Affiliations
                [1 ]Departamento de Microbiología, Facultad de Biología, Universidad de Sevilla, Avda. Reina Mercedes 6, 41012 Sevilla, Spain; jccresporivas@ 123456gmail.com (J.C.C.-R.); pnavarro2@ 123456us.es (P.N.-G.); calias@ 123456us.es (C.A.-V.); cubo@ 123456us.es (T.C.); jvinar@ 123456us.es (J.M.V.); rsainz@ 123456us.es (J.E.R.-S.)
                [2 ]Daqing Branch of Heilongjiang Academy of Sciences, Daqing 163000, China; shijie0456@ 123456163.com
                [3 ]Institute of Microbiology, Heilongjiang Academy of Sciences, Harbin 150001, China; zhentao1212@ 123456126.com (T.Z.); lniuyanbo@ 123456163.com (Y.N.)
                [4 ]Departamento de Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, CSIC, c/ Profesor Albareda 1, 18008 Granada, Spain; virginia.cuellar@ 123456eez.csic.es
                [5 ]Departamento de Biología Celular, Facultad de Biología, Universidad de Sevilla, Avda. Reina Mercedes 6, 41012 Sevilla, Spain; onorato@ 123456us.es
                Author notes
                [* ]Correspondence: sacosta@ 123456us.es (S.A.-J.); mariajose.soto@ 123456eez.csic.es (M.J.S.); Tel.: +34-954-557121 (S.A.-J.); +34-958-181600 (M.J.S.)
                [†]

                These authors contributed equally to this work.

                Author information
                https://orcid.org/0000-0003-0217-199X
                https://orcid.org/0000-0001-7027-7126
                https://orcid.org/0000-0002-7105-5389
                https://orcid.org/0000-0002-5505-2508
                https://orcid.org/0000-0003-2045-7238
                Article
                ijms-20-00787
                10.3390/ijms20030787
                6386902
                30759803
                34bdf818-6587-404e-8bdf-8983831042a3
                © 2019 by the authors.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

                History
                : 14 January 2019
                : 09 February 2019
                Categories
                Article

                Molecular biology
                iron,rhizobium,regulation,siderophore,nitrogen-fixation,plant–bacteria interaction
                Molecular biology
                iron, rhizobium, regulation, siderophore, nitrogen-fixation, plant–bacteria interaction

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