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The Sinorhizobium meliloti ntrX gene is involved in succinoglycan production, motility, and symbiotic nodulation on alfalfa. Appl Environ Microbiol 2013; 79:7150-9. [PMID: 24038694 DOI: 10.1128/aem.02225-13] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Rhizobia establish a symbiotic relationship with their host legumes to induce the formation of nitrogen-fixing nodules. This process is regulated by many rhizobium regulators, including some two-component regulatory systems (TCSs). NtrY/NtrX, a TCS that was first identified in Azorhizobium caulinodans, is required for free-living nitrogen metabolism and symbiotic nodulation on Sesbania rostrata. However, its functions in a typical rhizobium such as Sinorhizobium meliloti remain unclear. Here we found that the S. meliloti response regulator NtrX but not the histidine kinase NtrY is involved in the regulation of exopolysaccharide production, motility, and symbiosis with alfalfa. A plasmid insertion mutant of ntrX formed mucous colonies, which overproduced succinoglycan, an exopolysaccharide, by upregulating its biosynthesis genes. This mutant also exhibited motility defects due to reduced flagella and decreased expression of flagellins and regulatory genes. The regulation is independent of the known regulatory systems of ExoR/ExoS/ChvI, EmmABC, and ExpR. Alfalfa plants inoculated with the ntrX mutant were small and displayed symptoms of nitrogen starvation. Interestingly, the deletion mutant of ntrY showed a phenotype similar to that of the parent strain. These findings demonstrate that the S. meliloti NtrX is a new regulator of succinoglycan production and motility that is not genetically coupled with NtrY.
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Roset MS, Almirón MA. FixL-like sensor FlbS ofBrucella abortusbinds haem and is necessary for survival within eukaryotic cells. FEBS Lett 2013; 587:3102-7. [DOI: 10.1016/j.febslet.2013.07.047] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2013] [Revised: 07/23/2013] [Accepted: 07/29/2013] [Indexed: 11/27/2022]
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Characterization of an ntrX mutant of Neisseria gonorrhoeae reveals a response regulator that controls expression of respiratory enzymes in oxidase-positive proteobacteria. J Bacteriol 2013; 195:2632-41. [PMID: 23564168 DOI: 10.1128/jb.02062-12] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
NtrYX is a sensor-histidine kinase/response regulator two-component system that has had limited characterization in a small number of Alphaproteobacteria. Phylogenetic analysis of the response regulator NtrX showed that this two-component system is extensively distributed across the bacterial domain, and it is present in a variety of Betaproteobacteria, including the human pathogen Neisseria gonorrhoeae. Microarray analysis revealed that the expression of several components of the respiratory chain was reduced in an N. gonorrhoeae ntrX mutant compared to that in the isogenic wild-type (WT) strain 1291. These included the cytochrome c oxidase subunit (ccoP), nitrite reductase (aniA), and nitric oxide reductase (norB). Enzyme activity assays showed decreased cytochrome oxidase and nitrite reductase activities in the ntrX mutant, consistent with microarray data. N. gonorrhoeae ntrX mutants had reduced capacity to survive inside primary cervical cells compared to the wild type, and although they retained the ability to form a biofilm, they exhibited reduced survival within the biofilm compared to wild-type cells, as indicated by LIVE/DEAD staining. Analyses of an ntrX mutant in a representative alphaproteobacterium, Rhodobacter capsulatus, showed that cytochrome oxidase activity was also reduced compared to that in the wild-type strain SB1003. Taken together, these data provide evidence that the NtrYX two-component system may be a key regulator in the expression of respiratory enzymes and, in particular, cytochrome c oxidase, across a wide range of proteobacteria, including a variety of bacterial pathogens.
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Carrica MDC, Fernandez I, Sieira R, Paris G, Goldbaum FA. The two-component systems PrrBA and NtrYX co-ordinately regulate the adaptation ofBrucella abortusto an oxygen-limited environment. Mol Microbiol 2013; 88:222-33. [DOI: 10.1111/mmi.12181] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/09/2013] [Indexed: 01/13/2023]
Affiliation(s)
- Mariela del Carmen Carrica
- Laboratorio de Inmunología y Microbiología Molecular; Fundación Instituto Leloir (IIBBA-CONICET); Av. Patricias Argentinas 435; Buenos Aires; Argentina
| | - Ignacio Fernandez
- Laboratorio de Inmunología y Microbiología Molecular; Fundación Instituto Leloir (IIBBA-CONICET); Av. Patricias Argentinas 435; Buenos Aires; Argentina
| | - Rodrigo Sieira
- Laboratorio de Genética y Bioquímica de Rhizobacterias; Fundación Instituto Leloir (IIBBA-CONICET); Av. Patricias Argentinas 435; Buenos Aires; Argentina
| | - Gastón Paris
- Laboratorio de Inmunología y Microbiología Molecular; Fundación Instituto Leloir (IIBBA-CONICET); Av. Patricias Argentinas 435; Buenos Aires; Argentina
| | - Fernando Alberto Goldbaum
- Laboratorio de Inmunología y Microbiología Molecular; Fundación Instituto Leloir (IIBBA-CONICET); Av. Patricias Argentinas 435; Buenos Aires; Argentina
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RegA, the regulator of the two-component system RegB/RegA of Brucella suis, is a controller of both oxidative respiration and denitrification required for chronic infection in mice. Infect Immun 2013; 81:2053-61. [PMID: 23529617 DOI: 10.1128/iai.00063-13] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Adaptation to oxygen deficiency is essential for virulence and persistence of Brucella inside the host. The flexibility of this bacterium with respect to oxygen depletion is remarkable, since Brucella suis can use an oxygen-dependent transcriptional regulator of the FnrN family, two high-oxygen-affinity terminal oxidases, and a complete denitrification pathway to resist various conditions of oxygen deficiency. Moreover, our previous results suggested that oxidative respiration and denitrification can be simultaneously used by B. suis under microaerobiosis. The requirement of a functional cytochrome bd ubiquinol oxidase for nitrite reductase expression evidenced the linkage of these two pathways, and the central role of the two-component system RegB/RegA in the coordinated control of both respiratory systems was demonstrated. We propose a scheme for global regulation of B. suis respiratory pathways by the transcriptional regulator RegA, which postulates a role for the cytochrome bd ubiquinol oxidase in redox signal transmission to the histidine sensor kinase RegB. More importantly, RegA was found to be essential for B. suis persistence in vivo within oxygen-limited target organs. It is conceivable that RegA acts as a controller of numerous systems involved in the establishment of the persistent state, characteristic of chronic infections by Brucella.
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Aono S. The Dos family of globin-related sensors using PAS domains to accommodate haem acting as the active site for sensing external signals. Adv Microb Physiol 2013; 63:273-327. [PMID: 24054799 DOI: 10.1016/b978-0-12-407693-8.00007-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Sensor proteins play crucial roles in maintaining homeostasis of cells by sensing changes in extra- and intracellular chemical and physical conditions to trigger biological responses. It has recently become clear that gas molecules function as signalling molecules in these biological regulatory systems responsible for transcription, chemotaxis, synthesis/hydrolysis of nucleotide second messengers, and other complex physiological processes. Haem-containing sensor proteins are widely used to sense gas molecules because haem can bind gas molecules reversibly. Ligand binding to the haem in the sensor proteins triggers conformational changes around the haem, which results in their functional regulation. Spectroscopic and crystallographic studies are essential to understand how these sensor proteins function in these biological regulatory systems. In this chapter, I discuss structural and functional relationships of haem-containing PAS and PAS-related families of the sensor proteins.
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Mirabella A, Yañez Villanueva RM, Delrue RM, Uzureau S, Zygmunt MS, Cloeckaert A, De Bolle X, Letesson JJ. The two-component system PrlS/PrlR of Brucella melitensis is required for persistence in mice and appears to respond to ionic strength. MICROBIOLOGY-SGM 2012; 158:2642-2651. [PMID: 22859617 DOI: 10.1099/mic.0.060863-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Bacterial adaptation to environmental conditions is essential to ensure maximal fitness in the face of several stresses. In this context, two-component systems (TCSs) represent a predominant signal transduction mechanism, allowing an appropriate response to be mounted when a stimulus is sensed. As facultative intracellular pathogens, Brucella spp. face various environmental conditions, and an adequate response is required for a successful infection process. Recently, bioinformatic analysis of Brucella genomes predicted a set of 15 bona fide TCS pairs, among which some have been previously investigated. In this report, we characterized a new TCS locus called prlS/R, for probable proline sensor-regulator. It encodes a hybrid histidine kinase (PrlS) with an unusual Na(+)/solute symporter N-terminal domain and a transcriptional regulator (belonging to the LuxR family) (PrlR). In vitro, Brucella spp. with a functional PrlR/S system form bacterial aggregates, which seems to be an adaptive response to a hypersaline environment, while a prlS/R mutant does not. We identified ionic strength as a possible signal sensed by this TCS. Finally, this work correlates the absence of a functional PrlR/S system with the lack of hypersaline-induced aggregation in particular marine Brucella spp.
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Affiliation(s)
- Aurélie Mirabella
- Unité de Recherche en Biologie des Microorganismes (URBM), NARILIS, University of Namur (FUNDP), 61 rue de Bruxelles, B-5000 Namur, Belgium
| | - Rosse-Mary Yañez Villanueva
- Unité de Recherche en Biologie des Microorganismes (URBM), NARILIS, University of Namur (FUNDP), 61 rue de Bruxelles, B-5000 Namur, Belgium
| | - Rose-May Delrue
- Unité de Recherche en Biologie des Microorganismes (URBM), NARILIS, University of Namur (FUNDP), 61 rue de Bruxelles, B-5000 Namur, Belgium
| | - Sophie Uzureau
- Unité de Recherche en Biologie des Microorganismes (URBM), NARILIS, University of Namur (FUNDP), 61 rue de Bruxelles, B-5000 Namur, Belgium
| | - Michel S Zygmunt
- Université François Rabelais de Tours, UMR1282 Infectiologie et Santé Publique, F-37000 Tours, France.,INRA, UMR1282 Infectiologie et Santé Publique, F-37380 Nouzilly, France
| | - Axel Cloeckaert
- Université François Rabelais de Tours, UMR1282 Infectiologie et Santé Publique, F-37000 Tours, France.,INRA, UMR1282 Infectiologie et Santé Publique, F-37380 Nouzilly, France
| | - Xavier De Bolle
- Unité de Recherche en Biologie des Microorganismes (URBM), NARILIS, University of Namur (FUNDP), 61 rue de Bruxelles, B-5000 Namur, Belgium
| | - Jean-Jacques Letesson
- Unité de Recherche en Biologie des Microorganismes (URBM), NARILIS, University of Namur (FUNDP), 61 rue de Bruxelles, B-5000 Namur, Belgium
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Abstract
Brucella strains encounter oxygen deprivation during their intracellular replication in host cells, and the capacity of these bacteria to utilize NO(3) as an alternative electron acceptor for respiration plays an important role in their successful adaption to their intracellular niche. In this issue of Molecular Microbiology, Carrica et al (2012). report that NtrY and NtrX comprise a redox-responsive two-component regulator in Brucella abortus 2308 that responds to decreasing levels of O(2) and induces the expression of this strain's denitrification genes. Thus, NtrYX joins the increasing number of genetic regulators that contribute to the metabolic versatility required for the virulence of Brucella strains in their mammalian hosts.
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Affiliation(s)
- R Martin Roop
- Department of Microbiology and Immunology, Brody School of Medicine, East Carolina University, Greenville, NC 27834, USA.
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