title: The NtrY/NtrX System of Sinorhizobium meliloti GR4 Regulates Motility, EPS I Production, and Nitrogen Metabolism but Is Dispensable for Symbiotic Nitrogen Fixation.
abstract: Sinorhizobium meliloti can translocate over surfaces. However, little is known about the regulatory mechanisms that control this trait and its relevance for establishing symbiosis with alfalfa plants. To gain insights into this field, we isolated Tn5 mutants of S. meliloti GR4 with impaired surface motility. In mutant strain GRS577, the transposon interrupted the ntrY gene encoding the sensor kinase of the NtrY/NtrX two-component regulatory system. GRS577 is impaired in flagella synthesis and overproduces succinoglycan, which is responsible for increased biofilm formation. The mutant also shows altered cell morphology and higher susceptibility to salt stress. GRS577 induces nitrogen-fixing nodules in alfalfa but exhibits decreased competitive nodulation. Complementation experiments indicate that both ntrY and ntrX account for all the phenotypes displayed by the ntrY::Tn5 mutant. Ectopic overexpression of VisNR, the motility master regulator, was sufficient to rescue motility and competitive nodulation of the transposant. A transcriptome profiling of GRS577 confirmed differential expression of exo and flagellar genes, and led to the demonstration that NtrY/NtrX allows for optimal expression of denitrification and nifA genes under microoxic conditions in response to nitrogen compounds. This study extends our knowledge of the complex role played by NtrY/NtrX in S. meliloti.
authors.affiliation: Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas (CSIC), Profesor Albareda 1, 18008 Granada, Spain.
authors.forename: Nieves
authors.initials: N
authors.lastname: Calatrava-Morales
authors.affiliation: Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas (CSIC), Profesor Albareda 1, 18008 Granada, Spain.
authors.forename: Joaquina
authors.initials: J
authors.lastname: Nogales
authors.affiliation: Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas (CSIC), Profesor Albareda 1, 18008 Granada, Spain.
authors.forename: Kinia
authors.initials: K
authors.lastname: Ameztoy
authors.affiliation: Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas (CSIC), Profesor Albareda 1, 18008 Granada, Spain.
authors.forename: Bart
authors.initials: B
authors.lastname: van Steenbergen
authors.affiliation: Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas (CSIC), Profesor Albareda 1, 18008 Granada, Spain.
authors.forename: María J
authors.identifier: 0000-0003-2045-7238
authors.initials: MJ
authors.lastname: Soto
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D018441:Biofilms; D004251:DNA Transposable Elements / Q000235:genetics; D005407:Flagella / Q000235:genetics / Q000502:physiology; D020869:Gene Expression Profiling / Q000379:methods; D015964:Gene Expression Regulation, Bacterial; D054884:Host-Pathogen Interactions; D000455:Medicago sativa / Q000382:microbiology; D016254:Mutagenesis, Insertional; D009584:Nitrogen / Q000378:metabolism*; D009586:Nitrogen Fixation / Q000235:genetics; D018517:Plant Roots / Q000382:microbiology; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis*; D016962:Sinorhizobium meliloti / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D013559:Symbiosis
chemical_list: D001426:Bacterial Proteins; D004251:DNA Transposable Elements; C083492:EPSI polysaccharide; D011135:Polysaccharides, Bacterial; D009584:Nitrogen