Exopolysaccharide is detrimental for the symbiotic performance of Sinorhizobium fredii HH103 mutants with a truncated lipopolysaccharide core.

The nitrogen-fixing rhizobia-legume symbiosis relies on a complex interchange of molecular signals between the two partners during the whole interaction. On the bacterial side, different surface polysaccharides, such as lipopolysaccharide (LPS) and exopolysaccharide (EPS), might play important roles for the success of the interaction. In a previous work we studied two Sinorhizobium fredii HH103 mutants affected in the rkpK and lpsL genes, which are responsible for the production of glucuronic acid and galacturonic acid, respectively.

Methods for Studying Swimming and Surface Motilities in Rhizobia.

Rhizobia are soil proteobacteria able to establish a nitrogen-fixing interaction with legumes. In this interaction, rhizobia must colonize legume roots, infect them, and become hosted inside new organs formed by the plants and called nodules. Rhizobial motility, not being essential for symbiosis, might affect the degree of success of the interaction with legumes.

A complex regulatory network governs the expression of symbiotic genes in HH103.

Introduction: The establishment of the rhizobium-legume nitrogen-fixing symbiosis relies on the interchange of molecular signals between the two symbionts. We have previously studied by RNA-seq the effect of the symbiotic regulators NodD1, SyrM, and TtsI on the expression of the symbiotic genes (the regulon) of HH103 upon treatment with the isoflavone genistein. In this work we have further investigated this regulatory network by incorporating new RNA-seq data of HH103 mutants in two other regulatory genes, and .

Surface Motility Regulation of HH103 by Plant Flavonoids and the NodD1, TtsI, NolR, and MucR1 Symbiotic Bacterial Regulators.

Bacteria can spread on surfaces to colonize new environments and access more resources. Rhizobia, a group of α- and β-, establish nitrogen-fixing symbioses with legumes that rely on a complex signal interchange between the partners. Flavonoids exuded by plant roots and the bacterial transcriptional activator NodD control the transcription of different rhizobial genes (the so-called regulon) and, together with additional bacterial regulatory proteins (such as TtsI, MucR or NolR), influence the production of different rhizobial molecular signals.

The Sinorhizobium fredii HH103 type III secretion system effector NopC blocks nodulation with Lotus japonicus Gifu.

The broad-host-range bacterium Sinorhizobium fredii HH103 cannot nodulate the model legume Lotus japonicus Gifu. This bacterium possesses a type III secretion system (T3SS), a specialized secretion apparatus used to deliver effector proteins (T3Es) into the host cell cytosol to alter host signaling and/or suppress host defence responses to promote infection. However, some of these T3Es are recognized by specific plant receptors and hence trigger a strong defence response to block infection.

Structure of the unusual HH103 lipopolysaccharide and its role in symbiosis.

Rhizobia are soil bacteria that form important symbiotic associations with legumes, and rhizobial surface polysaccharides, such as K-antigen polysaccharide (KPS) and lipopolysaccharide (LPS), might be important for symbiosis. Previously, we obtained a mutant of HH103, , that does not produce KPS, a homopolysaccharide of a pseudaminic acid derivative, but whose LPS electrophoretic profile was indistinguishable from that of the WT strain. We also previously demonstrated that the HH103 operon is responsible for 5-acetamido-3,5,7,9-tetradeoxy-7-(3-hydroxybutyramido)-l--l--nonulosonic acid [Pse5NAc7(3OHBu)] production and is involved in HH103 KPS and LPS biosynthesis and that an HH103 mutant cannot produce KPS and displays an altered LPS structure.

Diversity of Bacteriophages in the Rhizosphere of : Myoviruses, Filamentous and N4-Like Podovirus.

Using different strains as hosts, we isolated eight new virulent phages from the rhizosphere of the coastal legume . Half of the isolated phages showed a very narrow host range while the other half exhibited a wider host range within the strains tested. Electron microscopy studies showed that phages M_ort18, M_sf1.

Deciphering the Symbiotic Significance of Quorum Sensing Systems of HH103.

Quorum sensing (QS) is a bacterial cell-to-cell signaling mechanism that collectively regulates and synchronizes behaviors by means of small diffusible chemical molecules. In rhizobia, QS systems usually relies on the synthesis and detection of -acyl-homoserine lactones (AHLs). In the model bacterium functions regulated by the QS systems TraI-TraR and SinI-SinR(-ExpR) include plasmid transfer, production of surface polysaccharides, motility, growth rate and nodulation.

Sinorhizobium fredii HH103 nolR and nodD2 mutants gain capacity for infection thread invasion of Lotus japonicus Gifu and Lotus burttii.

Sinorhizobium fredii HH103 Rif , a broad-host-range rhizobial strain, forms ineffective nodules with Lotus japonicus but induces nitrogen-fixing nodules in Lotus burttii roots that are infected by intercellular entry. Here we show that HH103 Rif nolR or nodD2 mutants gain the ability to induce infection thread formation and to form nitrogen-fixing nodules in L. japonicus Gifu.

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

Members of 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 and , mutations in do not impair symbiotic nitrogen fixation.

The Sinorhizobium fredii HH103 MucR1 Global Regulator Is Connected With the nod Regulon and Is Required for Efficient Symbiosis With Lotus burttii and Glycine max cv. Williams.

Sinorhizobium fredii HH103 is a rhizobial strain showing a broad host range of nodulation. In addition to the induction of bacterial nodulation genes, transition from a free-living to a symbiotic state requires complex genetic expression changes with the participation of global regulators. We have analyzed the role of the zinc-finger transcriptional regulator MucR1 from S.

Rhizobial strains isolated from nodules of Medicago marina in southwest Spain are abiotic-stress tolerant and symbiotically diverse.

The isolation and characterisation of nitrogen-fixing root nodule bacteria from Medicago marina, a tolerant legume species, were studied in two areas from southwest Spain. A total of 30 out of 82 isolates with distinct ERIC-PCR fingerprints were analysed on the basis of molecular (PCR-RFLP of the 16S-23S rDNA intergenic spacer region (IGS) with two endonucleases, analysis of the 16S rDNA and symbiotic nodC gene sequences, plasmid profiles and SDS-PAGE of LPS, including the partial sequence of the housekeeping gene glnII and the symbiotic gene nodA of some representatives), physiological (utilisation of sole carbon sources, tolerance to antibiotics, NaCl, heavy metals, temperature and pH) and symbiotic parameters (efficacy on M. marina, M.

Sphingopyxis italica sp. nov., isolated from Roman catacombs.

A Gram-stain-negative, aerobic, motile, rod-shaped bacterium, strain SC13E-S71(T), was isolated from tuff, volcanic rock, where the Roman catacombs of Saint Callixtus in Rome, Italy, was excavated. Analysis of 16S rRNA gene sequences revealed that strain SC13E-S71(T) belongs to the genus Sphingopyxis, and that it shows the greatest sequence similarity with Sphingopyxis chilensis DSM 14889(T) (98.72 %), Sphingopyxis taejonensis DSM 15583(T) (98.

Nocardioides albertanoniae sp. nov., isolated from Roman catacombs.

A Gram-reaction-positive, aerobic, non-spore-forming, rod- or coccoid-shaped, strain, CD40127(T), was isolated from a green biofilm covering the wall of the Domitilla Catacombs in Rome, Italy. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain CD40127(T) belongs to the genus Nocardioides, closely related to Nocardioides luteus DSM 43366(T) and Nocardioides albus DSM 43109(T) with 98.86 % and 98.

Rubrobacter bracarensis sp. nov., a novel member of the genus Rubrobacter isolated from a biodeteriorated monument.

Three actinobacteria strains isolated from a green biofilm covering the biodeteriorated interior walls of Vilar de Frades Church (Portugal) were studied using a polyphasic approach. The three strains were aerobic, non-spore forming and Gram-positive. Phylogenetically, the most closely related described species was Rubrobacter radiotolerans (94.