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Chite Liu - One of the best experts on this subject based on the ideXlab platform.
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functional exploration of the bacterial type vi secretion system in mutualism Azorhizobium caulinodans ors571 sesbania rostrata as a research model
Molecular Plant-microbe Interactions, 2018Co-Authors: Hsiaohan Lin, Hsiaolin Chien, Chite Liu, Hsinmei Huang, Erhmin LaiAbstract:The bacterial type VI secretion system (T6SS) has been considered the armed force of bacteria because it can deliver toxin effectors to prokaryotic or eukaryotic cells for survival and fitness. Although many legume symbiotic rhizobacteria encode T6SS in their genome, the biological function of T6SS in these bacteria is still unclear. To elucidate this issue, we used Azorhizobium caulinodans ORS571 and its symbiotic host Sesbania rostrata as our research model. By using T6SS gene deletion mutants, we found that T6SS provides A. caulinodans with better symbiotic competitiveness when coinfected with a T6SS-lacking strain, as demonstrated by two independent T6SS-deficient mutants. Meanwhile, the symbiotic effectiveness was not affected by T6SS because the nodule phenotype, nodule size, and nodule nitrogen-fixation ability did not differ between the T6SS mutants and the wild type when infected alone. Our data also suggest that under several lab culture conditions tested, A. caulinodans showed no T6SS-dependent interbacterial competition activity. Therefore, instead of being an antihost or antibacterial weapon of the bacterium, the T6SS in A. caulinodans ORS571 seems to participate specifically in symbiosis by increasing its symbiotic competitiveness.
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comparative genome wide transcriptional profiling of Azorhizobium caulinodans ors571 grown under free living and symbiotic conditions
Applied and Environmental Microbiology, 2009Co-Authors: Shuhei Tsukada, Toshihiro Aono, Chite Liu, Kyung-bum Lee, Noriko Akiba, Hiroki Toyazaki, Hiroshi OyaizuAbstract:The whole-genome sequence of the endosymbiotic bacterium Azorhizobium caulinodans ORS571, which forms nitrogen-fixing nodules on the stems and roots of Sesbania rostrata, was recently determined. The sizes of the genome and symbiosis island are 5.4 Mb and 86.7 kb, respectively, and these sizes are the smallest among the sequenced rhizobia. In the present study, a whole-genome microarray of A. caulinodans was constructed, and transcriptomic analyses were performed on free-living cells grown in rich and minimal media and in bacteroids isolated from stem nodules. Transcriptional profiling showed that the genes involved in sulfur uptake and metabolism, acetone metabolism, and the biosynthesis of exopolysaccharide were highly expressed in bacteroids compared to the expression levels in free-living cells. Some mutants having Tn5 transposons within these genes with increased expression were obtained as nodule-deficient mutants in our previous study. A transcriptomic analysis was also performed on free-living cells grown in minimal medium supplemented with a flavonoid, naringenin, which is one of the most efficient inducers of A. caulinodans nod genes. Only 18 genes exhibited increased expression by the addition of naringenin, suggesting that the regulatory mechanism responding to the flavonoid could be simple in A. caulinodans. The combination of our genome-wide transcriptional profiling and our previous genome-wide mutagenesis study has revealed new aspects of nodule formation and maintenance.
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an outer membrane autotransporter aoaa of Azorhizobium caulinodans is required for sustaining high n2 fixing activity of stem nodules
Fems Microbiology Letters, 2008Co-Authors: Tadahiro Suzuki, Toshihiro Aono, Chite Liu, Shino Suzuki, Taichiro Iki, Keisuke Yokota, Hiroshi OyaizuAbstract:In this study, we investigated the function of a putative high-molecular-weight outer membrane protein, azorhizobial outer membrane autotransporter A (AoaA), of Azorhizobium caulinodans ORS571. Sequence analysis revealed that AoaA was an autotransporter protein belonging to the type V protein secretion system. Azorhizobium caulinodans forms N2-fixing nodules on the stems and roots of Sesbania rostrata . The sizes of stem nodules formed by an aoaA mutant having transposon insertion within this ORF were as large as those in the wild-type strain, but the N2-fixing activity of the nodules by the aoaA mutant was lower than that of wild-type nodules. cDNA-amplified fragment length polymorphism and reverse transcriptase-PCR analysis revealed that the expressions of several pathogen-related genes of host plants were induced in the aoaA mutant nodules. Furthermore, exopolysaccharide production was defective in the aoaA mutant under free-living conditions. These results indicate that AoaA may have an important role in sustaining the symbiosis by suppressing plant defense responses. The exopolysaccharide production controlled by AoaA might mediate this suppression mechanism.
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The genome of the versatile nitrogen fixer Azorhizobium caulinodans ORS571
BMC Genomics, 2008Co-Authors: Kyung-bum Lee, Tadahiro Suzuki, Toshihiro Aono, Chite Liu, Shino Suzuki, Philippe De Backer, Takakazu Kaneko, Manabu Yamada, Satoshi Tabata, Doris M KupferAbstract:Background Biological nitrogen fixation is a prokaryotic process that plays an essential role in the global nitrogen cycle. Azorhizobium caulinodans ORS571 has the dual capacity to fix nitrogen both as free-living organism and in a symbiotic interaction with Sesbania rostrata . The host is a fast-growing, submergence-tolerant tropical legume on which A. caulinodans can efficiently induce nodule formation on the root system and on adventitious rootlets located on the stem. Results The 5.37-Mb genome consists of a single circular chromosome with an overall average GC of 67% and numerous islands with varying GC contents. Most nodulation functions as well as a putative type-IV secretion system are found in a distinct symbiosis region. The genome contains a plethora of regulatory and transporter genes and many functions possibly involved in contacting a host. It potentially encodes 4717 proteins of which 96.3% have homologs and 3.7% are unique for A. caulinodans . Phylogenetic analyses show that the diazotroph Xanthobacter autotrophicus is the closest relative among the sequenced genomes, but the synteny between both genomes is very poor. Conclusion The genome analysis reveals that A. caulinodans is a diazotroph that acquired the capacity to nodulate most probably through horizontal gene transfer of a complex symbiosis island. The genome contains numerous genes that reflect a strong adaptive and metabolic potential. These combined features and the availability of the annotated genome make A. caulinodans an attractive organism to explore symbiotic biological nitrogen fixation beyond leguminous plants.
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the genome of the versatile nitrogen fixer Azorhizobium caulinodans ors571
BMC Genomics, 2008Co-Authors: Tadahiro Suzuki, Toshihiro Aono, Chite Liu, Shino Suzuki, Kyung-bum Lee, Philippe De Backer, Takakazu Kaneko, Manabu YamadaAbstract:Biological nitrogen fixation is a prokaryotic process that plays an essential role in the global nitrogen cycle. Azorhizobium caulinodans ORS571 has the dual capacity to fix nitrogen both as free-living organism and in a symbiotic interaction with Sesbania rostrata. The host is a fast-growing, submergence-tolerant tropical legume on which A. caulinodans can efficiently induce nodule formation on the root system and on adventitious rootlets located on the stem. The 5.37-Mb genome consists of a single circular chromosome with an overall average GC of 67% and numerous islands with varying GC contents. Most nodulation functions as well as a putative type-IV secretion system are found in a distinct symbiosis region. The genome contains a plethora of regulatory and transporter genes and many functions possibly involved in contacting a host. It potentially encodes 4717 proteins of which 96.3% have homologs and 3.7% are unique for A. caulinodans. Phylogenetic analyses show that the diazotroph Xanthobacter autotrophicus is the closest relative among the sequenced genomes, but the synteny between both genomes is very poor. The genome analysis reveals that A. caulinodans is a diazotroph that acquired the capacity to nodulate most probably through horizontal gene transfer of a complex symbiosis island. The genome contains numerous genes that reflect a strong adaptive and metabolic potential. These combined features and the availability of the annotated genome make A. caulinodans an attractive organism to explore symbiotic biological nitrogen fixation beyond leguminous plants.
Claudine Elmerich - One of the best experts on this subject based on the ideXlab platform.
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a chemotaxis like pathway of Azorhizobium caulinodans controls flagella driven motility which regulates biofilm formation exopolysaccharide biosynthesis and competitive nodulation
Molecular Plant-microbe Interactions, 2018Co-Authors: Wei Liu, Gladys Alexandre, Zhenpeng Zhang, Yu Sun, Xiaolin Liu, Xiaoxiao Dang, Rimin Shen, Fu Sui, Claudine ElmerichAbstract:The genome of the Azorhizobium caulinodans ORS571 contains a unique chemotaxis gene cluster (che) including five chemotaxis genes: cheA, cheW, cheY1, cheB, and cheR. Analysis of the role of the chemotaxis cluster of A. caulinodans using deletion mutant strains revealed that CheA or the Che signaling pathway controls chemotaxis behavior and flagella-driven motility and plays important roles in formation of biofilms and production of extracellular polysaccharides (EPS). Furthermore, the deletion mutants (ΔcheA and ΔcheA-R) were defective in competitive adsorption and colonization on the root surface of host plants. In addition, a functional CheA or Che pathway promoted competitive nodulation on roots and stems. Interestingly, a nonflagellated mutant, ΔfliM, displayed a phenotype highly similar to that of the ΔcheA or ΔcheA-R mutant strains. These findings suggest that through controlling flagella-driven motility behavior, the chemotaxis signaling pathway in A. caulinodans coordinates biofilm formation, EPS, and competitive colonization and nodulation.
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A cheZ-Like Gene in Azorhizobium caulinodans Is a Key Gene in the Control of Chemotaxis and Colonization of the Host Plant.
Applied and environmental microbiology, 2018Co-Authors: Xiaolin Liu, Claudine Elmerich, Yu Sun, Wei Liu, Chunlei Xia, Zhihong XieAbstract:ABSTRACT Chemotaxis can provide bacteria with competitive advantages for survival in complex environments. The CheZ chemotaxis protein is a phosphatase, affecting the flagellar motor in Escherichia coli by dephosphorylating the response regulator phosphorylated CheY protein (CheY∼P) responsible for clockwise rotation. A cheZ gene has been found in Azorhizobium caulinodans ORS571, in contrast to other rhizobial species studied so far. The CheZ protein in strain ORS571 has a conserved motif similar to that corresponding to the phosphatase active site in E. coli. The construction of a cheZ deletion mutant strain and of cheZ mutant strains carrying a mutation in residues of the putative phosphatase active site showed that strain ORS571 participates in chemotaxis and motility, causing a hyperreversal behavior. In addition, the properties of the cheZ deletion mutant revealed that ORS571 CheZ is involved in other physiological processes, since it displayed increased flocculation, biofilm formation, exopolysaccharide (EPS) production, and host root colonization. In particular, it was observed that the expression of several exp genes, involved in EPS synthesis, was upregulated in the cheZ mutant compared to that in the wild type, suggesting that CheZ negatively controls exp gene expression through an unknown mechanism. It is proposed that CheZ influences the Azorhizobium-plant association by negatively regulating early colonization via the regulation of EPS production. This report established that CheZ in A. caulinodans plays roles in chemotaxis and the symbiotic association with the host plant. IMPORTANCE Chemotaxis allows bacteria to swim toward plant roots and is beneficial to the establishment of various plant-microbe associations. The level of CheY phosphorylation (CheY∼P) is central to the chemotaxis signal transduction. The mechanism of the signal termination of CheY∼P remains poorly characterized among Alphaproteobacteria, except for Sinorhizobium meliloti, which does not contain CheZ but which controls CheY∼P dephosphorylation through a phosphate sink mechanism. Azorhizobium caulinodans ORS571, a microsymbiont of Sesbania rostrata, has an orphan cheZ gene besides two cheY genes similar to those in S. meliloti. In addition to controlling the chemotaxis response, the CheZ-like protein in strain ORS571 is playing a role by decreasing bacterial adhesion to the host plant, in contrast to the general situation where chemotaxis-associated proteins promote adhesion. In this study, we identified a CheZ-like protein among Alphaproteobacteria functioning in chemotaxis and the A. caulinodans-S. rostrata symbiosis.
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a chemotaxis receptor modulates nodulation during the Azorhizobium caulinodans sesbania rostrata symbiosis
Applied and Environmental Microbiology, 2016Co-Authors: Nan Jiang, Gladys Alexandre, Hailong Wu, Zhenhai Zhang, Yan Li, Claudine ElmerichAbstract:Azorhizobium caulinodans ORS571 is a free-living nitrogen-fixing bacterium which can induce nitrogen-fixing nodules both on the root and the stem of its legume host Sesbania rostrata. This bacterium, which is an obligate aerobe that moves by means of a polar flagellum, possesses a single chemotaxis signal transduction pathway. The objective of this work was to examine the role that chemotaxis and aerotaxis play in the lifestyle of the bacterium in free-living and symbiotic conditions. In bacterial chemotaxis, chemoreceptors sense environmental changes and transmit this information to the chemotactic machinery to guide motile bacteria to preferred niches. Here, we characterized a chemoreceptor of A. caulinodans containing an N-terminal PAS domain, named IcpB. IcpB is a soluble heme-binding protein that localized at the cell poles. An icpB mutant strain was impaired in sensing oxygen gradients and in chemotaxis response to organic acids. Compared to the wild-type strain, the icpB mutant strain was also affected in the production of extracellular polysaccharides and impaired in flocculation. When inoculated alone, the icpB mutant induced nodules on S. rostrata, but the nodules formed were smaller and had reduced N-2-fixing activity. The icpB mutant failed to nodulate its host when inoculated competitively with the wild-type strain. Together, the results identify chemotaxis and sensing of oxygen by IcpB as key regulators of the A. caulinodans-S. rostrata symbiosis.
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pii and glnk control ammonia assimilation and nitrogen fixation in Azorhizobium caulinodans
1999Co-Authors: N Michelreydellet, Claudine Elmerich, N Desnoues, P A KaminskiAbstract:Azorhizobium caulinodans fixes nitrogen both in the free-living state (Nif+) and in symbiosis (Fix+) with its host plant, Sesbania rostrata (Elmerich, et al., 1982). In the free-living state, all the fixed nitrogen is assimilated through the glutamine synthetase enzyme (GS) for the bacteria growth, suggesting a coordination between ammonia assimilation and nitrogen fixation.
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poly beta hydroxybutyrate turnover in Azorhizobium caulinodans is required for growth and affects nifa expression
Journal of Bacteriology, 1998Co-Authors: K Mandon, Claudine Elmerich, N Michelreydellet, P A Kaminski, Sergio Encarnacion, A Leija, M G Cevallos, J MoraAbstract:Azorhizobium caulinodans is able to fix nitrogen in the free-living state and in symbiosis with the tropical legume Sesbania rostrata. The bacteria accumulate poly-beta-hydroxybutyrate (PHB) under both conditions. The structural gene for PHB synthase, phbC, was inactivated by insertion of an interposon. The mutant strains obtained were devoid of PHB, impaired in their growth properties, totally devoid of nitrogenase activity ex planta (Nif-), and affected in nucleotide pools and induced Fix- nodules devoid of bacteria. The Nif- phenotype was the consequence of the lack of nifA transcription. Nitrogenase activity was partially restored to a phbC mutant by constitutive expression of the nifA gene. However, this constitutive nifA expression had no effect on the nucleotide content or on growth of the phbC mutant. It is suggested that PHB is required for maintaining the reducing power of the cell and therefore the bacterial growth. These observations also suggest a new control of nifA expression to adapt nitrogen fixation to the availability of carbon and reducing equivalents.
Robert A. Ludwig - One of the best experts on this subject based on the ideXlab platform.
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respiratory membrane endo hydrogenase activity in the microaerophile Azorhizobium caulinodans is bidirectional
PLOS ONE, 2012Co-Authors: Brittany N Sprecher, Margo E Gittings, Robert A. LudwigAbstract:Background The microaerophilic bacterium Azorhizobium caulinodans, when fixing N2 both in pure cultures held at 20 µM dissolved O2 tension and as endosymbiont of Sesbania rostrata legume nodules, employs a novel, respiratory-membrane endo-hydrogenase to oxidize and recycle endogenous H2 produced by soluble Mo-dinitrogenase activity at the expense of O2.
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Azorhizobium caulinodans strains.
2012Co-Authors: Brittany N Sprecher, Margo E Gittings, Robert A. LudwigAbstract:Azorhizobium caulinodans strains.
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Respiratory Membrane endo-Hydrogenase Activity in the Microaerophile Azorhizobium caulinodans Is Bidirectional
2012Co-Authors: Brittany N Sprecher, Margo E Gittings, Robert A. LudwigAbstract:BackgroundThe microaerophilic bacterium Azorhizobium caulinodans, when fixing N2 both in pure cultures held at 20 µM dissolved O2 tension and as endosymbiont of Sesbania rostrata legume nodules, employs a novel, respiratory-membrane endo-hydrogenase to oxidize and recycle endogenous H2 produced by soluble Mo-dinitrogenase activity at the expense of O2. Methods and FindingsFrom a bioinformatic analysis, this endo-hydrogenase is a core (6 subunit) version of (14 subunit) NADH:ubiquinone oxidoreductase (respiratory complex I). In pure A. caulinodans liquid cultures, when O2 levels are lowered to
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Azorhizobium caulinodans electron transferring flavoprotein n electrochemically couples pyruvate dehydrogenase complex activity to n2 fixation
Microbiology, 2004Co-Authors: John D. Scott, Robert A. LudwigAbstract:Azorhizobium caulinodans thermolabile point mutants unable to fix N2 at 42 °C were isolated and mapped to three, unlinked loci; from complementation tests, several mutants were assigned to the fixABCX locus. Of these, two independent fixB mutants carried missense substitutions in the product electron-transferring flavoprotein N (ETFN) α-subunit. Both thermolabile missense variants Y238H and D229G mapped to the ETFN α interdomain linker. Unlinked thermostable suppressors of these two fixB missense mutants were identified and mapped to the lpdA gene, encoding dihydrolipoamide dehydrogenase (LpDH), immediately distal to the pdhABC genes, which collectively encode the pyruvate dehydrogenase (PDH) complex. These two suppressor alleles encoded LpDH NAD-binding domain missense mutants G187S and E210G. Crude cell extracts of these fixB lpdA double mutants showed 60–70 % of the wild-type PDH activity; neither fixB lpdA double mutant strain exhibited any growth phenotype at the restrictive or the permissive temperature. The genetic interaction between two combinations of lpdA and fixB missense alleles implies a physical interaction of their respective products, LpDH and ETFN. Presumably, this interaction electrochemically couples LpDH as the electron donor to ETFN as the electron acceptor, allowing PDH complex activity (pyruvate oxidation) to drive soluble electron transport via ETFN to N2, which acts as the terminal electron acceptor. If so, then, the A. caulinodans PDH complex activity sustains N2 fixation both as the driving force for oxidative phosphorylation and as the metabolic electron donor.
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Azorhizobium caulinodans pyruvate dehydrogenase activity is dispensable for aerobic but required for microaerobic growth
Microbiology, 2001Co-Authors: David C Pauling, Jerome P Lapointe, Carolyn M Paris, Robert A. LudwigAbstract:Azorhizobium caulinodans mutant 62004 carries a null allele of pdhB, encoding the E1β subunit of pyruvate dehydrogenase, which converts pyruvate to acetyl-CoA. This pdhB mutant completely lacks pyruvate oxidation activities yet grows aerobically on C4 dicarboxylates (succinate, L-malate) as sole energy source, albeit slowly, and displays pleiotropic growth defects consistent with physiological acetyl-CoA limitation. Temperature-sensitive (ts), conditional-lethal derivatives of the pdhB mutant lack (methyl)malonate semialdehyde dehydrogenase activity, which thus also allows L-malate conversion to acetyl-CoA. The pdhB mutant remains able to fix N2 in aerobic culture, but is unable to fix N2 in symbiosis with host Sesbania rostrata plants and cannot grow microaerobically. In culture, A. caulinodans wild-type can use acetate, β-D-hydroxybutyrate and nicotinate – all direct precursors of acetyl-CoA – as sole C and energy source for aerobic, but not microaerobic growth. Paradoxically, acetyl-CoA is thus a required intermediate for microaerobic oxidative energy transduction while not itself oxidized. Accordingly, A. caulinodans energy transduction under aerobic and microaerobic conditions is qualitatively different.
Zhihong Xie - One of the best experts on this subject based on the ideXlab platform.
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Azorhizobium caulinodans chemotaxis is controlled by an unusual phosphorelay network
Journal of Bacteriology, 2021Co-Authors: Emily N Kennedy, Zhihong Xie, Yanan Liu, Xiaolin Liu, Sarah A Barr, Luke R Vass, Robert B BourretAbstract:Azorhizobium caulinodans is a nitrogen-fixing bacterium that forms root nodules on its host legume, Sesbania rostrata. This agriculturally significant symbiotic relationship is important in lowland rice cultivation, and allows for nitrogen fixation under flood conditions. Chemotaxis plays an important role in bacterial colonization of the rhizosphere. Plant roots release chemical compounds that are sensed by bacteria, triggering chemotaxis along a concentration gradient toward the roots. This gives motile bacteria a significant competitive advantage during root surface colonization. Although plant-associated bacterial genomes often encode multiple chemotaxis systems, A. caulinodans appears to encode only one. The che cluster on the A. caulinodans genome contains cheA, cheW, cheY2, cheB, and cheR. Two other chemotaxis genes, cheY1 and cheZ, are located independently from the che operon. Both CheY1 and CheY2 are involved in chemotaxis, with CheY1 being the predominant signaling protein. A. caulinodans CheA contains an unusual set of C-terminal domains: a CheW-like/Receiver pair (termed W2-Rec), follows the more common single CheW-like domain. W2-Rec impacts both chemotaxis and CheA function. We found a preference for transfer of phosphoryl groups from CheA to CheY2, rather than to W2-Rec or CheY1, which appears to be involved in flagellar motor binding. Furthermore, we observed increased phosphoryl group stabilities on CheY1 compared to CheY2 or W2-Rec. Finally, CheZ enhanced dephosphorylation of CheY2 substantially more than CheY1, but had no effect on the dephosphorylation rate of W2-Rec. This network of phosphotransfer reactions highlights a previously uncharacterized scheme for regulation of chemotactic responses. IMPORTANCE Chemotaxis allows bacteria to move towards nutrients and away from toxins in their environment. Chemotactic movement provides a competitive advantage over non-specific motion. CheY is an essential mediator of the chemotactic response with phosphorylated and unphosphorylated forms of CheY differentially interacting with the flagellar motor to change swimming behavior. Previously established schemes of CheY dephosphorylation include action of a phosphatase and/or transfer of the phosphoryl group to another receiver domain that acts as a sink. Here, we propose A. caulinodans uses a concerted mechanism in which the Hpt domain of CheA, CheY2, and CheZ function together as a dual sink system to rapidly reset chemotactic signaling. To the best of our knowledge, this mechanism is unlike any that have previously been evaluated. Chemotaxis systems that utilize both receiver and Hpt domains as phosphate sinks likely occur in other bacterial species.
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Protein Residues and a Novel Motif Involved in the Cellular Localization of CheZ in Azorhizobium caulinodans ORS571.
Frontiers in microbiology, 2020Co-Authors: Xiaolin Liu, Yanan Liu, Xiaoyan Dong, Kevin S. Johnson, Zhihong XieAbstract:Chemotaxis is essential for the competitiveness of motile bacteria in complex and harsh environments. The localization of chemotactic proteins in the cell is critical for coordinating a maximal response to chemotactic signals. One chemotaxis protein with a well-defined subcellular localization is the phosphatase CheZ. CheZ localizes to cell poles by binding with CheA in Escherichia coli and other enteric bacteria, or binding with a poorly understood protein called ChePep in epsilon-Proteobacteria. In alpha-Proteobacteria, CheZ lacks CheA-binding sites, and its cellular localization remains unknown. We therefore determined the localization of CheZ in the alpha-Proteobacteria Azorhizobium caulinodans ORS571. A. caulinodans CheZ, also termed as CheZAC, was found to be located to cell poles independently of CheA, and we suspect that either the N-terminal helix or the four-helix bundle of CheZAC is sufficient to locate to cell poles. We also found a novel motif, AXXFQ, which is adjacent to the phosphatase active motif DXXXQ, which effects the monopolar localization of CheZAC. This novel motif consisting of AXXFQ is conserved in CheZ and widely distributed among Proteobacteria. Finally, we found that the substitution of phosphatase active site affects the polar localization of CheZAC. In total, this work characterized the localization pattern of CheZ containing a novel motif, and we mapped the regions of CheZAC that are critical for its polar localization.
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Azorhizobium caulinodans c-di-GMP phosphodiesterase Chp1 involved in motility, EPS production, and nodulation of the host plant.
Applied Microbiology and Biotechnology, 2020Co-Authors: Yu Sun, Yanan Liu, Xiaolin Liu, Xiaoxiao Dang, Xiaoyan Dong, Zhihong XieAbstract:Establishment of the rhizobia-legume symbiosis is usually accompanied by hydrogen peroxide (H2O2) production by the legume host at the site of infection, a process detrimental to rhizobia. In Azorhizobium caulinodans ORS571, deletion of chp1, a gene encoding c-di-GMP phosphodiesterase, led to increased resistance against H2O2 and to elevated nodulation efficiency on its legume host Sesbania rostrata. Three domains were identified in the Chp1: a PAS domain, a degenerate GGDEF domain, and an EAL domain. An in vitro enzymatic activity assay showed that the degenerate GGDEF domain of Chp1 did not have diguanylate cyclase activity. The phosphodiesterase activity of Chp1 was attributed to its EAL domain which could hydrolyse c-di-GMP into pGpG. The PAS domain functioned as a regulatory domain by sensing oxygen. Deletion of Chp1 resulted in increased intracellular c-di-GMP level, decreased motility, increased aggregation, and increased EPS (extracellular polysaccharide) production. H2O2-sensitivity assay showed that increased EPS production could provide ORS571 with resistance against H2O2. Thus, the elevated nodulation efficiency of the ∆chp1 mutant could be correlated with a protective role of EPS in the nodulation process. These data suggest that c-di-GMP may modulate the A. caulinodans-S. rostrata nodulation process by regulating the production of EPS which could protect rhizobia against H2O2.
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prediction and functional analysis of ggdef eal domain containing proteins in Azorhizobium caulinodans ors571
2019Co-Authors: Yu Sun, Zhihong Xie, Wei Liu, Hongen GuoAbstract:Objectivec-di-GMP, an important second messenger regulating multiple functions of bacteria, is generally synthesized and hydrolysed by proteins containing GGDEF or EAL domain. In this study, we analyzed the genome-wide GGDEF/EAL domain-containing proteins of Azorhizobium caulinodans ORS571, and selected three GGDEF-EAL composite proteins (AZC_3085, AZC_3226 and AZC_4658) for functional analysis. MethodsSMART and CLUSTALW were used for prediction and multi-alignment of GGDEF/EAL domain-containing proteins. Mutants were constructed by homologous recombination. Phenotypes including cell motility, exopolysaccharide (EPS) production, biofilm formation and nodulation with legume host were investigated. ResultsThere were 37 GGDEF/EAL domain-containing proteins in A. caulinodans ORS571. Mutant △4658 showed deficiency in cell motility, while its EPS production and biofilm formation were higher than that of wild type. Mutant △4658 showed stronger competitiveness than wild type in competitive nodulation assay. The loss of AZC_4658 led to the increase of intracellular c-di-GMP level. Mutants △3085 and △3226 did not show obvious difference in comparison with wild type. ConclusionThe vast number of GGDEF/EAL domain-containing proteins suggested that c-di-GMP may play an important role in signal transduction of ORS571. The GGDEF-EAL composite protein AZC_4658 was involved in cell motility, EPS production, biofilm formation and nodulation of A. caulinodans ORS571.
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A cheZ-Like Gene in Azorhizobium caulinodans Is a Key Gene in the Control of Chemotaxis and Colonization of the Host Plant.
Applied and environmental microbiology, 2018Co-Authors: Xiaolin Liu, Claudine Elmerich, Yu Sun, Wei Liu, Chunlei Xia, Zhihong XieAbstract:ABSTRACT Chemotaxis can provide bacteria with competitive advantages for survival in complex environments. The CheZ chemotaxis protein is a phosphatase, affecting the flagellar motor in Escherichia coli by dephosphorylating the response regulator phosphorylated CheY protein (CheY∼P) responsible for clockwise rotation. A cheZ gene has been found in Azorhizobium caulinodans ORS571, in contrast to other rhizobial species studied so far. The CheZ protein in strain ORS571 has a conserved motif similar to that corresponding to the phosphatase active site in E. coli. The construction of a cheZ deletion mutant strain and of cheZ mutant strains carrying a mutation in residues of the putative phosphatase active site showed that strain ORS571 participates in chemotaxis and motility, causing a hyperreversal behavior. In addition, the properties of the cheZ deletion mutant revealed that ORS571 CheZ is involved in other physiological processes, since it displayed increased flocculation, biofilm formation, exopolysaccharide (EPS) production, and host root colonization. In particular, it was observed that the expression of several exp genes, involved in EPS synthesis, was upregulated in the cheZ mutant compared to that in the wild type, suggesting that CheZ negatively controls exp gene expression through an unknown mechanism. It is proposed that CheZ influences the Azorhizobium-plant association by negatively regulating early colonization via the regulation of EPS production. This report established that CheZ in A. caulinodans plays roles in chemotaxis and the symbiotic association with the host plant. IMPORTANCE Chemotaxis allows bacteria to swim toward plant roots and is beneficial to the establishment of various plant-microbe associations. The level of CheY phosphorylation (CheY∼P) is central to the chemotaxis signal transduction. The mechanism of the signal termination of CheY∼P remains poorly characterized among Alphaproteobacteria, except for Sinorhizobium meliloti, which does not contain CheZ but which controls CheY∼P dephosphorylation through a phosphate sink mechanism. Azorhizobium caulinodans ORS571, a microsymbiont of Sesbania rostrata, has an orphan cheZ gene besides two cheY genes similar to those in S. meliloti. In addition to controlling the chemotaxis response, the CheZ-like protein in strain ORS571 is playing a role by decreasing bacterial adhesion to the host plant, in contrast to the general situation where chemotaxis-associated proteins promote adhesion. In this study, we identified a CheZ-like protein among Alphaproteobacteria functioning in chemotaxis and the A. caulinodans-S. rostrata symbiosis.
Yu Sun - One of the best experts on this subject based on the ideXlab platform.
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Azorhizobium caulinodans c-di-GMP phosphodiesterase Chp1 involved in motility, EPS production, and nodulation of the host plant
'Springer Science and Business Media LLC', 2020Co-Authors: Yu Sun, Liu Yanan, Liu Xiaolin, Dang Xiaoxiao, Dong Xiaoyan, Xie ZhihongAbstract:Establishment of the rhizobia-legume symbiosis is usually accompanied by hydrogen peroxide (H2O2) production by the legume host at the site of infection, a process detrimental to rhizobia. In Azorhizobium caulinodans ORS571, deletion of chp1, a gene encoding c-di-GMP phosphodiesterase, led to increased resistance against H2O2 and to elevated nodulation efficiency on its legume host Sesbania rostrata. Three domains were identified in the Chp1: a PAS domain, a degenerate GGDEF domain, and an EAL domain. An in vitro enzymatic activity assay showed that the degenerate GGDEF domain of Chp1 did not have diguanylate cyclase activity. The phosphodiesterase activity of Chp1 was attributed to its EAL domain which could hydrolyse c-di-GMP into pGpG. The PAS domain functioned as a regulatory domain by sensing oxygen. Deletion of Chp1 resulted in increased intracellular c-di-GMP level, decreased motility, increased aggregation, and increased EPS (extracellular polysaccharide) production. H2O2-sensitivity assay showed that increased EPS production could provide ORS571 with resistance against H2O2. Thus, the elevated nodulation efficiency of the increment chp1 mutant could be correlated with a protective role of EPS in the nodulation process. These data suggest that c-di-GMP may modulate the A. caulinodans-S. rostrata nodulation process by regulating the production of EPS which could protect rhizobia against H2O2
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Azorhizobium caulinodans c-di-GMP phosphodiesterase Chp1 involved in motility, EPS production, and nodulation of the host plant.
Applied Microbiology and Biotechnology, 2020Co-Authors: Yu Sun, Yanan Liu, Xiaolin Liu, Xiaoxiao Dang, Xiaoyan Dong, Zhihong XieAbstract:Establishment of the rhizobia-legume symbiosis is usually accompanied by hydrogen peroxide (H2O2) production by the legume host at the site of infection, a process detrimental to rhizobia. In Azorhizobium caulinodans ORS571, deletion of chp1, a gene encoding c-di-GMP phosphodiesterase, led to increased resistance against H2O2 and to elevated nodulation efficiency on its legume host Sesbania rostrata. Three domains were identified in the Chp1: a PAS domain, a degenerate GGDEF domain, and an EAL domain. An in vitro enzymatic activity assay showed that the degenerate GGDEF domain of Chp1 did not have diguanylate cyclase activity. The phosphodiesterase activity of Chp1 was attributed to its EAL domain which could hydrolyse c-di-GMP into pGpG. The PAS domain functioned as a regulatory domain by sensing oxygen. Deletion of Chp1 resulted in increased intracellular c-di-GMP level, decreased motility, increased aggregation, and increased EPS (extracellular polysaccharide) production. H2O2-sensitivity assay showed that increased EPS production could provide ORS571 with resistance against H2O2. Thus, the elevated nodulation efficiency of the ∆chp1 mutant could be correlated with a protective role of EPS in the nodulation process. These data suggest that c-di-GMP may modulate the A. caulinodans-S. rostrata nodulation process by regulating the production of EPS which could protect rhizobia against H2O2.
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prediction and functional analysis of ggdef eal domain containing proteins in Azorhizobium caulinodans ors571
2019Co-Authors: Yu Sun, Zhihong Xie, Wei Liu, Hongen GuoAbstract:Objectivec-di-GMP, an important second messenger regulating multiple functions of bacteria, is generally synthesized and hydrolysed by proteins containing GGDEF or EAL domain. In this study, we analyzed the genome-wide GGDEF/EAL domain-containing proteins of Azorhizobium caulinodans ORS571, and selected three GGDEF-EAL composite proteins (AZC_3085, AZC_3226 and AZC_4658) for functional analysis. MethodsSMART and CLUSTALW were used for prediction and multi-alignment of GGDEF/EAL domain-containing proteins. Mutants were constructed by homologous recombination. Phenotypes including cell motility, exopolysaccharide (EPS) production, biofilm formation and nodulation with legume host were investigated. ResultsThere were 37 GGDEF/EAL domain-containing proteins in A. caulinodans ORS571. Mutant △4658 showed deficiency in cell motility, while its EPS production and biofilm formation were higher than that of wild type. Mutant △4658 showed stronger competitiveness than wild type in competitive nodulation assay. The loss of AZC_4658 led to the increase of intracellular c-di-GMP level. Mutants △3085 and △3226 did not show obvious difference in comparison with wild type. ConclusionThe vast number of GGDEF/EAL domain-containing proteins suggested that c-di-GMP may play an important role in signal transduction of ORS571. The GGDEF-EAL composite protein AZC_4658 was involved in cell motility, EPS production, biofilm formation and nodulation of A. caulinodans ORS571.
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a chemotaxis like pathway of Azorhizobium caulinodans controls flagella driven motility which regulates biofilm formation exopolysaccharide biosynthesis and competitive nodulation
Molecular Plant-microbe Interactions, 2018Co-Authors: Wei Liu, Gladys Alexandre, Zhenpeng Zhang, Yu Sun, Xiaolin Liu, Xiaoxiao Dang, Rimin Shen, Fu Sui, Claudine ElmerichAbstract:The genome of the Azorhizobium caulinodans ORS571 contains a unique chemotaxis gene cluster (che) including five chemotaxis genes: cheA, cheW, cheY1, cheB, and cheR. Analysis of the role of the chemotaxis cluster of A. caulinodans using deletion mutant strains revealed that CheA or the Che signaling pathway controls chemotaxis behavior and flagella-driven motility and plays important roles in formation of biofilms and production of extracellular polysaccharides (EPS). Furthermore, the deletion mutants (ΔcheA and ΔcheA-R) were defective in competitive adsorption and colonization on the root surface of host plants. In addition, a functional CheA or Che pathway promoted competitive nodulation on roots and stems. Interestingly, a nonflagellated mutant, ΔfliM, displayed a phenotype highly similar to that of the ΔcheA or ΔcheA-R mutant strains. These findings suggest that through controlling flagella-driven motility behavior, the chemotaxis signaling pathway in A. caulinodans coordinates biofilm formation, EPS, and competitive colonization and nodulation.
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A cheZ-Like Gene in Azorhizobium caulinodans Is a Key Gene in the Control of Chemotaxis and Colonization of the Host Plant.
Applied and environmental microbiology, 2018Co-Authors: Xiaolin Liu, Claudine Elmerich, Yu Sun, Wei Liu, Chunlei Xia, Zhihong XieAbstract:ABSTRACT Chemotaxis can provide bacteria with competitive advantages for survival in complex environments. The CheZ chemotaxis protein is a phosphatase, affecting the flagellar motor in Escherichia coli by dephosphorylating the response regulator phosphorylated CheY protein (CheY∼P) responsible for clockwise rotation. A cheZ gene has been found in Azorhizobium caulinodans ORS571, in contrast to other rhizobial species studied so far. The CheZ protein in strain ORS571 has a conserved motif similar to that corresponding to the phosphatase active site in E. coli. The construction of a cheZ deletion mutant strain and of cheZ mutant strains carrying a mutation in residues of the putative phosphatase active site showed that strain ORS571 participates in chemotaxis and motility, causing a hyperreversal behavior. In addition, the properties of the cheZ deletion mutant revealed that ORS571 CheZ is involved in other physiological processes, since it displayed increased flocculation, biofilm formation, exopolysaccharide (EPS) production, and host root colonization. In particular, it was observed that the expression of several exp genes, involved in EPS synthesis, was upregulated in the cheZ mutant compared to that in the wild type, suggesting that CheZ negatively controls exp gene expression through an unknown mechanism. It is proposed that CheZ influences the Azorhizobium-plant association by negatively regulating early colonization via the regulation of EPS production. This report established that CheZ in A. caulinodans plays roles in chemotaxis and the symbiotic association with the host plant. IMPORTANCE Chemotaxis allows bacteria to swim toward plant roots and is beneficial to the establishment of various plant-microbe associations. The level of CheY phosphorylation (CheY∼P) is central to the chemotaxis signal transduction. The mechanism of the signal termination of CheY∼P remains poorly characterized among Alphaproteobacteria, except for Sinorhizobium meliloti, which does not contain CheZ but which controls CheY∼P dephosphorylation through a phosphate sink mechanism. Azorhizobium caulinodans ORS571, a microsymbiont of Sesbania rostrata, has an orphan cheZ gene besides two cheY genes similar to those in S. meliloti. In addition to controlling the chemotaxis response, the CheZ-like protein in strain ORS571 is playing a role by decreasing bacterial adhesion to the host plant, in contrast to the general situation where chemotaxis-associated proteins promote adhesion. In this study, we identified a CheZ-like protein among Alphaproteobacteria functioning in chemotaxis and the A. caulinodans-S. rostrata symbiosis.
