scholarly journals CheY1 and CheY2 of Azorhizobium caulinodans ORS571 Regulate Chemotaxis and Competitive Colonization with the Host Plant

2020 ◽  
Vol 86 (15) ◽  
Author(s):  
Wei Liu ◽  
Xue Bai ◽  
Yan Li ◽  
Jun Min ◽  
Yachao Kong ◽  
...  
Keyword(s):  
Response Regulator ◽  
Bacterial Chemotaxis ◽  
Nodule Formation ◽  
Sesbania Rostrata ◽  
Azorhizobium Caulinodans ◽  
Response Regulators ◽  
Free Living ◽  
Content Type ◽  
Colonization Ability ◽  
Cell Phenotypes

ABSTRACT The genome of Azorhizobium caulinodans ORS571 encodes two chemotaxis response regulators: CheY1 and CheY2. cheY1 is located in a chemotaxis cluster (cheAWY1BR), while cheY2 is located 37 kb upstream of the cheAWY1BR cluster. To determine the contributions of CheY1 and CheY2, we compared the wild type (WT) and mutants in the free-living state and in symbiosis with the host Sesbania rostrata. Swim plate tests and capillary assays revealed that both CheY1 and CheY2 play roles in chemotaxis, with CheY2 having a more prominent role than CheY1. In an analysis of the swimming paths of free-swimming cells, the ΔcheY1 mutant exhibited decreased frequency of direction reversal, whereas the ΔcheY2 mutant appeared to change direction much more frequently than the WT. Exopolysaccharide (EPS) production in the ΔcheY1 and ΔcheY2 mutants was lower than that in the WT, but the ΔcheY2 mutant had more obvious EPS defects that were similar to those of the ΔcheY1 ΔcheY2 and Δeps1 mutants. During symbiosis, the levels of competitiveness for root colonization and nodule occupation of ΔcheY1 and ΔcheY2 mutants were impaired compared to those of the WT. Moreover, the competitive colonization ability of the ΔcheY2 mutant was severely impaired compared to that of the ΔcheY1 mutant. Taken together, the ΔcheY2 phenotypes are more severe than the ΔcheY1 phenotype in free-living and symbiotic states, and that of the double mutant resembles the ΔcheY2 single-mutant phenotype. These defects of ΔcheY1 and ΔcheY2 mutants were restored to the WT phenotype by complementation. These results suggest that there are different regulatory mechanisms of CheY1 and CheY2 and that CheY2 is a key chemotaxis regulator under free-living and symbiosis conditions. IMPORTANCE Azorhizobium caulinodans ORS571 is a motile soil bacterium that has the dual capacity to fix nitrogen both under free-living conditions and in symbiosis with Sesbania rostrata, forming nitrogen-fixing root and stem nodules. Bacterial chemotaxis to chemoattractants derived from host roots promotes infection and subsequent nodule formation by directing rhizobia to appropriate sites of infection. In this work, we identified and demonstrated that CheY2, a chemotactic response regulator encoded by a gene outside the chemotaxis cluster, is required for chemotaxis and multiple other cell phenotypes. CheY1, encoded by a gene in the chemotaxis cluster, also plays a role in chemotaxis. Two response regulators mediate bacterial chemotaxis and motility in different ways. This work extends the understanding of the role of multiple response regulators in Gram-negative bacteria.

scholarly journals The Sinorhizobium melilotintrXGene Is Involved in Succinoglycan Production, Motility, and Symbiotic Nodulation on Alfalfa

2013 ◽  
Vol 79 (23) ◽  
pp. 7150-7159 ◽  
Author(s):  
Dong Wang ◽  
Haiying Xue ◽  
Yiwen Wang ◽  
Ruochun Yin ◽  
Fang Xie ◽  
...  
Keyword(s):  
Sinorhizobium Meliloti ◽  
Nitrogen Starvation ◽  
Response Regulator ◽  
Insertion Mutant ◽  
Sesbania Rostrata ◽  
Symbiotic Relationship ◽  
Azorhizobium Caulinodans ◽  
Free Living ◽  
Content Type ◽  
Regulatory Systems

ABSTRACTRhizobia 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 inAzorhizobium caulinodans, is required for free-living nitrogen metabolism and symbiotic nodulation onSesbania rostrata. However, its functions in a typical rhizobium such asSinorhizobium melilotiremain unclear. Here we found that theS. melilotiresponse 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 ofntrXformed 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 thentrXmutant were small and displayed symptoms of nitrogen starvation. Interestingly, the deletion mutant ofntrYshowed a phenotype similar to that of the parent strain. These findings demonstrate that theS. melilotiNtrX is a new regulator of succinoglycan production and motility that is not genetically coupled with NtrY.

scholarly journals A Chemotaxis Receptor Modulates Nodulation during the Azorhizobium caulinodans-Sesbania rostrata Symbiosis

2016 ◽  
Vol 82 (11) ◽  
pp. 3174-3184 ◽  
Author(s):  
Nan Jiang ◽  
Wei Liu ◽  
Yan Li ◽  
Hailong Wu ◽  
Zhenhai Zhang ◽  
...  
Keyword(s):  
Mutant Strain ◽  
Type Strain ◽  
Wild Type Strain ◽  
Bacterial Chemotaxis ◽  
Sesbania Rostrata ◽  
Nitrogen Fixing ◽  
Azorhizobium Caulinodans ◽  
Wild Type ◽  
Free Living ◽  
Content Type

ABSTRACTAzorhizobium caulinodansORS571 is a free-living nitrogen-fixing bacterium which can induce nitrogen-fixing nodules both on the root and the stem of its legume hostSesbania 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 ofA. caulinodanscontaining an N-terminal PAS domain, named IcpB. IcpB is a soluble heme-binding protein that localized at the cell poles. AnicpBmutant strain was impaired in sensing oxygen gradients and in chemotaxis response to organic acids. Compared to the wild-type strain, theicpBmutant strain was also affected in the production of extracellular polysaccharides and impaired in flocculation. When inoculated alone, theicpBmutant induced nodules onS. rostrata, but the nodules formed were smaller and had reduced N2-fixing activity. TheicpBmutant 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 theA. caulinodans-S. rostratasymbiosis.IMPORTANCEBacterial chemotaxis has been implicated in the establishment of various plant-microbe associations, including that of rhizobial symbionts with their legume host. The exact signal(s) detected by the motile bacteria that guide them to their plant hosts remain poorly characterized.Azorhizobium caulinodansORS571 is a diazotroph that is a motile and chemotactic rhizobial symbiont ofSesbania rostrata, where it forms nitrogen-fixing nodules on both the roots and the stems of the legume host. We identify here a chemotaxis receptor sensing oxygen inA. caulinodansthat is critical for nodulation and nitrogen fixation on the stems and roots ofS. rostrata. These results identify oxygen sensing and chemotaxis as key regulators of theA. caulinodans-S. rostratasymbiosis.

scholarly journals FixJ family regulator AcfR of Azorhizobium caulinodans is involved in symbiosis with the host plant

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Wei Liu ◽  
Xue Bai ◽  
Yan Li ◽  
Haikun Zhang ◽  
Xiaoke Hu
Keyword(s):  
Signal Transduction ◽  
Host Plant ◽  
Type Strain ◽  
Wild Type Strain ◽  
Response Regulator ◽  
Azorhizobium Caulinodans ◽  
Wild Type ◽  
Response Regulators ◽  
Free Living ◽  
Two Component

Abstract Background A wide variety of bacterial adaptative responses to environmental conditions are mediated by signal transduction pathways. Two-component signal transduction systems are one of the predominant means used by bacteria to sense the signals of the host plant and adjust their interaction behaviour. A total of seven open reading frames have been identified as putative two-component response regulators in the gram-negative nitrogen-fixing bacteria Azorhizobium caulinodans ORS571. However, the biological functions of these response regulators in the symbiotic interactions between A. caulinodans ORS571 and the host plant Sesbania rostrata have not been elucidated to date. Results In this study, we identified and investigated a two-component response regulator, AcfR, with a phosphorylatable N-terminal REC (receiver) domain and a C-terminal HTH (helix-turn-helix) LuxR DNA-binding domain in A. caulinodans ORS571. Phylogenetic analysis showed that AcfR possessed close evolutionary relationships with NarL/FixJ family regulators. In addition, six histidine kinases containing HATPase_c and HisKA domains were predicted to interact with AcfR. Furthermore, the biological function of AcfR in free-living and symbiotic conditions was elucidated by comparing the wild-type strain and the ΔacfR mutant strain. In the free-living state, the cell motility behaviour and exopolysaccharide production of the ΔacfR mutant were significantly reduced compared to those of the wild-type strain. In the symbiotic state, the ΔacfR mutant showed a competitive nodule defect on the stems and roots of the host plant, suggesting that AcfR can provide A. caulinodans with an effective competitive ability for symbiotic nodulation. Conclusions Our results showed that AcfR, as a response regulator, regulates numerous phenotypes of A. caulinodans under the free-living conditions and in symbiosis with the host plant. The results of this study help to elucidate the involvement of a REC + HTH_LuxR two-component response regulator in the Rhizobium-host plant interaction.

scholarly journals Involvement of the Azorhizobial Chromosome Partition Gene (parA) in the Onset of Bacteroid Differentiation during Sesbania rostrata Stem Nodule Development

2011 ◽  
Vol 77 (13) ◽  
pp. 4371-4382 ◽  
Author(s):  
Chi-Te Liu ◽  
Kyung-Bum Lee ◽  
Yu-Sheng Wang ◽  
Min-Hua Peng ◽  
Kung-Ta Lee ◽  
...  
Keyword(s):  
Cell Shape ◽  
Deletion Mutant ◽  
Nodule Development ◽  
Sesbania Rostrata ◽  
Gene Transcript ◽  
Azorhizobium Caulinodans ◽  
Free Living ◽  
Content Type ◽  
Chromosome Partitioning ◽  
Cellular Development

ABSTRACTAparAgene in-frame deletion mutant ofAzorhizobium caulinodansORS571 (ORS571-ΔparA) was constructed to evaluate the roles of the chromosome-partitioning gene on various bacterial traits and on the development of stem-positioned nodules. The ΔparAmutant showed a pleiomorphic cell shape phenotype and was polyploid, with differences in nucleoid sizes due to dramatic defects in chromosome partitioning. Upon inoculation of the ΔparAmutant onto the stem ofSesbania rostrata, three types of immature nodule-like structures with impaired nitrogen-fixing activity were generated. Most showed signs of bacteroid early senescence. Moreover, the ΔparAcells within the nodule-like structures exhibited multiple developmental-stage phenotypes. Since thebacAgene has been considered an indicator for bacteroid formation, we applied the expression pattern ofbacAas a nodule maturity index in this study. Our data indicate that thebacAgene expression isparAdependent in symbiosis. The presence of theparAgene transcript was inversely correlated with the maturity of nodule; the transcript was switched off in fully mature bacteroids. In summary, our experimental evidence demonstrates that theparAgene not only plays crucial roles in cellular development when the microbe is free-living but also negatively regulates bacteroid formation inS. rostratastem nodules.

scholarly journals Cellular Stoichiometry of Chemotaxis Proteins in Sinorhizobium meliloti

2020 ◽  
Vol 202 (14) ◽  
Author(s):  
Timofey D. Arapov ◽  
Rafael Castañeda Saldaña ◽  
Amanda L. Sebastian ◽  
W. Keith Ray ◽  
Richard F. Helm ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Bacillus Subtilis ◽  
Sinorhizobium Meliloti ◽  
Response Regulator ◽  
Bacterial Chemotaxis ◽  
Adaptor Proteins ◽  
Molar Ratio ◽  
Content Type ◽  
Chemotaxis Proteins ◽  
Chemotaxis System

ABSTRACT Chemotaxis systems enable microbes to sense their immediate environment, moving toward beneficial stimuli and away from those that are harmful. In an effort to better understand the chemotaxis system of Sinorhizobium meliloti, a symbiont of the legume alfalfa, the cellular stoichiometries of all ten chemotaxis proteins in S. meliloti were determined. A combination of quantitative immunoblot and mass spectrometry revealed that the protein stoichiometries in S. meliloti varied greatly from those in Escherichia coli and Bacillus subtilis. To compare protein ratios to other systems, values were normalized to the central kinase CheA. All S. meliloti chemotaxis proteins exhibited increased ratios to various degrees. The 10-fold higher molar ratio of adaptor proteins CheW1 and CheW2 to CheA might result in the formation of rings in the chemotaxis array that consist of only CheW instead of CheA and CheW in a 1:1 ratio. We hypothesize that the higher ratio of CheA to the main response regulator CheY2 is a consequence of the speed-variable motor in S. meliloti, instead of a switch-type motor. Similarly, proteins involved in signal termination are far more abundant in S. meliloti, which utilizes a phosphate sink mechanism based on CheA retrophosphorylation to inactivate the motor response regulator versus CheZ-catalyzed dephosphorylation as in E. coli and B. subtilis. Finally, the abundance of CheB and CheR, which regulate chemoreceptor methylation, was increased compared to CheA, indicative of variations in the adaptation system of S. meliloti. Collectively, these results mark significant differences in the composition of bacterial chemotaxis systems. IMPORTANCE The symbiotic soil bacterium Sinorhizobium meliloti contributes greatly to host-plant growth by fixing atmospheric nitrogen. The provision of nitrogen as ammonium by S. meliloti leads to increased biomass production of its legume host alfalfa and diminishes the use of environmentally harmful chemical fertilizers. To better understand the role of chemotaxis in host-microbe interaction, a comprehensive catalogue of the bacterial chemotaxis system is vital, including its composition, function, and regulation. The stoichiometry of chemotaxis proteins in S. meliloti has very few similarities to the systems in Escherichia coli and Bacillus subtilis. In addition, total amounts of proteins are significantly lower. S. meliloti exhibits a chemotaxis system distinct from known models by incorporating new proteins as exemplified by the phosphate sink mechanism.

scholarly journals The RapP-PhrP Quorum-Sensing System of Bacillus subtilis Strain NCIB3610 Affects Biofilm Formation through Multiple Targets, Due to an Atypical Signal-Insensitive Allele of RapP

2014 ◽  
Vol 197 (3) ◽  
pp. 592-602 ◽  
Author(s):  
Shira Omer Bendori ◽  
Shaul Pollak ◽  
Dorit Hizi ◽  
Avigdor Eldar
Keyword(s):  
Bacillus Subtilis ◽  
Quorum Sensing ◽  
Biofilm Formation ◽  
Response Regulator ◽  
Subtilis Strain ◽  
Transcriptional Level ◽  
Response Regulators ◽  
Multiple Targets ◽  
Content Type ◽  
Negative Effect

The genome ofBacillus subtilis168 encodes eightrap-phrquorum-sensing pairs. Rap proteins of all characterized Rap-Phr pairs inhibit the function of one or several important response regulators: ComA, Spo0F, or DegU. This inhibition is relieved upon binding of the peptide encoded by the cognatephrgene.Bacillus subtilisstrain NCIB3610, the biofilm-proficient ancestor of strain 168, encodes, in addition, therapP-phrPpair on the plasmid pBS32. RapP was shown to dephosphorylate Spo0F and to regulate biofilm formation, but unlike other Rap-Phr pairs, RapP does not interact with PhrP. In this work we extend the analysis of the RapP pathway by reexamining its transcriptional regulation, its effect on downstream targets, and its interaction with PhrP. At the transcriptional level, we show thatrapPandphrPregulation is similar to that of otherrap-phrpairs. We further find that RapP has an Spo0F-independent negative effect on biofilm-related genes, which is mediated by the response regulator ComA. Finally, we find that the insensitivity of RapP to PhrP is due to a substitution of a highly conserved residue in the peptide binding domain of therapPallele of strain NCIB3610. Reversing this substitution to the consensus amino acid restores the PhrP dependence of RapP activity and eliminates the effects of therapP-phrPlocus on ComA activity and biofilm formation. Taken together, our results suggest that RapP strongly represses biofilm formation through multiple targets and that PhrP does not counteract RapP due to a rare mutation inrapP.

scholarly journals FimY Does Not Interfere with FimZ-FimW Interaction during Type 1 Fimbria Production by Salmonella enterica Serovar Typhimurium

2013 ◽  
Vol 81 (12) ◽  
pp. 4453-4460 ◽  
Author(s):  
Sarah A. Zeiner ◽  
Brett E. Dwyer ◽  
Steven Clegg
Keyword(s):  
Salmonella Enterica ◽  
Salmonella Enterica Serovar Typhimurium ◽  
Response Regulator ◽  
Response Regulators ◽  
Content Type ◽  
Component Systems ◽  
The Family ◽  
Serovar Typhimurium ◽  
Two Component Systems

ABSTRACTThe production of type 1 fimbriae inSalmonella entericaserovar Typhimurium is controlled, in part, by three proteins, FimZ, FimY, and FimW. Amino acid sequence analysis indicates that FimZ belongs to the family of bacterial response regulators of two-component systems. In these studies, we have demonstrated that introducing a mutation mimicking phosphorylation of FimZ is necessary for activation of its target gene,fimA. In addition, the interaction of FimZ with FimW, a repressor offimAexpression, occurs only when FimZ is phosphorylated. Consequently, the negative regulatory effect of FimW is most likely due to downmodulation of the active FimZ protein. FimY does not appear to function as a response regulator, and its activity can be lost by mimicking the phosphorylation of FimY. Overproduction of FimY cannot alleviate the nonfimbriate phenotype in a FimZ mutant, whereas high levels of FimZ can overcome the nonfimbriate phenotype of a FimY mutant. It appears that FimY acts upstream of FimZ to activatefimAexpression.

scholarly journals A Dual Role of Amino Acids from Sesbania rostrata Seed Exudates in the Chemotaxis Response of Azorhizobium caulinodans ORS571

2019 ◽  
Vol 32 (9) ◽  
pp. 1134-1147 ◽  
Author(s):  
Xiaolin Liu ◽  
Zhihong Xie ◽  
Yixuan Wang ◽  
Yu Sun ◽  
Xiaoxiao Dang ◽  
...  
Keyword(s):  
Amino Acids ◽  
Dual Role ◽  
Chemotactic Response ◽  
Nodule Formation ◽  
Sesbania Rostrata ◽  
Azorhizobium Caulinodans ◽  
Regulation Of Expression ◽  
Chemotaxis Proteins ◽  
Azorhizobium Caulinodans Ors571

Azorhizobium caulinodans ORS571 can induce nodule formation on the roots and the stems of its host legume, Sesbania rostrata. Plant exudates are essential in the dialogue between microbes and their host plant and, in particular, amino acids can play an important role in the chemotactic response of bacteria. Histidine, arginine, and aspartate, which are the three most abundant amino acids present in S. rostrata seed exudates, behave as chemoattractants toward A. caulinodans. A position-specific-iterated BLAST analysis of the methyl-accepting chemotaxis proteins (MCPs) (chemoreceptors) in the genome of A. caulinodans was performed. Among the 43 MCP homologs, two MCPs harboring a dCache domain were selected as possible cognate amino acid MCPs. After analysis of relative gene expression levels and construction of a gene-deleted mutant strain, one of them, AZC_0821 designed as TlpH, was confirmed to be responsible for the chemotactic response to the three amino acids. In addition, it was found that these three amino acids can also influence chemotaxis of A. caulinodans independently of the chemosensory receptors, by being involved in the increase of the expression level of several che and fla genes involved in the chemotaxis pathway and flagella synthesis. Thus, the contribution of amino acids present in seed exudates is directly related to the role as chemoattractants and indirectly related to the role in the regulation of expression of key genes involved in chemotaxis and motility. This “dual role” is likely to influence the formation of biofilms by A. caulinodans and the host root colonization properties of this bacterium.

scholarly journals Identification of the Three Genes Involved in Controlling Production of a Phytotoxin Tropolone in Burkholderia plantarii

2016 ◽  
Vol 198 (11) ◽  
pp. 1604-1609 ◽  
Author(s):  
Shunpei Miwa ◽  
Eri Kihira ◽  
Akinori Yoshioka ◽  
Kaoru Nakasone ◽  
Sho Okamoto ◽  
...  
Keyword(s):  
Signal Transduction ◽  
Response Regulator ◽  
Rice Seedling ◽  
Seedling Blight ◽  
Response Regulators ◽  
Two Component System ◽  
Content Type ◽  
Bacterial Signal Transduction ◽  
Genes Encoding ◽  
Cognate Response Regulator

ABSTRACTTropolone, a phytotoxin produced byBurkholderia plantarii, causes rice seedling blight. To identify genes involved in tropolone synthesis, we systematically constructed mutations in the genes encoding 55 histidine kinases and 72 response regulators. From the resulting defective strains, we isolated three mutants, KE1, KE2, and KE3, in which tropolone production was repressed. The deleted genes of these mutants were namedtroR1,troK, andtroR2, respectively. The mutant strains did not cause rice seedling blight, and complementation experiments indicated that TroR1, TroK, and TroR2 were involved in the synthesis of tropolone inB. plantarii. However, tropolone synthesis was repressed in the TroR1 D52A, TroK H253A, and TroR2 D46A site-directed mutants. These results suggest that the putative sensor kinase (TroK) and two response regulators (TroR1 and TroR2) control the production of tropolone inB. plantarii.IMPORTANCEA two-component system is normally composed of a sensor histidine kinase (HK) and a cognate response regulator (RR) pair. In this study, HK (TroK) and two RRs (TroR1 and TroR2) were found to be involved in controlling tropolone production inB. plantarii. These three genes may be part of a bacterial signal transduction network. Such networks are thought to exist in other bacteria to regulate phytotoxin production, as well as environmental adaptation and signal transduction.

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