scholarly journals Autoregulation of Sinorhizobium meliloti exoR gene expression

Microbiology ◽  
2010 ◽  
Vol 156 (7) ◽  
pp. 2092-2101 ◽  
Author(s):  
Hai-Yang Lu ◽  
Hai-Ping Cheng
Keyword(s):  
Sinorhizobium Meliloti ◽  
Carbon Sources ◽  
Regulatory System ◽  
Leguminous Plant ◽  
Wild Type ◽  
Plant Host ◽  
Active Sensor ◽  
Bacterial Exopolysaccharide ◽  
Membrane Bound ◽  
And Control

The successful nitrogen-fixing symbiosis between the Gram-negative soil bacterium Sinorhizobium meliloti and its leguminous plant host alfalfa (Medicago sativa) requires the bacterial exopolysaccharide succinoglycan. Succinoglycan and flagellum production, along with the ability to metabolize more than 20 different carbon sources and control the expression of a large number of S. meliloti genes, is regulated by the ExoR–ExoS/ChvI signalling pathway. The ExoR protein interacts with and suppresses the sensing activities of ExoS, the membrane-bound sensor of the ExoS/ChvI two-component regulatory system. Here we show that exoR expression is clearly upregulated in the absence of any functional ExoR protein. This upregulation was suppressed by the presence of the wild-type ExoR protein but not by a mutated ExoR protein lacking signal peptide. The levels of exoR expression could be directly modified in real time by changing the levels of total ExoR protein. The expression of exoR was also upregulated by the constitutively active sensor mutation exoS96, and blocked by two single mutations, exoS* and exoSsupA , in the ExoS sensing domain. Presence of the wild-type ExoS protein further elevated the levels of exoR expression in the absence of functional ExoR protein, and reversed the effects of exoS96, exoS* and exoSsupA mutations. Altogether, these data suggest that ExoR protein autoregulates exoR expression through the ExoS/ChvI system, allowing S. meliloti cells to maintain the levels of exoR expression based on the amount of total ExoR protein.

scholarly journals Sinorhizobium meliloti Mutants Lacking Phosphotransferase System Enzyme HPr or EIIA Are Altered in Diverse Processes, Including Carbon Metabolism, Cobalt Requirements, and Succinoglycan Production

2008 ◽  
Vol 190 (8) ◽  
pp. 2947-2956 ◽  
Author(s):  
Catalina Arango Pinedo ◽  
Ryan M. Bringhurst ◽  
Daniel J. Gage
Keyword(s):  
Carbon Metabolism ◽  
Sinorhizobium Meliloti ◽  
Carbon Sources ◽  
Deletion Mutants ◽  
Symbiotic Relationship ◽  
Wild Type ◽  
Phosphotransferase System ◽  
Carbon Utilization ◽  
Carbon Regulation ◽  
Extreme Sensitivity

ABSTRACT Sinorhizobium meliloti is a member of the Alphaproteobacteria that fixes nitrogen when it is in a symbiotic relationship. Genes for an incomplete phosphotransferase system (PTS) have been found in the genome of S. meliloti. The genes present code for Hpr and ManX (an EIIAMan-type enzyme). HPr and EIIA regulate carbon utilization in other bacteria. hpr and manX in-frame deletion mutants exhibited altered carbon metabolism and other phenotypes. Loss of HPr resulted in partial relief of succinate-mediated catabolite repression, extreme sensitivity to cobalt limitation, rapid die-off during stationary phase, and altered succinoglycan production. Loss of ManX decreased expression of melA-agp and lac, the operons needed for utilization of α- and β-galactosides, slowed growth on diverse carbon sources, and enhanced accumulation of high-molecular-weight succinoglycan. A strain with both hpr and manX deletions exhibited phenotypes similar to those of the strain with a single hpr deletion. Despite these strong phenotypes, deletion mutants exhibited wild-type nodulation and nitrogen fixation when they were inoculated onto Medicago sativa. The results show that HPr and ManX (EIIAMan) are involved in more than carbon regulation in S. meliloti and suggest that the phenotypes observed occur due to activity of HPr or one of its phosphorylated forms.

scholarly journals The Novel Genes emmABC Are Associated with Exopolysaccharide Production, Motility, Stress Adaptation, and Symbiosis in Sinorhizobium meliloti

2009 ◽  
Vol 191 (19) ◽  
pp. 5890-5900 ◽  
Author(s):  
Jennifer Morris ◽  
Juan E. González
Keyword(s):  
Sinorhizobium Meliloti ◽  
Genetic Factors ◽  
Leguminous Plant ◽  
The Novel ◽  
Two Component System ◽  
Cell Component ◽  
Plant Host ◽  
Free Living ◽  
Novel Genes ◽  
Exopolysaccharide Production

ABSTRACT The nitrogen-fixing symbiont Sinorhizobium meliloti senses and responds to constantly changing environmental conditions as it makes its way through the soil in search of its leguminous plant host, Medicago sativa (alfalfa). As a result, this bacterium regulates various aspects of its physiology in order to respond appropriately to stress, starvation, and competition. For example, exopolysaccharide production, which has been shown to play an important role in the ability of S. meliloti to successfully invade its host, also helps the bacterium withstand osmotic changes and other environmental stresses. In an effort to further elucidate the intricate regulation of this important cell component, we set out to identify genetic factors that may affect its production. Here we characterize novel genes that encode a small protein (EmmA) and a putative two-component system (EmmB-EmmC). A mutation in any of these genes leads to increased production of the symbiotically important exopolysaccharide succinoglycan. In addition, emm mutants display membrane-associated defects, are nonmotile, and are unable to form an optimal symbiosis with alfalfa, suggesting that these novel genes may play a greater role in the overall fitness of S. meliloti both during the free-living stage and in its association with its host.

scholarly journals Characterization of a Two-Component Regulatory System That Regulates Succinate-Mediated Catabolite Repression in Sinorhizobium meliloti

2010 ◽  
Vol 192 (21) ◽  
pp. 5725-5735 ◽  
Author(s):  
Preston P. Garcia ◽  
Ryan M. Bringhurst ◽  
Catalina Arango Pinedo ◽  
Daniel J. Gage
Keyword(s):  
Catabolite Repression ◽  
Sinorhizobium Meliloti ◽  
Response Regulator ◽  
Energy State ◽  
Carbon Sources ◽  
Regulatory System ◽  
Dicarboxylic Acids ◽  
Deletion Mutants ◽  
State Monitoring ◽  
Secondary Carbon

ABSTRACT When they are available, Sinorhizobium meliloti utilizes C4-dicarboxylic acids as preferred carbon sources for growth while suppressing the utilization of some secondary carbon sources such as α- and β-galactosides. The phenomenon of using succinate as the sole carbon source in the presence of secondary carbon sources is termed succinate-mediated catabolite repression (SMCR). Genetic screening identified the gene sma0113 as needed for strong SMCR when S. meliloti was grown in succinate plus lactose, maltose, or raffinose. sma0113 and the gene immediately downstream, sma0114, encode the proteins Sma0113, an HWE histidine kinase with five PAS domains, and Sma0114, a CheY-like response regulator lacking a DNA-binding domain. sma0113 in-frame deletion mutants show a relief of catabolite repression compared to the wild type. sma0114 in-frame deletion mutants overproduce polyhydroxybutyrate (PHB), and this overproduction requires sma0113. Sma0113 may use its five PAS domains for redox level or energy state monitoring and use that information to regulate catabolite repression and related responses.

scholarly journals The FixM Flavoprotein Modulates Inhibition by AICAR or 5′AMP of Respiratory and Nitrogen Fixation Gene Expression in Sinorhizobium meliloti

2002 ◽  
Vol 15 (6) ◽  
pp. 598-607 ◽  
Author(s):  
Céline Cosseau ◽  
Anne Marie Garnerone ◽  
Jacques Batut
Keyword(s):  
Gene Expression ◽  
Nitrogen Fixation ◽  
Sinorhizobium Meliloti ◽  
Regulatory System ◽  
Wild Type ◽  
Meliloti Strain ◽  
Related Metabolite ◽  
Nitrogen Fixation Gene ◽  
Nifa Gene

AICAR, a purine-related metabolite, was recently shown to inhibit respiratory and nifA gene expression in Sinorhizobium meliloti. Here, we demonstrate that AICAR has essentially no or little effect in a wild-type S. meliloti strain and inhibits respiratory and nitrogen fixation gene expression only in specific mutant backgrounds. We have analyzed in detail a mutant in which addition of AICAR inhibited fixK, fixN, fixT, and nifA expression. The corresponding gene, fixM, is located just downstream of fixK1 on pSymA megaplasmid and encodes a flavoprotein oxidore-ductase. 5′AMP, a structural analogue of AICAR, mimicked AICAR effect as well as the nucleoside precursors AICAriboside and adenosine. The mode of action of AICAR and 5′AMP in vivo was investigated. We demonstrate that AICAR does not affect FixK transcriptional activity and instead regulates fixK and nifA gene expression. We hypothesize that AICAR and 5′AMP may modulate, possibly indirectly, the activity of the FixLJ two-component regulatory system. The possible physiological roles of AICAR, 5′AMP, and fixM in the context of symbiosis are discussed.

scholarly journals ExpR Coordinates the Expression of Symbiotically Important, Bundle-Forming Flp Pili with Quorum Sensing in Sinorhizobium meliloti

2014 ◽  
Vol 80 (8) ◽  
pp. 2429-2439 ◽  
Author(s):  
Hardik M. Zatakia ◽  
Cassandra E. Nelson ◽  
Umair J. Syed ◽  
Birgit E. Scharf
Keyword(s):  
Quorum Sensing ◽  
Sinorhizobium Meliloti ◽  
Consensus Sequence ◽  
Homoserine Lactone ◽  
Host Cells ◽  
Wild Type ◽  
Mobility Shift ◽  
Plant Host ◽  
Symbiotic Interaction ◽  
Content Type

ABSTRACTType IVb pili in enteropathogenic bacteria function as a host colonization factor by mediating tight adherence to host cells, but their role in bacterium-plant symbiosis is currently unknown. The genome of the symbiotic soil bacteriumSinorhizobium meliloticontains two clusters encoding proteins for type IVb pili of the Flp (fimbrial low-molecular-weight protein) subfamily. To establish the role of Flp pili in the symbiotic interaction ofS. melilotiand its host,Medicago sativa, we deletedpilA1, which encodes the putative pilin subunit in the chromosomalflp-1cluster and conducted competitive nodulation assays. ThepilA1deletion strain formed 27% fewer nodules than the wild type. Transmission electron microscopy revealed the presence of bundle-forming pili protruding from the polar and lateral region ofS. melilotiwild-type cells. The putative pilus assembly ATPase CpaE1 fused to mCherry showed a predominantly unilateral localization. Transcriptional reporter gene assays demonstrated that expression ofpilA1peaks in early stationary phase and is repressed by the quorum-sensing regulator ExpR, which also controls production of exopolysaccharides and motility. Binding of acyl homoserine lactone-activated ExpR to thepilA1promoter was confirmed with electrophoretic mobility shift assays. A 17-bp consensus sequence for ExpR binding was identified within the 28-bp protected region by DNase I footprinting analyses. Our results show that Flp pili are important for efficient symbiosis ofS. melilotiwith its plant host. The temporal inverse regulation of exopolysaccharides and pili by ExpR enablesS. melilotito achieve a coordinated expression of cellular processes during early stages of host interaction.

scholarly journals ExoS/ChvI Two-Component Signal-Transduction System Activated in the Absence of Bacterial Phosphatidylcholine

2021 ◽  
Vol 12 ◽  
Author(s):  
Otto Geiger ◽  
Christian Sohlenkamp ◽  
Diana Vera-Cruz ◽  
Daniela B. Medeot ◽  
Lourdes Martínez-Aguilar ◽  
...  
Keyword(s):  
Sinorhizobium Meliloti ◽  
Regulatory System ◽  
Deficient Mutant ◽  
Wild Type ◽  
Membrane Phospholipids ◽  
Two Component System ◽  
Two Component ◽  
Two Component Signal Transduction ◽  
Suppressor Mutants ◽  
Transcript Profiles

Sinorhizobium meliloti contains the negatively charged phosphatidylglycerol and cardiolipin as well as the zwitterionic phosphatidylethanolamine (PE) and phosphatidylcholine (PC) as major membrane phospholipids. In previous studies we had isolated S. meliloti mutants that lack PE or PC. Although mutants deficient in PE are able to form nitrogen-fixing nodules on alfalfa host plants, mutants lacking PC cannot sustain development of any nodules on host roots. Transcript profiles of mutants unable to form PE or PC are distinct; they differ from each other and they are different from the wild type profile. For example, a PC-deficient mutant of S. meliloti shows an increase of transcripts that encode enzymes required for succinoglycan biosynthesis and a decrease of transcripts required for flagellum formation. Indeed, a PC-deficient mutant is unable to swim and overproduces succinoglycan. Some suppressor mutants, that regain swimming and form normal levels of succinoglycan, are altered in the ExoS sensor. Our findings suggest that the lack of PC in the sinorhizobial membrane activates the ExoS/ChvI two-component regulatory system. ExoS/ChvI constitute a molecular switch in S. meliloti for changing from a free-living to a symbiotic life style. The periplasmic repressor protein ExoR controls ExoS/ChvI function and it is thought that proteolytic ExoR degradation would relieve repression of ExoS/ChvI thereby switching on this system. However, as ExoR levels are similar in wild type, PC-deficient mutant and suppressor mutants, we propose that lack of PC in the bacterial membrane provokes directly a conformational change of the ExoS sensor and thereby activation of the ExoS/ChvI two-component system.

scholarly journals Sinorhizobium meliloti Sulfotransferase That Modifies Lipopolysaccharide

2004 ◽  
Vol 186 (13) ◽  
pp. 4168-4176 ◽  
Author(s):  
Glen E. Cronan ◽  
David H. Keating
Keyword(s):  
Cell Surface ◽  
Sinorhizobium Meliloti ◽  
Capsular Polysaccharide ◽  
Genomic Sequence ◽  
Wild Type ◽  
Plant Structure ◽  
Plant Host ◽  
Nod Factor

ABSTRACT Sinorhizobium meliloti is a gram-negative soil bacterium found either in free-living form or as a nitrogen-fixing endosymbiont of a plant structure called the nodule. Symbiosis between S. meliloti and its plant host alfalfa is dependent on bacterial transcription of nod genes, which encode the enzymes responsible for synthesis of Nod factor. S. meliloti Nod factor is a lipochitooligosaccharide that undergoes a sulfate modification essential for its biological activity. Sulfate also modifies the carbohydrate substituents of the bacterial cell surface, including lipopolysaccharide (LPS) and capsular polysaccharide (K-antigen) (R. A. Cedergren, J. Lee, K. L. Ross, and R. I. Hollingsworth, Biochemistry 34:4467-4477, 1995). We utilized the genomic sequence of S. meliloti to identify an open reading frame, SMc04267 (which we now propose to name lpsS), which encodes an LPS sulfotransferase activity. We expressed LpsS in Escherichia coli and demonstrated that the purified protein functions as an LPS sulfotransferase. Mutants lacking LpsS displayed an 89% reduction in LPS sulfotransferase activity in vitro. However, lpsS mutants retain approximately wild-type levels of sulfated LPS when assayed in vivo, indicating the presence of an additional LPS sulfotransferase activity(ies) in S. meliloti that can compensate for the loss of LpsS. The lpsS mutant did show reduced LPS sulfation, compared to that of the wild type, under conditions that promote nod gene expression, and it elicited a greater number of nodules than did the wild type during symbiosis with alfalfa. These results suggest that sulfation of cell surface polysaccharides and Nod factor may compete for a limiting pool of intracellular sulfate and that LpsS is required for optimal LPS sulfation under these conditions.

scholarly journals AniA Regulates Reserve Polymer Accumulation and Global Protein Expression in Rhizobium etli

2002 ◽  
Vol 184 (8) ◽  
pp. 2287-2295 ◽  
Author(s):  
Sergio Encarnación ◽  
María del Carmen Vargas ◽  
Michael F. Dunn ◽  
Araceli Dávalos ◽  
Guillermo Mendoza ◽  
...  
Keyword(s):  
Protein Expression ◽  
Gene Product ◽  
Sinorhizobium Meliloti ◽  
Carbon Sources ◽  
Proteome Analysis ◽  
Extracellular Polysaccharide ◽  
Oxidative Capacity ◽  
Nucleotide Sequencing ◽  
Rhizobium Etli ◽  
Wild Type

ABSTRACT Previously, it was reported that the oxidative capacity and ability to grow on carbon sources such as pyruvate and glucose were severely diminished in the Rhizobium etli phaC::ΩSmr/Spr mutant CAR1, which is unable to synthesize poly-β-hydroxybutyric acid (PHB) (M. A. Cevallos, S. Encarnación, A. Leija, Y. Mora, and J. Mora, J. Bacteriol. 178:1646-1654, 1996). By random Tn5 mutagenesis of the phaC strain, we isolated the mutants VEM57 and VEM58, both of which contained single Tn5 insertions and had recovered the ability to grow on pyruvate or glucose. Nucleotide sequencing of the region surrounding the Tn5 insertions showed that they had interrupted an open reading frame designated aniA based on its high deduced amino acid sequence identity to the aniA gene product of Sinorhizobium meliloti. R. etli aniA was located adjacent to and divergently transcribed from genes encoding the PHB biosynthetic enzymes β-ketothiolase (PhaA) and acetoacetyl coenzyme A reductase (PhaB). An aniA::Tn5 mutant (VEM5854) was constructed and found to synthesize only 40% of the wild type level of PHB. Both VEM58 and VEM5854 produced significantly more extracellular polysaccharide than the wild type. Organic acid excretion and levels of intracellular reduced nucleotides were lowered to wild-type levels in VEM58 and VEM5854, in contrast to those of strain CAR1, which were significantly elevated. Proteome analysis of VEM58 showed a drastic alteration of protein expression, including the absence of a protein identified as PhaB. We propose that the aniA gene product plays an important role in directing carbon flow in R. etli.

scholarly journals Characterization of Sinorhizobium meliloti Triose Phosphate Isomerase Genes

2007 ◽  
Vol 189 (9) ◽  
pp. 3445-3451 ◽  
Author(s):  
Nathan J. Poysti ◽  
Ivan J. Oresnik
Keyword(s):  
Sole Carbon Source ◽  
Sinorhizobium Meliloti ◽  
Symbiotic Nitrogen Fixation ◽  
Carbon Sources ◽  
Triose Phosphate Isomerase ◽  
Central Metabolism ◽  
Wild Type ◽  
Triose Phosphate ◽  
Encoding Gene

ABSTRACT A Tn5 mutant strain of Sinorhizobium meliloti with an insertion in tpiA (systematic identifier SMc01023), a putative triose phosphate isomerase (TPI)-encoding gene, was isolated. The tpiA mutant grew more slowly than the wild type on rhamnose and did not grow with glycerol as a sole carbon source. The genome of S. meliloti wild-type Rm1021 contains a second predicted TPI-encoding gene, tpiB (SMc01614). We have constructed mutations and confirmed that both genes encode functional TPI enzymes. tpiA appears to be constitutively expressed and provides the primary TPI activity for central metabolism. tpiB has been shown to be required for growth with erythritol. TpiB activity is induced by growth with erythritol; however, basal levels of TpiB activity present in tpiA mutants allow for growth with gluconeogenic carbon sources. Although tpiA mutants can be complemented by tpiB, tpiA cannot substitute for mutations in tpiB with respect to erythritol catabolism. Mutations in tpiA or tpiB alone do not cause symbiotic defects; however, mutations in both tpiA and tpiB caused reduced symbiotic nitrogen fixation.

scholarly journals Cooperativity in Signal Transfer through the Uhp System of Escherichia coli

2002 ◽  
Vol 184 (15) ◽  
pp. 4205-4210 ◽  
Author(s):  
Daniël T. Verhamme ◽  
Pieter W. Postma ◽  
Wim Crielaard ◽  
Klaas J. Hellingwerf
Keyword(s):  
Response Regulator ◽  
Regulatory System ◽  
Phosphoryl Transfer ◽  
Transmembrane Signaling ◽  
Wild Type ◽  
Positive Cooperativity ◽  
Extracellular Glucose ◽  
Membrane Bound ◽  
The Relationship

ABSTRACT The UhpABC regulatory system in enterobacteria controls the expression of the hexose phosphate transporter UhpT. Signaling is initiated through sensing of extracellular glucose 6-phosphate by membrane-bound UhpC, which in turn modulates the histidine-protein kinase UhpB. Together with the cytoplasmic response regulator UhpA, they constitute a typical two-component regulatory system based on His-to-Asp phosphoryl transfer. Activated (i.e., phosphorylated) UhpA binds to the promoter region of uhpT, resulting in initiation of transcription. We have investigated the contribution of transmembrane signaling (through UhpBC) and intracellular activation (through UhpA) to the overall Uhp response (UhpT expression) in vivo. UhpA activation could be made independent of transmembrane signaling when ΔuhpBC cells were grown on pyruvate. Inorganic phosphate interfered with glucose 6-phosphate-dependent, UhpBC-mediated, as well as pyruvate-mediated activation of UhpA. The relationship between the concentration of inducer (glucose 6-phosphate) and the Uhp induction rate was nonhyperbolic, indicating positive cooperativity. The degree of cooperativity was affected by the carbon or energy source available to the cells for growth. As pyruvate-mediated activation of UhpA in ΔuhpBC cells could result in considerably stronger UhpT expression than glucose 6-phosphate-dependent activation through UhpBC, the observed positive cooperativity for the overall pathway in wild-type cells may reflect the previously described cooperative binding of UhpA to the uhpT promoter (J. L. Dahl et al., J. Biol. Chem. 272:1910-1919, 1997).

Sign in / Sign up

Export Citation Format

Share Document