scholarly journals The LuxR Homolog ExpR, in Combination with the Sin Quorum Sensing System, Plays a Central Role in Sinorhizobium meliloti Gene Expression

2004 ◽  
Vol 186 (16) ◽  
pp. 5460-5472 ◽  
Author(s):  
Hanh H. Hoang ◽  
Anke Becker ◽  
Juan E. González
Keyword(s):  
Gene Expression ◽  
Quorum Sensing ◽  
Sinorhizobium Meliloti ◽  
Regulation Of Gene Expression ◽  
Bacterial Communication ◽  
Cellular Processes ◽  
Sensing System ◽  
Dna Microarray Data ◽  
Luxr Homolog ◽  
Quorum Sensing System

ABSTRACT Quorum sensing, a population density-dependent mechanism for bacterial communication and gene regulation, plays a crucial role in the symbiosis between alfalfa and its symbiont Sinorhizobium meliloti. The Sin system, one of three quorum sensing systems present in S. meliloti, controls the production of the symbiotically active exopolysaccharide EPS II. Based on DNA microarray data, the Sin system also seems to regulate a multitude of S. meliloti genes, including genes that participate in low-molecular-weight succinoglycan production, motility, and chemotaxis, as well as other cellular processes. Most of the regulation by the Sin system is dependent on the presence of the ExpR regulator, a LuxR homolog. Gene expression profiling data indicate that ExpR participates in additional cellular processes that include nitrogen fixation, metabolism, and metal transport. Based on our microarray analysis we propose a model for the regulation of gene expression by the Sin/ExpR quorum sensing system and another possible quorum sensing system(s) in S. meliloti.

scholarly journals Quorum Sensing Controls Exopolysaccharide Production in Sinorhizobium meliloti

2003 ◽  
Vol 185 (1) ◽  
pp. 325-331 ◽  
Author(s):  
Melanie M. Marketon ◽  
Sarah A. Glenn ◽  
Anatol Eberhard ◽  
Juan E. González
Keyword(s):  
Gene Expression ◽  
Quorum Sensing ◽  
Sinorhizobium Meliloti ◽  
Wild Type Strain ◽  
Homoserine Lactone ◽  
Symbiotic Relationship ◽  
Wild Type ◽  
Sensing System ◽  
Quorum Sensing System

ABSTRACT Sinorhizobium meliloti is a soil bacterium capable of invading and establishing a symbiotic relationship with alfalfa plants. This invasion process requires the synthesis, by S. meliloti, of at least one of the two symbiotically important exopolysaccharides, succinoglycan and EPS II. We have previously shown that the sinRI locus of S. meliloti encodes a quorum-sensing system that plays a role in the symbiotic process. Here we show that the sinRI locus exerts one level of control through regulation of EPS II synthesis. Disruption of the autoinducer synthase gene, sinI, abolished EPS II production as well as the expression of several genes in the exp operon that are responsible for EPS II synthesis. This phenotype was complemented by the addition of acyl homoserine lactone (AHL) extracts from the wild-type strain but not from a sinI mutant, indicating that the sinRI-specified AHLs are required for exp gene expression. This was further confirmed by the observation that synthetic palmitoleyl homoserine lactone (C16:1-HL), one of the previously identified sinRI-specified AHLs, specifically restored exp gene expression. Most importantly, the absence of symbiotically active EPS II in a sinI mutant was confirmed in plant nodulation assays, emphasizing the role of quorum sensing in symbiosis.

scholarly journals Regulation of Motility by the ExpR/Sin Quorum-Sensing System in Sinorhizobium meliloti

2007 ◽  
Vol 190 (3) ◽  
pp. 861-871 ◽  
Author(s):  
Hanh H. Hoang ◽  
Nataliya Gurich ◽  
Juan E. González
Keyword(s):  
Gene Expression ◽  
Quorum Sensing ◽  
Sinorhizobium Meliloti ◽  
Flagellar Apparatus ◽  
Sensing System ◽  
Physiological Processes ◽  
Genome Expression ◽  
Proposed Model ◽  
Quorum Sensing System ◽  
Whole Genome Expression

ABSTRACT A successful symbiotic relationship between Sinorhizobium meliloti and its host Medicago sativa (alfalfa) depends on several signaling mechanisms, such as the biosynthesis of exopolysaccharides (EPS) by S. meliloti. Previous work in our laboratory has shown that a quorum-sensing mechanism controls the production of the symbiotically active EPS II. Recent microarray analysis of the whole-genome expression profile of S. meliloti reveals that the ExpR/Sin quorum-sensing system regulates additional physiological processes that include low-molecular-weight succinoglycan production, nitrogen utilization, metal transport, motility, and chemotaxis. Nearly half of the flagellar genes and their dependence on quorum sensing are prominently displayed in our microarray analyses. We extend those observations in this work and confirm the findings by real-time PCR expression analysis of selected genes, including the flaF, flbT, flaC, cheY1, and flgB genes, involved in motility and chemotaxis. These genes code for regulators of flagellum synthesis, the chemotactic response, or parts of the flagellar apparatus. Gene expression analyses and visualization of flagella by electron microscopy performed at different points in the growth phase support our proposed model in which quorum sensing downregulates motility in S. meliloti. We demonstrate that the ExpR/Sin quorum-sensing system controls motility gene expression through the VisN/VisR/Rem relay. We also show that the ExoS-dependent two-component system suppresses motility gene expression through VisN and Rem in parallel to quorum sensing. This study contributes to our understanding of the mechanisms that govern motility in S. meliloti.

scholarly journals The ExpR/Sin Quorum-Sensing System Controls Succinoglycan Production in Sinorhizobium meliloti

2007 ◽  
Vol 189 (19) ◽  
pp. 7077-7088 ◽  
Author(s):  
Sarah A. Glenn ◽  
Nataliya Gurich ◽  
Morgan A. Feeney ◽  
Juan E. González
Keyword(s):  
Molecular Weight ◽  
Quorum Sensing ◽  
Medicago Sativa ◽  
Sinorhizobium Meliloti ◽  
Direct Synthesis ◽  
Low Molecular Weight ◽  
Plant Host ◽  
Gram Negative ◽  
Sensing System ◽  
Quorum Sensing System

ABSTRACT Sinorhizobium meliloti is a gram-negative soil bacterium capable of forming a symbiotic nitrogen-fixing relationship with its plant host, Medicago sativa. Various bacterially produced factors are essential for successful nodulation. For example, at least one of two exopolysaccharides produced by S. meliloti (succinoglycan or EPS II) is required for nodule invasion. Both of these polymers are produced in high- and low-molecular-weight (HMW and LMW, respectively) fractions; however, only the LMW forms of either succinoglycan or EPS II are active in nodule invasion. The production of LMW succinoglycan can be generated by direct synthesis or through the depolymerization of HMW products by the action of two specific endoglycanases, ExsH and ExoK. Here, we show that the ExpR/Sin quorum-sensing system in S. meliloti is involved in the regulation of genes responsible for succinoglycan biosynthesis as well as in the production of LMW succinoglycan. Therefore, quorum sensing, which has been shown to regulate the production of EPS II, also plays an important role in succinoglycan biosynthesis.

scholarly journals An Orphan LuxR Homolog of Sinorhizobium meliloti Affects Stress Adaptation and Competition for Nodulation

2008 ◽  
Vol 75 (4) ◽  
pp. 946-955 ◽  
Author(s):  
Arati V. Patankar ◽  
Juan E. Gonz�lez
Keyword(s):  
Sinorhizobium Meliloti ◽  
Wild Type Strain ◽  
Symbiotic Association ◽  
Response Regulators ◽  
Sensing System ◽  
Luxr Homolog ◽  
Active Methyl ◽  
Quorum Sensing System ◽  
Type Response

ABSTRACT The Sin/ExpR quorum-sensing system of Sinorhizobium meliloti plays an important role in the symbiotic association with its host plant, Medicago sativa. The LuxR-type response regulators of the Sin system include the synthase (SinI)-associated SinR and the orphan regulator ExpR. Interestingly, the S. meliloti Rm1021 genome codes for four additional putative orphan LuxR homologs whose regulatory roles remain to be identified. These response regulators contain the characteristic domains of the LuxR family of proteins, which include an N-terminal autoinducer/response regulatory domain and a C-terminal helix-turn-helix domain. This study elucidates the regulatory role of one of the orphan LuxR-type response regulators, NesR. Through expression and phenotypic analyses, nesR was determined to affect the active methyl cycle of S. meliloti. Moreover, nesR was shown to influence nutritional and stress response activities in S. meliloti. Finally, the nesR mutant was deficient in competing with the wild-type strain for plant nodulation. Taken together, these results suggest that NesR potentially contributes to the adaptability of S. meliloti when it encounters challenges such as high osmolarity, nutrient starvation, and/or competition for nodulation, thus increasing its chances for survival in the stressful rhizosphere.

scholarly journals Effector-Stimulated Single Molecule Protein-DNA Interactions of a Quorum-Sensing System in Sinorhizobium meliloti

2007 ◽  
Vol 92 (12) ◽  
pp. 4391-4400 ◽  
Author(s):  
Frank Wilco Bartels ◽  
Matthew McIntosh ◽  
Alexander Fuhrmann ◽  
Christoph Metzendorf ◽  
Patrik Plattner ◽  
...  
Keyword(s):  
Quorum Sensing ◽  
Single Molecule ◽  
Sinorhizobium Meliloti ◽  
Dna Interactions ◽  
Sensing System ◽  
Protein Dna Interactions ◽  
Quorum Sensing System

scholarly journals Characterization of the Sinorhizobium meliloti sinR/sinI Locus and the Production of Novel N-Acyl Homoserine Lactones

2002 ◽  
Vol 184 (20) ◽  
pp. 5686-5695 ◽  
Author(s):  
Melanie M. Marketon ◽  
Matthew R. Gronquist ◽  
Anatol Eberhard ◽  
Juan E. González
Keyword(s):  
Quorum Sensing ◽  
Sinorhizobium Meliloti ◽  
Short Chain ◽  
Homoserine Lactones ◽  
Sensing System ◽  
Acyl Homoserine Lactones ◽  
Quorum Sensing System ◽  
Acyl Chains ◽  
Novel Structures

ABSTRACT Sinorhizobium meliloti is a soil bacterium which can establish a nitrogen-fixing symbiosis with the legume Medicago sativa. Recent work has identified a pair of genes, sinR and sinI, which represent a potential quorum-sensing system and are responsible for the production of N-acyl homoserine lactones (AHLs) in two S. meliloti strains, Rm1021 and Rm41. In this work, we characterize the sinRI locus and show that these genes are responsible for the synthesis of several long-chain AHLs ranging from 12 to 18 carbons in length. Four of these, 3-oxotetradecanoyl HL, 3-oxohexadecenoyl HL, hexadecenoyl HL, and octadecanoyl HL, have novel structures. This is the first report of AHLs having acyl chains longer than 14 carbons. We show that a disruption in sinI eliminates these AHLs and that a sinR disruption results in only basal levels of the AHLs. Moreover, the same sinI and sinR mutations also lead to a decrease in the number of pink nodules during nodulation assays, as well as a slight delay in the appearance of pink nodules, indicating a role for quorum sensing in symbiosis. We also show that sinI and sinR mutants are still capable of producing several short-chain AHLs, one of which was identified as octanoyl HL. We believe that these short-chain AHLs are evidence of a second quorum-sensing system in Rm1021, which we refer to here as the mel system, for “S. meliloti.”

Peculiarities of the SprIR Quorum Sensing System of Serratia proteamaculans 94 and Its Involvement in Regulation of Cellular Processes

2021 ◽  
Vol 57 (2) ◽  
pp. 161-172
Author(s):  
Yu. V. Zaitseva ◽  
V. A. Lipasova ◽  
O. A. Koksharova ◽  
V. A. Plyuta ◽  
I. V. Demidyuk ◽  
...  
Keyword(s):  
Quorum Sensing ◽  
Cellular Processes ◽  
Sensing System ◽  
Serratia Proteamaculans ◽  
Quorum Sensing System

scholarly journals Sinorhizobium meliloti Regulator MucR Couples Exopolysaccharide Synthesis and Motility

2008 ◽  
Vol 21 (11) ◽  
pp. 1498-1509 ◽  
Author(s):  
Christelle Bahlawane ◽  
Matthew McIntosh ◽  
Elizaveta Krol ◽  
Anke Becker
Keyword(s):  
Quorum Sensing ◽  
Promoter Region ◽  
Sinorhizobium Meliloti ◽  
Homoserine Lactone ◽  
Bacterial Attachment ◽  
Sequence Motif ◽  
Sensing System ◽  
Regulatory Systems ◽  
Quorum Sensing System ◽  
Regulation Mechanisms

In order to enter symbiosis with its legume partner, Sinorhizobium meliloti requires regulatory systems for the appropriate responses to its environment. For example, motility is required for the chemotactic movement of bacteria toward the compounds released by its host, and exopolysaccharides (EPS) are required for bacterial attachment to the root or for invasion of the infection thread. Previous research has shown that ExoR/ExoS/ChvI as well as the ExpR/Sin quorum-sensing system inversely regulate both motility and EPS production, although the regulation mechanisms were unknown. We were able to attribute the ExpR-mediated regulation of motility to the ability of ExpR to bind a DNA sequence upstream of visN when activated by N-acyl-homoserine lactone. Furthermore, MucR, previously characterized as a regulator of EPS production, also affected motility. MucR inhibited expression of rem encoding an activator of motility gene expression and, consequently, the expression of Rem-regulated genes such as flaF and flgG. Binding of MucR to the rem promoter region was demonstrated and a sequence motif similar to the previously identified MucR binding consensus was identified within this region. The swarming ability of S. meliloti Rm2011 was shown to depend on a functional ExpR/Sin quorum-sensing system and the production of both flagella and EPS. Finally, we propose a model for the coordination of motility and EPS synthesis in S. meliloti.

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