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 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 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 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.”

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.

scholarly journals Role of Quorum Sensing in Sinorhizobium meliloti-Alfalfa Symbiosis

2009 ◽  
Vol 191 (13) ◽  
pp. 4372-4382 ◽  
Author(s):  
Nataliya Gurich ◽  
Juan E. González
Keyword(s):  
Quorum Sensing ◽  
Plant Invasion ◽  
Sinorhizobium Meliloti ◽  
Growth Cycle ◽  
Signal Molecules ◽  
Wild Type ◽  
In Planta ◽  
Cell Functions ◽  
Sensing System ◽  
Quorum Sensing System

ABSTRACT The ExpR/Sin quorum-sensing system of the gram-negative soil bacterium Sinorhizobium meliloti plays an important role in the establishment of symbiosis with its host plant Medicago sativa. A mutant unable to produce autoinducer signal molecules (sinI) is deficient in its ability to invade the host, but paradoxically, a strain lacking the quorum-sensing transcriptional regulator ExpR is as efficient as the wild type. We compared the whole-genome expression profile of the wild-type strain with strains missing one of the quorum-sensing regulatory components to identify genes controlled by the ExpR/Sin system throughout the different phases of the bacterial growth cycle, as well as in planta. Our analyses revealed that ExpR is a highly versatile regulator with a unique ability to show different regulatory capabilities in the presence or absence of an autoinducer. In addition, this study provided us with insight into the plant invasion defect displayed by the autoinducer mutant. We also discovered that the ExpR/Sin quorum-sensing system is repressed after plant invasion. Therefore, quorum sensing plays a crucial role in the regulation of many cell functions that ensures the successful invasion of the host and is inactivated once symbiosis is established.

scholarly journals Identification of Two Quorum-Sensing Systems in Sinorhizobium meliloti

2002 ◽  
Vol 184 (13) ◽  
pp. 3466-3475 ◽  
Author(s):  
Melanie M. Marketon ◽  
Juan E. González
Keyword(s):  
Quorum Sensing ◽  
Sinorhizobium Meliloti ◽  
Screening Method ◽  
Free Living ◽  
Sensing System ◽  
Sensing Systems ◽  
Its Gene ◽  
Quorum Sensing System ◽  
Host Signaling ◽  
The Difference

ABSTRACT Sinorhizobium meliloti is a free-living soil bacterium which is capable of establishing a symbiotic relationship with the alfalfa plant (Medicago sativa). This symbiosis involves a network of bacterium-host signaling, as well as the potential for bacterium-bacterium communication, such as quorum sensing. In this study, we characterized the production of N-acyl homoserine lactones (AHLs) by two commonly used S. meliloti strains, AK631 and Rm1021. We found that AK631 produces at least nine different AHLs, while Rm1021 produces only a subset of these molecules. To address the difference in AHL patterns between the strains, we developed a novel screening method to identify the genes affecting AHL synthesis. With this screening method, chromosomal groEL (groELc) was shown to be required for synthesis of the AHLs that are unique to AK631 but not for synthesis of the AHLs that are made by both AK631 and Rm1021. We then used the screening procedure to identify a mutation in a gene homologous to traM of Agrobacterium tumefaciens, which was able to suppress the phenotype of the groELc mutation. A traR homolog was identified immediately upstream of traM, and we propose that its gene product requires a functional groELc for activity and is also responsible for inducing the synthesis of the AHLs that are unique to AK631. We show that the traR/traM locus is part of a quorum-sensing system unique to AK631 and propose that this locus is involved in regulating conjugal plasmid transfer. We also present evidence for the existence of a second quorum-sensing system, sinR/sinI, which is present in both AK631 and Rm1021.

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