MucR is necessary for galactoglucan production in Sinorhizobium meliloti EFB1
M Martín1, J Lloret, M Sánchez-Contreras
1Departamento de Biología, Universidad Autónoma de Madrid, Spain.
Abstract:
Sinorhizobium meliloti can produce two types of acidic exopolysaccharides, succinoglycan and galactoglucan, that are interchangeable for infection of alfalfa nodules. Strain SU47 and derivatives produce only succinoglycan, unless it grows under phosphate limitation or carries a mutation in either of two regulatory loci, mucR or expR. It has been proposed that MucR acts as a transcriptional repressor that blocks the expression of the exp genes responsible for galactoglucan production. Strain EFB1 simultaneously produces both exopolysaccharides. Heterologous expression of lacZ transcriptional fusions of the expE promoters has shown that genetic background is more important that promoter sequence for exp gene expression, since expE promoters from both strains are expressed at high level in EFB1 and not in SU47. We have found that mucR is present in mucoid and nonmucoid strains, and in EFB1 differs from SU47 in only one conservative amino acid change. MucR proteins from both strains are interchangeable. An mucR mutant of EFB1 cannot produce galactoglucan and does not express mucS.
Insights
Sinorhizobium meliloti produces two exopolysaccharides, succinoglycan and galactoglucan, crucial for alfalfa nodule infection. The study reveals MucR protein
Area of Science:
- Microbiology
- Plant-microbe interactions
- Bacterial genetics
Background:
- Sinorhizobium meliloti synthesizes succinoglycan and galactoglucan, exopolysaccharides vital for alfalfa nodule symbiosis.
- Galactoglucan production is regulated by loci mucR and expR, with MucR proposed as a transcriptional repressor.
- Strain EFB1 produces both exopolysaccharides, while SU47 primarily produces succinoglycan.
Purpose of the Study:
- To investigate the role of MucR in regulating galactoglucan synthesis in Sinorhizobium meliloti.
- To understand the genetic basis for differential exopolysaccharide production between strains SU47 and EFB1.
- To analyze the function and conservation of the MucR protein.
Main Methods:
- Utilizing lacZ transcriptional fusions to study expE promoter activity in different genetic backgrounds.
- Comparing MucR protein sequences between mucoid and nonmucoid strains.
- Generating mucR mutants to assess their impact on exopolysaccharide production.
Main Results:
- ExpE promoters showed high expression in EFB1 and low expression in SU47, indicating genetic background influences gene expression.
- The mucR gene is conserved in both mucoid and nonmucoid strains.
- A single conservative amino acid change was observed in MucR between strains SU47 and EFB1, with both proteins being interchangeable.
- An EFB1 mucR mutant lost the ability to produce galactoglucan and did not express mucS.
Conclusions:
- Genetic background, rather than promoter sequence, is critical for exp gene expression in Sinorhizobium meliloti.
- MucR plays a key role in repressing galactoglucan production.
- The MucR protein is highly conserved and functionally interchangeable between strains with different exopolysaccharide production profiles.
More Related Videos
11:45Fluorescence Live-cell Imaging of the Complete Vegetative Cell Cycle of the Slow-growing Social Bacterium Myxococcus xanthus
Published on: June 20, 2018
08:51Profiling of Permethylated Mucin O-glycans Using Matrix-assisted Laser Desorption/Ionization Time-of-flight Mass Spectrometry
Published on: June 20, 2025
Related Concept Videos
01:24Oligosaccharide Assembly
Multiple sugar molecules that may or may...
01:25Inducible Operons: lac Operon