Rhizobium meliloti exopolysaccharides: genetic analyses and symbiotic importance

1991 ◽  
Vol 19 (3) ◽  
pp. 636-644 ◽  
Author(s):  
T. Lynne Reuber ◽  
Jason Reed ◽  
Jane Glazebrook ◽  
M. Alexandra Glucksmann ◽  
Dianne Ahmann ◽  
...  
Keyword(s):  
Rhizobium Meliloti ◽  
Nodule Development ◽  
Nitrogen Fixing ◽  
Free Living ◽  
Genetic Analyses ◽  
Living State ◽  
Meliloti Strain

Summary Genetic experiments have indicated that succinoglycan (EPS I), the acidic Calcofluor-binding exopolysaccharide, of the nitrogen-fixing bacterium Rhizobium meliloti strain Rm1021 is required for nodule invasion and possibly for later events in nodule development on alfalfa and other hosts. Fourteen exo loci on the second megaplasmid have been identified that are required for, or affect, the synthesis of EPS I. Mutations in certain of these loci completely abolish the production of EPS I and result in mutants that form empty Fix- nodules. We have identified two loci, exoR and exoS, that are involved in the regulation of EPS I synthesis in the free-living state. Certain exo mutations which completely abolish EPS I production are lethal in an exoR95 or exoS96 background. Histochemical analyses of the expression of exo genes during nodulation using exo :: TnphoA fusions have indicated that the exo genes are expressed most strongly in the invasion zone. In addition, we have discovered that R. meliloti has a latent capacity to synthesize a second exopolysaccharide (EPS II) that can substitute for the role(s) of EPS I in nodulation of alfalfa but not of other hosts. Possible roles for exopolysaccharides in symbiosis are discussed.

scholarly journals Nodule-Specific Cysteine-Rich Peptides Negatively Regulate Nitrogen-Fixing Symbiosis in a Strain-Specific Manner in Medicago truncatula

2018 ◽  
Vol 31 (2) ◽  
pp. 240-248 ◽  
Author(s):  
Qi Wang ◽  
Jinge Liu ◽  
Hua Li ◽  
Shengming Yang ◽  
Peter Körmöczi ◽  
...  
Keyword(s):  
Medicago Truncatula ◽  
Sinorhizobium Meliloti ◽  
Molecular Mechanisms ◽  
Nodule Development ◽  
Nitrogen Fixing ◽  
Plant Genotype ◽  
Specific Manner ◽  
Meliloti Strain ◽  
High Level ◽  
Symbiotic Partner

Medicago truncatula shows a high level of specificity when interacting with its symbiotic partner Sinorhizobium meliloti. This specificity is mainly manifested at the nitrogen-fixing stage of nodule development, such that a particular bacterial strain forms nitrogen-fixing nodules (Nod+/Fix+) on one plant genotype but ineffective nodules (Nod+/Fix−) on another. Recent studies have just begun to reveal the underlying molecular mechanisms that control this specificity. The S. meliloti strain A145 induces the formation of Fix+ nodules on the accession DZA315.16 but Fix− nodules on Jemalong A17. A previous study reported that the formation of Fix− nodules on Jemalong A17 by S. meliloti A145 was conditioned by a single recessive allele named Mtsym6. Here we demonstrate that the specificity associated with S. meliloti A145 is controlled by multiple genes in M. truncatula, including NFS1 and NFS2 that encode nodule-specific cysteine-rich (NCR) peptides. The two NCR peptides acted dominantly to block rather than promote nitrogen fixation by S. meliloti A145. These two NCR peptides are the same ones that negatively regulate nitrogen-fixing symbiosis associated with S. meliloti Rm41.

scholarly journals Artificial activation of nif gene expression in nodule bacteria Ex Planta

2019 ◽  
Vol 17 (2) ◽  
pp. 35-42
Author(s):  
Andrey K. Baymiev ◽  
Roman S. Gumenko ◽  
Anastasiya A. Vladimirova ◽  
Ekaterina S. Akimova ◽  
Zilya R. Vershinina ◽  
...  
Keyword(s):  
Nitrogen Fixation ◽  
Nitrogenase Activity ◽  
Regulatory Protein ◽  
Inducible Promoter ◽  
Nitrogen Fixing ◽  
Nodule Bacteria ◽  
Free Living ◽  
Living State ◽  
Artificial Activation ◽  
Nifa Gene

Background. Rhizobia are the most effective nitrogen-fixing organisms that can fix nitrogen only in symbiosis with leguminous plants. The general transcriptional activator of nitrogen fixation genes in diazotrophic bacteria is NifA. In this work, the possibility of modifying the regulation of nitrogen fixation in the nodule bacteria Mesorhizobium, Ensifer and Rhizobium was studied by introducing an additional copy of the nifA gene into the bacterial genomes during the regulation of induced bacterial promoters. Materials and methods. A series of expression genetic constructs with NifA genes of nodule bacteria strains under the control of an inducible promoter Pm were created. The resulting constructs were transformed into strains of nodule bacteria. The obtained recombinant strains were investigated for the appearance of their nitrogen-fixing activity in the free-living state. Results. It was shown that the expression of nifA in recombinant cells of all three genera of bacteria leads to the appearance of insignificant nitrogenase activity. At the same time, the level of nitrogenase activity does not have a correlation with the level of expression of the introduced nifA gene, which, most likely, is a consequence of the multilevel regulation of nitrogen fixation. Conclusion. The possibility of artificial activation of nitrogenase activity in nodule bacteria in the free-living state by introducing the NifA regulatory protein gene into bacteria was shown.

scholarly journals Diversity of free-Living nitrogen fixing Streptomyces in soils of the badlands of South Dakota

2017 ◽  
Vol 195 ◽  
pp. 31-39 ◽  
Author(s):  
Bibha Dahal ◽  
Gitanjali NandaKafle ◽  
Lora Perkins ◽  
Volker S. Brözel
Keyword(s):  
South Dakota ◽  
Nitrogen Fixing ◽  
Free Living

scholarly journals Effect of Abandonment on Diversity and Abundance of Free-Living Nitrogen-Fixing Bacteria and Total Bacteria in the Cropland Soils of Hulun Buir, Inner Mongolia

PLoS ONE ◽  
2014 ◽  
Vol 9 (9) ◽  
pp. e106714 ◽  
Author(s):  
Huhe ◽  
Shinchilelt Borjigin ◽  
Yunxiang Cheng ◽  
Nobukiko Nomura ◽  
Toshiaki Nakajima ◽  
...  
Keyword(s):  
Inner Mongolia ◽  
Nitrogen Fixing ◽  
Nitrogen Fixing Bacteria ◽  
Free Living ◽  
Total Bacteria

Expression of the nodulation and nitrogen fixation genes in Rhizobium meliloti during development

Genome ◽  
1989 ◽  
Vol 31 (1) ◽  
pp. 354-360 ◽  
Author(s):  
San Chiun Shen ◽  
Shui Ping Wang ◽  
Guan Qiao Yu ◽  
Jia Bi Zhu
Keyword(s):  
Nitrogen Fixation ◽  
Rhizobium Meliloti ◽  
Abnormal Development ◽  
Wild Type ◽  
Free Living ◽  
Nod Genes ◽  
Nodule Initiation ◽  
Fix Genes ◽  
Nitrogen Fixation Genes

Genes that specify nodulation (nod genes) are only active in the free-living rhizobia or in the nodule initiation state of rhizobia. As soon as the repression of nod genes occurs in the bacteroids of the nodule, nifA is induced, while ntrC is inactivated and thus the nifA-mediated nif/fix genes are turned on. Limitation of available oxygen brings about the induction of nifA, which reflects the actual status of nif/fix gene activities in symbiotic state of rhizobia. Oxygen thus appears to be a major symbiotic signal to the expression of bacteroid nif/fix genes. Mutation of nifA or shortage of nifA product in wild-type rhizobia caused by the inhibition of multicopy nifH/fixA promoters leads to an abnormal development of nodules and premature degradation of bacteroids in nodules.Key words: nitrogen fixation, nodulation, nif/fix regulation, nifA mutant.

Kinetics of first-cutting regrowth of alfalfa plants and nitrogenase activity in a controlled environment with and without added nitrate

1983 ◽  
Vol 61 (9) ◽  
pp. 2405-2409 ◽  
Author(s):  
F. D. H. Macdowall
Keyword(s):  
Dry Matter ◽  
Rhizobium Meliloti ◽  
Nitrogenase Activity ◽  
Radical Change ◽  
N Nutrition ◽  
Meliloti Strain ◽  
Medicago Sativa L ◽  
Reducing Activity ◽  
Acetylene Reducing Activity ◽  
Kinetics Of

Seedlings of Medicago sativa L. cv. Algonquin were grown in vermiculite and nodulated by Rhizobium meliloti strain 102F70 at two lower levels of N, until flowering when the tops were cut off to leave about 10% shoot stubble. Residual shoot dry matter immediately resumed first-order growth and maintained it throughout regrowth to second flowering. The rate constants of shoot regrowth were 34% lower (at 15 mM NO3−), 25% lower (at 1.5 mM NO3− symbiotically), or 220% higher (at zero NO3− symbiotically) than the values for 1 to 4-week-old seedlings, which indicated a radical change in physiology. Root dry matter resumed exponential growth after a 7-day recession and its recovery and yields were independent of N nutrition. The most pronounced minima occurred in the acetylene-reducing activity of nitrogenase, the kinetics of which paralleled root dry matter except that its redevelopment stopped after two-thirds of the regrowth time. The rate coefficient for the redevelopment of nitrogenase activity equalled that for its development during the seedling stage, which suggested unchanged limitations on that process until its redevelopment stopped.

Plasmid replicons of Rhizobium

2005 ◽  
Vol 33 (1) ◽  
pp. 157-158 ◽  
Author(s):  
L.C. Crossman
Keyword(s):  
Short Review ◽  
Nitrogen Fixing ◽  
Rhizobium Etli ◽  
Free Living ◽  
Leguminous Plants ◽  
Symbiotic Plasmid ◽  
Rhizobium Spp ◽  
Plasmid Replicons ◽  
Rhizobium Sp

Rhizobium spp. are found in soil. They are both free-living and found symbiotically associated with the nodules of leguminous plants. Traditionally, studies have focused on the association of these organisms with plants in nitrogen-fixing nodules, since this is regarded as the most important role of these bacteria in the environment. Rhizobium sp. are known to possess several replicons. Some, like the Rhizobium etli symbiotic plasmid p42d and the plasmid pNGR234b of Rhizobium NGR234, have been sequenced and characterized. The plasmids from these organisms are the focus of this short review.

Detection of Rhizobium meliloti cells in field soil and nodules by polymerase chain reaction

1995 ◽  
Vol 41 (9) ◽  
pp. 816-825 ◽  
Author(s):  
R. J. Watson ◽  
C. Haitas-Crockett ◽  
T. Martin ◽  
R. Heys
Keyword(s):  
Polymerase Chain Reaction ◽  
Rhizobium Meliloti ◽  
Genetically Engineered ◽  
Chain Reaction ◽  
Pcr Inhibitor ◽  
Vertical Location ◽  
Meliloti Strain ◽  
Identification Of Bacteria ◽  
Polymerase Chain ◽  
Genetically Engineered Microorganism

A genetically marked Rhizobium meliloti strain, R692, was prepared by insertion of a 1.7-kb DNA segment from Tn903 between the nifHDK and fixABC genes in the nod megaplasmid. This DNA was used as a marker, detectable by polymerase chain reaction (PCR), for the specific identification of bacteria in soil samples and alfalfa nodules. This detection technique was tested by applying different titres of the marked strain to field plots seeded with alfalfa. Samples of soil and nodules were assayed for the presence of the marker DNA fragment by PCR using primers specific to the marker sequence. The experiments revealed that the bacteria could be detected directly in soil containing about 103–104 bacteria/g, but greater sensitivity was prevented by potent PCR inhibitors present in the samples. The titre of the bacteria in the soil decreased rapidly after inoculation, dropping about 10-fold per week. Tests of vertical location of the bacteria in soil cores showed that the bacteria were initially dispersed to a depth of 18 cm, and subsequently retained viability in the top 2–8 cm. As few as 10 marked R. meliloti per gram of soil resulted in its establishment at detectable levels in nodules. Application of about 104–105 bacteria/g soil was sufficient to give the maximum number of nodules per plant and resulted in 70–90% occupancy by the marked strain. Limited movement of the inoculant was detected by analysis of nodules from plants adjacent to the sites where the bacteria were applied, probably by movement in water. The experiments demonstrated the advantages of PCR for the monitoring of marked microorganisms in the environment.Key words: genetically engineered microorganism, PCR inhibitor, nitrogen fixation, nif and fix genes, genetic marker.

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