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  • 1
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-072X
    Keywords: Attachment ; Rhizobium ; Rhicadhesin ; Ca2+ ; Pea root hairs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The first step in attachment of Rhizobiaceae cells to plant root hair tips is mediated by a Ca2+-dependent, Ca2+-binding protein, rhicadhesin. The possible role of Ca2+ in synthesis, anchoring and activity of rhicadhesin was investigated. Growth of Rhizobium leguminosarum biovar viciae cells under Ca2+-limitation was found to result in loss of attachment ability. Under these conditions, rhicadhesin could not be usolated from the bacterial cell surface, but was found to be excreted in the growth medium. Divalent ions appeared to be essential for the ability of purified rhicadhesin to inhibit attachment of R. leguminosarum biovar viciae cells to pea root hair tips. Calcium ions were found not to be involved in binding of rhicadhesin to the plant surface, but appeared to be involved in anchoring of the adhesin to the bacterial cell surface. A model for the role of Ca2+ in activity of rhicadhesin is presented.
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  • 3
    ISSN: 1432-072X
    Keywords: Rhizobium leguminosarum ; Nodulation mutants ; Hair curling ; Infection thread ; Sym plasmid ; Complementation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Thirty Tn5- or Tn1831-induced nodulation (nod) mutants of Rhizobium leguminosarum were examined for their genetic and symbiotic properties. Thirteen mutants contained a deletion in Sym plasmid pRL1JI. These deletions cover the whole nod region and are 50 kb in size. All remaining seventeen mutations are located in a 6.6 kb EcoRI nod fragment of the Sym plasmid. Mutations in a 3.5 kb part on the right hand side of this 6.6 kb fragment completely prevent nodulation on Vicia sativa. All mutants in this 3.5 kb area are unable to induce marked root hair curling and thick and short roots. Mutations in a 1.5 kb area on the left hand side of the 6.6 kb nod fragment generate other symbiotic defects in that nodules are only rarely formed and only so after a delay of several days. Moreover, infection thread formation is delayed and root hair curling is more excessive than that caused by the parental strain. Their ability to induce thick and short roots is unaltered. Mutations in this 1.5 kb region are not complemented by pRmSL26, which carries nod genes of R. meliloti, whereas mutations in the 3.5 kb region are all complemented by pRmSL26.
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  • 4
    ISSN: 1432-072X
    Keywords: Key words:Agrobacterium–β-1,2-Glucan –chvB Mutants – Ca2+
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. The chvB gene of Agrobacterium tumefaciens encodes a 235 kDa proteinaceous intermediate involved in the synthesis of β-1,2-glucan. chvB mutants show a pleiotropic phenotype. Besides not to produce cyclic β-1,2-glucan, chvB mutants have been reported to be avirulent, attachment-deficient, and nonmotile. In this study we report additional differences from the parent strain, probably all linked to changes in the cell envelope. This pleiotropic phenotype – except for attachment and virulence – could largely be prevented by growing chvB cells with low levels of calcium. Although a role for β-1,2-glucan in osmoadaptation has been proposed, the mode of action of β-1,2-glucan is not known. We speculate that in A. tumefaciens β-1,2-glucan stabilizes membranes, which would be important especially in hypotonic media containing calcium.
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  • 5
    ISSN: 1432-072X
    Keywords: Agrobacterium ; β-1,2-Glucan ; chvB Mutants—Ca2+
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The chvB gene of Agrobacterium tumefaciens encodes a 235 kDa proteinaceous intermediate involved in the synthesis of β-1,2-glucan. chvB mutants show a pleiotropic phenotype. Besides not to produce cyclic β-1,2-glucan, chvB mutants have been reported to be avirulent, attachment-deficient, and nonmotile. In this study we report additional differences from the parent strain, probably all linked to changes in the cell envelope. This pleiotropic phenotype — except for attachment and virulence — could largely be prevented by growing chvB cells with low levels of calcium. Although a role for β-1,2-glucan in osmoadaptation has been proposed, the mode of action of β-1,2-glucan is not known. We speculate that in A. tumefaciens β-1,2-glucan stabilizes membranes, which would be important especially in hypotonic media containing calcium.
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  • 6
    Electronic Resource
    Electronic Resource
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Phytopathology 39 (2001), S. 461-490 
    ISSN: 0066-4286
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Biology
    Notes: Abstract Rhizosphere colonization is one of the first steps in the pathogenesis of soilborne microorganisms. It can also be crucial for the action of microbial inoculants used as biofertilizers, biopesticides, phytostimulators, and bioremediators. Pseudomonas, one of the best root colonizers, is therefore used as a model root colonizer. This review focuses on (a) the temporal-spatial description of root-colonizing bacteria as visualized by confocal laser scanning microscopal analysis of autofluorescent microorganisms, and (b) bacterial genes and traits involved in root colonization. The results show a strong parallel between traits used for the colonization of roots and of animal tissues, indicating the general importance of such a study. Finally, we identify several noteworthy areas for future research.
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  • 7
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Previously, we have shown that the nodE gene is a major determinant of the difference in host range between Rhizobium leguminosarum biovars viciae and trifolii. A new genetic test system for stringent functional analysis of nodE genes was constructed. By testing chimeric nodE genes constructed by the exchange of poiymerase chain reaction (PCR)-generated restriction cassettes, we show that a central domain, containing only 44 non-conserved amino acid residues, determines the host specificity of the NodE protein (401 amino acid residues). Mass spectrometric analysis of the lipo-chitin oligosaccharides (LCOs) produced by the new test strain containing the biovar viciae nodE gene shows that molecules containing a polyunsaturated C18:4 (trans-2. trans-4. trans-6. cis-11-octadecatetraenoic) fatty acyl moiety are produced, as is the case for wild-type R. leguminosarum bv. viciae. The LCOs determined by the biovar trifolii nodE gene, which was overproduced in our test strain, carry C1 8:2 and C18:3 fatty acyl chains containing two or three conjugated trans double bonds, respectively. Therefore, the main difference between the nodE-determined LCOs of biovar viviae and trifolii in this system is the presence or absence of one cis double bond, resulting in the very different hydrophobicity of the LCOs. Using a newly developed spot application assay, we show that the 18:2- and C18:3-containing LCOs are able to induce the formation of nodule primordia on roots of Trifolium pratense. On the basis of these and other recent results, we propose that the host range of nodulation of the R. leguminosarum biovars viciae and trifolii is determined by the degree of hydrophobicity of the poly-unsaturated fatty acyl moieties of their LCOs, which is mediated by the host-specific central domain of the NodE protein.
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  • 8
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Pseudomonas putida strain PCL1445 was isolated from roots of plants, grown on a site polluted with polycyclic aromatic hydrocarbons. PCL1445 produces biosurfactant activity at the end of the exponential growth phase. High-performance liquid chromatography (HPLC) analysis of supernatant extracts of PCL1445 showed two peaks with surface-tension reducing activity, tentatively assigned as biosurfactants putisolvin I and putisolvin II and was followed by structural analyses. A transposon mutant of PCL1445, strain PCL1436, which lacks the two surface-active peaks appeared to be mutated in an open reading frame (ORF) with amino acid homology to various lipopeptide synthetases. Structural analyses of the two biosurfactants of PCL1445 revealed that both are novel cyclic lipodepsipeptides with a hexanoic lipid chain connected to the N-terminus of a 12-amino-acid peptide moiety, in which the C-terminal carboxylic acid group forms an ester with the hydroxyl side-chain of Ser9. The difference between the two structures is located in the second amino acid from the C-terminus, being valine for putisolvin I, and leucine/isoleucine for putisolvin II. We show that these novel compounds lower the surface tension and influence the biofilm development on polyvinyl chloride (PVC). Biofilm formation of the bio-synthetic mutant PCL1436 was strongly increased containing more cells, which formed aggregates earlier as compared with wild-type PCL1445 biofilms. Using purified putisolvin I and II it was shown that biofilm formation of different Pseudomonas strains was inhibited and most interestingly, that both putisolvins are also able to break down existing Pseudomonas biofilms.
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  • 9
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The nodulation genes of rhizobia are involved in the production of the lipo-chitin oligosaccharides (LCO), which are signal molecules required for nodule formation. A mutation in nodZ of Bradyrhizobium japonicum results in the synthesis of nodulation signals lacking the wild-type 2-O-methylfucose residue at the reducing-terminal N-acetylglucosamine. This phenotype is correlated with a defective nodulation of siratro (Macroptilium atropurpureum). Here we show that transfer of nodZ to Rhizobium leguminosarum biovar (bv) viciae, which produces LCOs that are not modified at the reducing-terminal N-acetylglucosamine, results in production of LCOs with a fucosyl residue on C-6 of the reducing-terminal N-acetylglucosamine. This finding, together with in vitro enzymatic assays, indicates that the product of nodZ functions as a fucosyltransferase. The transconjugant R. leguminosarum strain producing fucosylated LCOs acquires the capacity to nodulate M. atropurpureumGlycine sojaVigna unguiculata and Leucaena leucocephala. Therefore, nodZ extends the narrow host range of R. leguminosarum bv. viciae to include various tropical legumes. However, microscopic analysis of nodules induced on siratro shows that these nodules do not contain bacteroids, showing that transfer of nodZ does not allow R. leguminosarum to engage in a nitrogen-fixing symbiosis with this plant.
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  • 10
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Rhizobium loti is a fast-growing Rhizobium species that has been described as a microsymbiont of plants of the genus Lotus. Nodulation studies show that Lotus plants are nodulated by R loti, but not by most other Rhizobium strains, indicating that R. loti produces specific lipo-chitin oligosaccharides (LCOs) which are necessary for the nodulation of Lotus plants. The LCOs produced by five different Rhizobium ioti strains have been purified and were shown to be N-acetylglucosamine pentasaccharides of which the non-reducing residue is N-methylated and N-acylated with c/s-vaccenic acid (C18:1) or stearic acid (C18:O) and carries a carbamoyl group. In one R. loti strain, NZP2037, an additional carbamoyl group is present on the non-reducing terminal residue. The major class of LCO molecules is substituted on the reducing terminal residue with 4-O-acetylfucose. Addition of LCOs to the roots of Lotus plants results in abundant distortion, swelling and branching of the root hairs, whereas spot inoculation leads to the formation of nodule primordia.
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