Abstract
Rhizobium leguminosarum biovars viciae, trifolii, and phaseoli have been grown in the presence and absence of 4',5,7-trihydroxyflavonone (naringenin) or 4',5,7-trihydroxyflavone (apigenin), which induce the expression of nodulation genes of the bacteria. The acidic polysaccharides secreted by the Rhizobium were isolated from the culture media and purified. The polysaccharides were cleaved with a bacteriophage enzyme and the octasaccharide repeating units formed were isolated. The glycosyl sequence and type of nonglycosyl substituents of the repeating units derived from a number of these Rhizobium biovars were shown by fast atom bombardment-mass spectroscopy and proton nuclear magnetic resonance spectroscopy (1H NMR) to be identical. Minor variations in the degree of esterification of the repeating units by O-acetyl and O-(3-hydroxybutanoyl) substituents were observed when the Rhizobium were grown in the presence or absence of the flavonoids. The variation in content and the points of attachment of the O-acetyl and O-(3-hydroxybutanoyl) substituents were as great within each Rhizobium biovar as between different Rhizobium biovars and, contrary to two recent reports (Philip-Hollingsworth, S., Hollingsworth, R. I., and Dazzo, F. B. (1989) J. Biol. Chem. 264, 1461-1466; Philip-Hollingsworth, S., Hollingsworth, R. I., Dazzo, F. B., Djordjevic, M. A., and Rolfe, B. G. (1989) J. Biol. Chem. 264, 5710-5714), the O-acylation patterns were not correlated with the host specificity of the bacteria.
Highlights
Bvs. viciae and trifolii are required for successful nodulation of pea and clover, respectively [10, 11].the function(s) in the symbioses of the acidic polysaccharides secreted by the R. leguminosarum biovars is not understood [12, 13]
The acidic polysaccharides produced by some strains of each of the different biovars of R. leguminosarum,when grown in the absence of host-secreted flavonoids [14], have identical glycosyl sequences but they have the same 0-acyl substituents attached to the same glycosyl residues on the polysaccharide(Fig. 1) and,withinexperimentalerror,the quantity of 0-acyl substituents is the same
RhizobPioulmysaccharide Structures Unrelated to Host Range differ in their glycosyl sequence and/or non-glycosyl substit- riophage [14]. This resulted in completeconversion of the uents and whether there ias correlation between the pattern acidic polysaccharides of all of the R. leguminosarum strains of 0-acylation of the polysaccharides secreted by nod-gene- into their 8-glycosyl residue-repeating units
Summary
This resulted in completeconversion of the uents and whether there ias correlation between the pattern acidic polysaccharides of all of the R. leguminosarum strains of 0-acylation of the polysaccharides secreted by nod-gene- into their 8-glycosyl residue-repeating units. Comparisonofthe0-Acetyland0-(3-Hydroxybutanoyl) Substitution Patternsof the Octaglycosyl Repeating Units Deritied from Various Rhizobium Strains-A previous study established that the pattern of 0-acylation of the polysaccharidesproduced by R.leguminosarum strains grown in the absence of added flavonoid was not the determinant of host specificity [14].
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