The degree of esterification and points of substitution by O-acetyl and O-(3-hydroxybutanoyl) groups in the acidic extracellular polysaccharides secreted by Rhizobium leguminosarum biovars viciae, trifolii, and phaseoli are not related to host range.

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.