DNA fragments with genes of and genes of were transferred to exopolysaccharide (EPS)-deficient mutants of the other species. The resulting EPSs were characterized by sensitivity to EPS-dependent bacteriophages, staining with amylovoran-specific fluorescein-isothiocyanate-labelled lectin and chemical techniques, such as determination of the sugar composition and methylation analysis in order to distinguish between amylovoran and stewartan. Degradation by the stewartan-dependent phage ø-K9 was used to detect stewartan production, and staining with a lectin from detected amylovoran capsules. The patterns of sugar linkages were determined by methylation analysis. Stewartan contained a significantly higher glucose to galactose ratio than amylovoran and produced a characteristic signal from 6-linked glucose residues. By these criteria, most mutants displayed exclusively amylovoran synthesis when complemented with the cluster, and mutants complemented with genes produced stewartan. The complementation to an EPS-positive phenotype may require most genes of the or the operon. An exception was an mutant that made predominantly stewartan when complemented with the cosmid. IR spectra showed that both amylovoran and stewartan were acylated when synthesized in but not in The amylovoran-producing merodiploids regained virulence to corn seedlings when mucoidy was restored by the cluster, but the stewartan-producing strains were weakly virulent on pear slices and avirulent on apple seedlings.


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