Physicochemical studies of extracellular polysaccharides of Erwinia chrysanthemi spp

The chemical and NMR analysis of the extracellular polysaccharides (EPSs) of several Erwinia chrysanthemi spp gave clear indications of two different families each showing similar structural characteristics. Two EPSs from streptomycin-resistant strains of E. chrysanthemi Ech6 and Ech9, phytopathogen of potatoes, as well as the EPS from the strain SR80, a phytopathogen of maize, have been isolated and purified. Initial structural aspects of these polysaccharides are reflected in the 600 MHz 1D 1H NMR spectra and the high-pH anion-exchange chromatography with pulsed amperometric detection analysis of the complete and partial acid hydrolyzates, which are presented for comparison. The EPS from the strain SR80 is shown to be similar to that from Ech9, and those of the streptomycin-resistant strains are similar to the EPSs of the parent bacteria. Hydrodynamic examinations showed different viscosities and weight average root mean radius (Rw), but there was a linear relationship of these values and their weight average molecular weight (Mw). Within each family, the proposed flexible coil conformations were supported by physical measurements and the stiffness of the coils was greater for the pyruvated molecules in the EPS from Ech6 family. Like many other examples of similar polysaccharides, their pseudoplasticity was most evident in the EPS of higher Mw and Rw, but did not seem to be related to the stiffness parameters. The molecular weights of the polysaccharides range from 0.3 to 2.1×106 and their hydrodynamic properties are those of polydisperse, polyanionic biopolymers with pseudoplastic, non-thixotropic flow characteristics in aqueous solutions.