Physicochemical studies of extracellular polysaccharides of Erwinia
chrysanthemi spp
Qiong Ding, Michael LaBelle, Byung Yun Yang, Rex Montgomery
*
Department of Biochemistry, College of Medicine, University of Iowa, Iowa City, IA 52242, USA
Received 1 April 2002; revised 20 June 2002; accepted 1 July 2002
Abstract
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
1
H 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 ðR
w
Þ; but
there was a linear relationship of these values and their weight average molecular weight ðM
w
Þ: 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 M
w
and R
w
; but did not seem to be related to the stiffness parameters. The molecular weights of the polysaccharides range from 0.3 to 2.1 £ 10
6
and their hydrodynamic properties are those of polydisperse, polyanionic biopolymers with pseudoplastic, non-thixotropic flow
characteristics in aqueous solutions. q 2003 Elsevier Science Ltd. All rights reserved.
Keywords: Polysaccharide; Erwinia chrysanthemi; Hydrodynamics; Streptomycin-resistant
1. Introduction
Erwinia chrysanthemi are gram-negative bacterial phy-
topathogens (Chatterjee & Starr, 1980; Dickey, 1979;
Dickey, Claflin, & Zumoff, 1987; Dickey, Zumoff, &
Uyemoto, 1984) many of which produce an extracellular
polysaccharide (EPS) when grown on solid media. The
structures of the EPSs produced by E. chrysanthemi pv. zeae
SR260 (Gray, Brand, Koerner, & Montgomery, 1993; Gray,
Koerner, & Montgomery, 1995), a strain pathogenic to corn,
and E. chrysanthemi strains Ech1 and Ech9 (Yang, Gray, &
Montgomery, 1996), strains pathogenic to potato, are
similar, but different from the EPS produced by E.
chrysanthemi Ech6 (Yang, Gray, & Montgomery, 1994),
another strain pathogenic to potato. Evidence is also
presented here showing that the EPS produced by the potato
pathogen, E. chrysanthemi SR80, is similar to EPS of the
strain Ech9.
Two streptomycin-resistant strains (Ech6S þ and
Ech9Sm6) from respective parent strains E. chrysanthemi
Ech6 and Ech9 have been isolated and found to produce
more copious amounts of EPS (Yang, Brand, Gray, &
Montgomery, 2001a), but shown in the present study to have
very similar structures and properties to those from their
parent strains.
2. Methodology
2.1. Analytical and general methods
Methods used for monosaccharide analysis by high-pH
anion-exchange chromatography with pulsed amperometric
detection (HPAEC-PAD) and for 600 MHz
1
HNMR
spectroscopy have been described previously (Yang et al.,
1994).
0144-8617/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved.
PII: S0 1 4 4 - 8 6 1 7 ( 0 2 ) 0 0 1 90 - X
Carbohydrate Polymers 51 (2003) 333–346
www.elsevier.com/locate/carbpol
*
Corresponding author. Tel.: þ1-319-335-7897; fax: þ 1-319-335-9570.
E-mail address: rex-montgomery@uiowa.edu (R. Montgomery).