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Applied and Environmental Microbiology, December 1998, p. 4930-4938, Vol. 64, No. 12
Complex Carbohydrate Research Center,
University of Georgia, Athens, Georgia
30602-4712,1 and
Department of Plant
Pathology, University of Missouri, Columbia, Missouri
652112
Received 3 June 1998/Accepted 6 October 1998
Lipopolysaccharides (LPS) and capsular polysaccharides (K antigens)
may influence the interaction of rhizobia with their specific hosts;
therefore, we conducted a comparative analysis of Sinorhizobium fredii and Sinorhizobium meliloti, which are
genetically related, yet symbiotically distinct, nitrogen-fixing
microsymbionts of legumes. We found that both species typically produce
strain-specific K antigens that consist of
3-deoxy-D-manno-2-octulosonic acid (Kdo), or
other 1-carboxy-2-keto-3-deoxy sugars (such as sialic acid), and
hexoses. The K antigens of each strain are distinguished by glycosyl
composition, anomeric configuration, acetylation, and molecular weight
distribution. One consistent difference between the K antigens of
S. fredii and those of S. meliloti is
the presence of N-acetyl groups in the polysaccharides of
the latter. In contrast to the K antigens, the LPS of
Sinorhizobium spp. are major common antigens. Rough (R) LPS
is the predominant form of LPS produced by cultured cells, and some
strains release almost no detectable smooth (S) LPS upon extraction.
Sinorhizobium spp. are delineated into two major RLPS core
serogroups, which do not correspond to species (i.e., host range). The
O antigens of the SLPS, when present, have similar degrees of
polymerization and appear to be structurally conserved throughout the
genus. Interestingly, one strain was found to be distinct from all
others: S. fredii HH303 produces a unique K antigen,
which contains galacturonic acid and rhamnose, and the RLPS did not
fall into either of the RLPS core serogroups. The results of this study
indicate that the conserved S- and RLPS of Sinorhizobium
spp. lack the structural information necessary to influence host
specificity, whereas the variable K antigens may affect strain-cultivar interactions.
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Sinorhizobium fredii and Sinorhizobium
meliloti Produce Structurally Conserved Lipopolysaccharides and
Strain-Specific K Antigens
*
Corresponding author. Mailing address: Complex
Carbohydrate Research Center, University of Georgia, 220 Riverbend Rd.,
Athens, GA 30602-4712. Phone: (706) 542-1216. Fax: (706) 542-4412. E-mail: breuhs{at}ccrc.uga.edu.
Present address: College of ACES, University of Illinois, Urbana,
IL 61801.
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