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Applied and Environmental Microbiology, November 1999, p. 5186-5191, Vol. 65, No. 11
Complex Carbohydrate Research Center,
University of Georgia, Athens, Georgia
30602-4712,1 and Department of
Biosciences, Division of General Microbiology, SF-00014 University
of Helsinki, Finland2
Received 25 January 1999/Accepted 24 August 1999
In two published reports using monoclonal antibodies (MAbs)
generated against whole cells, Olsen et al. showed that strain-specific antigens on the surface of cultured cells of Sinorhizobium
meliloti were diminished or absent in the endophytic cells
(bacteroids) recovered from alfalfa nodules, whereas two common
antigens were not affected by bacterial differentiation (P. Olsen, M. Collins, and W. Rice, Can. J. Microbiol. 38:506-509, 1992; P. Olsen,
S. Wright, M. Collins, and W. Rice, Appl. Environ. Microbiol.
60:654-661, 1994). The nature of the antigens (i.e., the MAb
epitopes), however, were not determined in those studies. For this
report, the epitopes for five of the anti-S. meliloti MAbs
were identified by polyacrylamide gel electrophoresis-immunoblot
analyses of the polysaccharides extracted from S. meliloti
and Sinorhizobium fredii. This showed that the
strain-specific MAbs recognized K antigens, whereas the strain-cross-reactive MAbs recognized the lipopolysaccharide (LPS) core. The MAbs were then used in the analysis of the LPS and K antigens
extracted from S. meliloti bacteroids, which had been recovered from the root nodules of alfalfa, and the results supported the findings of Olsen et al. The size range of the K antigens from
bacteroids of S. meliloti NRG247 on polyacrylamide gels was altered, and the epitope was greatly diminished in abundance compared to those from the cultured cells, and no K antigens were detected in
the S. meliloti NRG185 bacteroid extract. In contrast to
the K antigens, the LPS core appeared to be similar in both cultured cells and bacteroids, although a higher proportion of the LPS fractionated into the organic phase during the phenol-water extraction of the bacteroid polysaccharides. Importantly, immunoblot analysis with
an anti-LPS MAb showed that smooth LPS production was modified in the bacteroids.
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Epitope Identification for a Panel of
Anti-Sinorhizobium meliloti Monoclonal Antibodies and
Application to the Analysis of K Antigens and Lipopolysaccharides
from Bacteroids
*
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.
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