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Applied and Environmental Microbiology, March 2004, p. 1537-1544, Vol. 70, No. 3
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.3.1537-1544.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

2-O-Methylation of Fucosyl Residues of a Rhizobial Lipopolysaccharide Is Increased in Response to Host Exudate and Is Eliminated in a Symbiotically Defective Mutant

K. Dale Noel,* Jodie M. Box, and Valerie J. Bonne

Department of Biological Sciences, Marquette University, Milwaukee, Wisconsin

Received 8 July 2003/ Accepted 1 December 2003

When Rhizobium etli CE3 was grown in the presence of Phaseolus vulgaris seed extracts containing anthocyanins, its lipopolysaccharide (LPS) sugar composition was changed in two ways: greatly decreased content of what is normally the terminal residue of the LPS, di-O-methylfucose, and a doubling of the 2-O-methylation of other fucose residues in the LPS O antigen. R. etli strain CE395 was isolated after Tn5 mutagenesis of strain CE3 by screening for mutant colonies that did not change antigenically in the presence of seed extract. The LPS of this strain completely lacked 2-O-methylfucose, regardless of whether anthocyanins were present during growth. The mutant gave only pseudonodules in association with P. vulgaris. Interpretation of this phenotype was complicated by a second LPS defect exhibited by the mutant: its LPS population had only about 50% of the normal amount of O-antigen-containing LPS (LPS I). The latter defect could be suppressed genetically such that the resulting strain (CE395{alpha}395) synthesized the normal amount of an LPS I that still lacked 2-O-methylfucose residues. Strain CE395{alpha}395 did not elicit pseudonodules but resulted in significantly slower nodule development, fewer nodules, and less nitrogenase activity than lps+ strains. The relative symbiotic deficiency was more severe when seeds were planted and inoculated with bacteria before they germinated. These results support previous conclusions that the relative amount of LPS I on the bacterial surface is crucial in symbiosis, but LPS structural features, such as 2-O-methylation of fucose, also may facilitate symbiotic interactions.

* Corresponding author. Mailing address: Department of Biological Sciences, P.O. Box 1881, Marquette University, Milwaukee, WI 53201. Phone: (414) 288-1475. Fax: (414) 288-7357. E-mail: dale.noel{at}mu.edu.

Applied and Environmental Microbiology, March 2004, p. 1537-1544, Vol. 70, No. 3
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.3.1537-1544.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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