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Chronic Intracellular Infection of Alfalfa Nodules by Sinorhizobium meliloti Requires Correct Lipopolysaccharide Core

Gordon R. O. Campbell, Bradley L. Reuhs and Graham C. Walker
Proceedings of the National Academy of Sciences of the United States of America
Vol. 99, No. 6 (Mar. 19, 2002), pp. 3938-3943
Stable URL: http://www.jstor.org/stable/3058230
Page Count: 6
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Chronic Intracellular Infection of Alfalfa Nodules by Sinorhizobium meliloti Requires Correct Lipopolysaccharide Core
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Abstract

Our analyses of lipopolysaccharide mutants of Sinorhizobium meliloti offer insights into how this bacterium establishes the chronic intracellular infection of plant cells that is necessary for its nitrogen-fixing symbiosis with alfalfa. Derivatives of S. meliloti strain Rm1021 carrying an lpsB mutation are capable of colonizing curled root hairs and forming infection threads in alfalfa in a manner similar to a wild-type strain. However, developmental abnormalities occur in the bacterium and the plant at the stage when the bacteria invade the plant nodule cells. Loss-of-function lpsB mutations, which eliminate a protein of the glycosyltransferase I family, cause striking changes in the carbohydrate core of the lipopolysaccharide, including the absence of uronic acids and a 40-fold relative increase in xylose. We also found that lpsB mutants were sensitive to the cationic peptides melittin, polymyxin B, and poly-L-lysine, in a manner that paralleled that of Brucella abortus lipopolysaccharide mutants. Sensitivity to components of the plant's innate immune system may be part of the reason that this mutant is unable to properly sustain a chronic infection within the cells of its host-plant alfalfa.

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