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Journal of Bacteriology, March 2006, p. 2126-2133, Vol. 188, No. 6
0021-9193/06/$08.00+0     doi:10.1128/JB.188.6.2126-2133.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

The Pea Nodule Environment Restores the Ability of a Rhizobium leguminosarum Lipopolysaccharide acpXL Mutant To Add 27-Hydroxyoctacosanoic Acid to Its Lipid A

Complex Carbohydrate Research Center, University of Georgia, 315 Riverbend Road, Athens, Georgia 30602,¹ Department of Plant and Soil Sciences and the Delaware Biotechnology Institute, University of Delaware, Newark, Delaware 19711,² Department of Microbiology and Biotechnology, University of Tübingen, D072076 Tübingen, Germany³

Received 13 October 2005/ Accepted 22 December 2005

Members of the Rhizobiaceae contain 27-hydroxyoctacosanoic acid (27OHC_28:0) in their lipid A. A Rhizobium leguminosarum 3841 acpXL mutant (named here Rlv22) lacking a functional specialized acyl carrier lacked 27OHC_28:0 in its lipid A, had altered growth and physiological properties (e.g., it was unable to grow in the presence of an elevated salt concentration [0.5% NaCl]), and formed irregularly shaped bacteroids, and the synchronous division of this mutant and the host plant-derived symbiosome membrane was disrupted. In spite of these defects, the mutant was able to persist within the root nodule cells and eventually form, albeit inefficiently, nitrogen-fixing bacteroids. This result suggested that while it is in a host root nodule, the mutant may have some mechanism by which it adapts to the loss of 27OHC_28:0 from its lipid A. In order to further define the function of this fatty acyl residue, it was necessary to examine the lipid A isolated from mutant bacteroids. In this report we show that addition of 27OHC_28:0 to the lipid A of Rlv22 lipopolysaccharides is partially restored in Rlv22 acpXL mutant bacteroids. We hypothesize that R. leguminosarum bv. viciae 3841 contains an alternate mechanism (e.g., another acp gene) for the synthesis of 27OHC_28:0, which is activated when the bacteria are in the nodule environment, and that it is this alternative mechanism which functionally replaces acpXL and is responsible for the synthesis of 27OHC_28:0-containing lipid A in the Rlv22 acpXL bacteroids.

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• Forsberg, L. S., Carlson, R. W. (2008). Structural Characterization of the Primary O-antigenic Polysaccharide of the Rhizobium leguminosarum 3841 Lipopolysaccharide and Identification of a New 3-Acetimidoylamino-3-deoxyhexuronic Acid Glycosyl Component: A UNIQUE O-METHYLATED GLYCAN OF UNIFORM SIZE, CONTAINING 6-DEOXY-3-O-METHYL-D-TALOSE, N-ACETYLQUINOVOSAMINE, AND RHIZOAMINURONIC ACID (3-ACETIMIDOYLAMINO-3-DEOXY-D-GLUCO-HEXURONIC ACID). J. Biol. Chem. 283: 16037-16050 [Abstract] [Full Text]