Rhizobia are Gram-negative soil bacteria that form nitrogen-fixing symbioses with legumes. A specific rhizobial species recognizes and infects a specific host plant. Rhizobial cell surface lipopolysaccharides (LPSs) are important for endocytotic invasion of host root nodule cells and differentiation into nitrogen-fixing bacteroids within a host-derived intracellular compartment known as the symbiosome. The symbiosome membrane is derived from the Golgi and endoplasmic reticulum of the host cell and is both acidic and low in O2. Rhizobial symbionts are analogous to animal bacterial pathogens that survive in phagosome-derived intracellular compartments and cause chronic infections; e.g. Brucella. The LPSs from members of the Rhizobiaceae have a very long chain lipid-A fatty acid, 27-OHC28:0, (as does the pathogen, Brucella abortus). Also, LPSs from R. etli (Re) (a bean symbiont) and from R. leguminosarum bv. vicae (Rlv) (a pea symbiont) have unique lipid-A, and core oligosaccharide; e.g. they are devoid of phosphate and contain galacturonic acid. During symbiosis, modifications are made to the O-chain polysaccharide (e.g. methylation) and lipid-A. In the case of Rlv, both LPS and the entire bacterium become hydrophobic. This increase in hydrophobicity is due primarily to a doubling of the lipid-A 27-OHC28:0 moiety. It is proposed that the LPS O-chain modifications are required for adherence of the bacterium to the host membrane, and that the 27-OHC28:0 moiety is required to maintain membrane stability during endocytosis and symbiosome formation.
The aims of this proposal are to structurally characterize the O-chain modifications, and to determine the functions of the Re and Rlv unique structural features with regard to both symbiosis and LPS biosynthesis. This will be accomplished through the creation and analysis of Re and Rlv mutants that are specifically altered in these unique structural features (e.g. defective in 27-OHC28:0 incorporation), and by the isolation and characterization of LPS fragments that bind to specific monoclonal antibodies whose LPS epitopes change during symbiosis.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
2R01GM039583-15
Application #
6471935
Study Section
Microbial Physiology and Genetics Subcommittee 2 (MBC)
Program Officer
Chin, Jean
Project Start
1988-06-01
Project End
2006-03-31
Budget Start
2002-04-01
Budget End
2003-03-31
Support Year
15
Fiscal Year
2002
Total Cost
$306,392
Indirect Cost
Name
University of Georgia
Department
Type
Organized Research Units
DUNS #
City
Athens
State
GA
Country
United States
Zip Code
30602
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Brown, Dusty B; Huang, Yu-Chu; Kannenberg, Elmar L et al. (2011) An acpXL mutant of Rhizobium leguminosarum bv. phaseoli lacks 27-hydroxyoctacosanoic acid in its lipid A and is developmentally delayed during symbiotic infection of the determinate nodulating host plant Phaseolus vulgaris. J Bacteriol 193:4766-78
Vanderlinde, Elizabeth M; Harrison, Joe J; Muszy?ski, Artur et al. (2010) Identification of a novel ABC transporter required for desiccation tolerance, and biofilm formation in Rhizobium leguminosarum bv. viciae 3841. FEMS Microbiol Ecol 71:327-40
Vanderlinde, Elizabeth M; Muszynski, Artur; Harrison, Joe J et al. (2009) Rhizobium leguminosarum biovar viciae 3841, deficient in 27-hydroxyoctacosanoate-modified lipopolysaccharide, is impaired in desiccation tolerance, biofilm formation and motility. Microbiology 155:3055-69
Forsberg, L Scott; Carlson, Russell 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 s J Biol Chem 283:16037-50
D'Haeze, Wim; Leoff, Christine; Freshour, Glenn et al. (2007) Rhizobium etli CE3 bacteroid lipopolysaccharides are structurally similar but not identical to those produced by cultured CE3 bacteria. J Biol Chem 282:17101-13

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