Skip to main content
ARS Home » Southeast Area » Athens, Georgia » U.S. National Poultry Research Center » Poultry Microbiological Safety & Processing Research » Research » Publications at this Location » Publication #333172

Research Project: Production and Processing Intervention Strategies for Poultry Associated Foodborne Pathogens

Location: Poultry Microbiological Safety & Processing Research

Title: The lipopolysaccharide lipid-a long chain fatty acid is important for rhizobium leguminosarum growth and stress adaptation in free-living and nodule environments

Author
item Bourassa, Dianna
item KANNENBERG, ELMAR - University Of Georgia
item SHERRIER, D - University Of Delaware
item Buhr, Richard - Jeff
item CARLSON, RUSSELL - University Of Georgia

Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/4/2017
Publication Date: 2/1/2017
Citation: Bourassa, D.V., Kannenberg, E.L., Sherrier, D.J., Buhr, R.J., Carlson, R. 2017. The lipopolysaccharide lipid-a long chain fatty acid is important for rhizobium leguminosarum growth and stress adaptation in free-living and nodule environments. Molecular Plant-Microbe Interactions. 30(2):161-175. doi.org/10.1094MPMI-11-16-0230-R.

Interpretive Summary: Rhizobium are bacteria that live in soil and plant environments and are capable of entering into a symbiotic relationship with legume plants by the formation of root nodules. These bacteria convert atmospheric nitrogen into ammonium, which the plant can utilize for protein synthesis, while the plant provides carbohydrates to the bacteria to use as a source of energy. Lipopolysaccharides (LPS) are an important component of the bacterial cell membrane. The LPS of Rhizobium contains a specialized lipid called a very long chain fatty acid (VLCFA). The function of VLCFA for rhizobial growth in soil and plant environments is not well understood. Two genes, acpXL and lpxXL are required for biosynthesis and transfer of VLCFA to the LPS in the bacterial cell membrane. Rhizobium isolates with mutations in these two genes were developed and examined for LPS structure, viability, and symbiosis. The mutations abolished VLCFA attachment to LPS. The acpXL gene mutant transferred a shorter acyl chain instead of VLCFA. The mutant lpxXL strains neither added VLCFA nor a shorter acyl chain. In all Rhizobium strains isolated within symbiotic nodules, the naturally occurring lipids on the LPS had longer acyl chains compared to bacteria not located in symbiotic nodules. Mutant strains displayed altered cell membrane properties, modified cationic peptide sensitivity, and diminished levels of cyclic ß-glucans. During symbiosis, the mutant bacteria nodules were atypically formed, nitrogen fixation was depressed, and early senescence was induced. The role of VLCFA for rhizobial environmental fitness is discussed.

Technical Abstract: Rhizobium bacteria live in soil and plant environments, are capable of inducing symbiotic nodules on legumes, invade these nodules, and develop into bacteroids that fix atmospheric nitrogen into ammonium. Lipopolysaccharide (LPS) is anchored in the bacterial outer membrane through a specialized lipid A containing a very long chain fatty acid (VLCFA). The function of VLCFA for rhizobial growth in soil and plant environments is not well understood. Two genes, acpXL and lpxXL, encoding an acyl carrier protein and an acyltransferase, are required for biosynthesis and transfer of VLCFA to lipid A. Rhizobium leguminosarum mutant strains acpXL, acpXL-/lpxXL-, and lpxXL- were examined for LPS structure, viability, and symbiosis. Mutations in acpXL and lpxXL abolished VLCFA attachment to lipid A. The acpXL mutant transferred a shorter acyl chain instead of VLCFA. Strains without lpxXL neither added VLCFA nor a shorter acyl chain. In all strains isolated from nodule bacteria, lipid A had longer acyl chains compared to laboratory-cultured bacteria, whereas mutant strains displayed altered membrane properties, modified cationic peptide sensitivity, and diminished levels of cyclic ß-glucans. In pea nodules, mutant bacteroids were atypically formed and nitrogen fixation and senescence were affected. The role of VLCFA for rhizobial environmental fitness is discussed.