Biochemical characterization of Sinorhizobium meliloti mutants reveals gene products involved in the biosynthesis of the unusual lipid A very-long-chain fatty acid

Andreas F. Haag, Silvia Wehmeier, Artur Muszynski, Bernhard Kerscher, Vivien Fletcher, Susan H. Berry, Georgina L. Hold, Russell W. Carlson, Gail P. Ferguson

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

Sinorhizobium meliloti forms a symbiosis with the legume alfalfa, whereby it differentiates into a nitrogen-fixing bacteroid. The lipid A species of S. meliloti are modified with very-long-chain fatty acids (VLCFAs), which play a central role in bacteroid development. A six-gene cluster was hypothesized to be essential for the biosynthesis of VLCFA-modified lipid A. Previously, two cluster gene products, AcpXL and LpxXL, were found to be essential for S. meliloti lipid A VLCFA biosynthesis. In this paper, we show that the remaining four cluster genes are all involved in lipid A VLCFA biosynthesis. Therefore, we have identified novel gene products involved in the biosynthesis of these unusual lipid modifications. By physiological characterization of the cluster mutant strains, we demonstrate the importance of this gene cluster in the legume symbiosis and for growth in the absence of salt. Bacterial LPS species modified with VLCFAs are substantially less immunogenic than E. coli LPS species, which lack VLCFAs. However, we show that the VLCFA modifications do not suppress the immunogenicity of S. meliloti LPS or affect the ability of S. meliloti to induce fluorescent plant defense molecules within the legume. Since VLCFA-modified lipids are produced by other rhizobia and mammalian pathogens, these findings will also be important in understanding the function and biosynthesis of these unusual fatty acids in diverse bacterial species.
Original languageEnglish
Pages (from-to)17455-17466
Number of pages12
JournalThe Journal of Biological Chemistry
Volume286
Issue number20
Early online date26 Mar 2011
DOIs
Publication statusPublished - 20 May 2011

Keywords

  • bacteria
  • fatty acid
  • lipopolysaccharide (LPS)
  • plant
  • toll-like receptors(TLR)
  • legume
  • sinorhizobium meliloti
  • symbiosis
  • very long-chain fatty acid

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