title: Biochemical characterization of Sinorhizobium meliloti mutants reveals gene products involved in the biosynthesis of the unusual lipid A very long-chain fatty acid.
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 Escherichia 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. Because 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.
authors: School of Medicine and Dentistry, Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, United Kingdom.
authors: Andreas F
authors: AF
authors: Haag
authors: Silvia
authors: S
authors: Wehmeier
authors: Artur
authors: A
authors: Muszyński
authors: Bernhard
authors: B
authors: Kerscher
authors: Vivien
authors: V
authors: Fletcher
authors: Susan H
authors: SH
authors: Berry
authors: Georgina L
authors: GL
authors: Hold
authors: Russell W
authors: RW
authors: Carlson
authors: Gail P
authors: GP
authors: Ferguson
mesh_terms: D000213:Acyl Carrier Protein / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D007887:Fabaceae / Q000382:microbiology; D005227:Fatty Acids / Q000096:biosynthesis* / Q000235:genetics; D008050:Lipid A / Q000096:biosynthesis* / Q000235:genetics; D009154:Mutation; D016962:Sinorhizobium meliloti / Q000235:genetics / Q000378:metabolism*; D013559:Symbiosis / Q000502:physiology
chemical_list: D000213:Acyl Carrier Protein; D001426:Bacterial Proteins; D005227:Fatty Acids; D008050:Lipid A