TY - JOUR
T1 - Biochemical characterization of Sinorhizobium meliloti mutants reveals gene products involved in the biosynthesis of the unusual lipid A very long-chain fatty acid
AU - Haag, Andreas F
AU - Wehmeier, Silvia
AU - Muszyński, Artur
AU - Kerscher, Bernhard
AU - Fletcher, Vivien
AU - Berry, Susan H
AU - Hold, Georgina L
AU - Carlson, Russell W
AU - Ferguson, Gail P
N1 - © 2011 by The American Society for Biochemistry and Molecular Biology, Inc.
PY - 2011/5/20
Y1 - 2011/5/20
N2 - 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.
AB - 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.
KW - Acyl Carrier Protein/genetics
KW - Bacterial Proteins/metabolism
KW - Escherichia coli/genetics
KW - Fabaceae/microbiology
KW - Fatty Acids/biosynthesis
KW - Lipid A/biosynthesis
KW - Mutation
KW - Sinorhizobium meliloti/genetics
KW - Symbiosis/physiology
U2 - 10.1074/jbc.M111.236356
DO - 10.1074/jbc.M111.236356
M3 - Article
C2 - 21454518
SN - 0021-9258
VL - 286
SP - 17455
EP - 17466
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 20
ER -