Identification of 3-hydroxypalmitic acid methyl ester as a novel autoregulator controlling virulence in Ralstonia solanacearum

Mol Microbiol. 1997 Oct;26(2):251-9. doi: 10.1046/j.1365-2958.1997.5661945.x.


Expression of virulence genes in Ralstonia solanacearum, a phytopathogenic bacterium, is controlled by a complex regulatory network that integrates multiple signal inputs. Production of several virulence determinants is coordinately reduced by inactivation of phcB, but is restored by growth in the presence of a volatile extracellular factor (VEF) produced by wild-type strains of R. solanacearum. The VEF was purified from spent culture broth by distillation, solvent extraction, and liquid chromatography. Gas chromatography and mass spectroscopy identified 3-hydroxypalmitic acid methyl ester (3-OH PAME) as the major component in the single peak of VEF activity. Authentic 3-OH PAME and the purified VEF were active at < or =1 nM, and had nearly equivalent specific activities for stimulating the expression of eps (the biosynthetic locus for extracellular polysaccharide) in a phcB mutant. Authentic 3-OH PAME also increased the production of three virulence factors by a phcB mutant over 20-fold to wild-type levels, restored normal cell density-associated expression of eps and increased expression of eps when delivered via the vapour phase. Reanalysis of the PhcB amino acid sequence suggested that it is a small-molecule S-adenosylmethionine-dependent methyltransferase, which might catalyse synthesis of 3-OH PAME from a naturally occurring fatty acid. Biologically active concentrations of extracellular 3-OH PAME were detected before the onset of eps expression, suggesting that it is an intercellular signal that autoregulates virulence gene expression in wild-type R. solanacearum. Other than acyl-homoserine lactones, 3-OH PAME is the only endogenous fatty acid derivative shown to be an autoregulator and may be the first example of a new family of compounds that can mediate long-distance intercellular communication.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Gene Expression Regulation, Bacterial*
  • Genes, Bacterial
  • Gram-Negative Aerobic Rods and Cocci / genetics*
  • Gram-Negative Aerobic Rods and Cocci / pathogenicity*
  • Molecular Sequence Data
  • Palmitic Acids*
  • Virulence / genetics


  • Palmitic Acids
  • 3-hydroxypalmitic acid

Associated data

  • GENBANK/U60193