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Identification of 3‐hydroxypalmitic acid methyl ester as a novel autoregulator controlling virulence in Ralstonia solanacearum
Author(s) -
Flavier Albert B.,
Clough Steven J.,
Schell Mark A.,
Denny Timothy P.
Publication year - 1997
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.1997.5661945.x
Subject(s) - ralstonia solanacearum , virulence , biology , mutant , biochemistry , extracellular , virulence factor , bacteria , microbiology and biotechnology , escherichia coli , gene , pathogen , genetics
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 co‐ordinately 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 ≤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.