title: Identification of unsaturated N-acylhomoserine lactones in bacterial isolates of Rhodobacter sphaeroides by liquid chromatography coupled to electrospray ionization-hybrid linear ion trap-Fourier transform ion cyclotron resonance mass spectrometry.
abstract: The identification of two unsaturated N-acylhomoserine lactones (AHLs) produced by Rhodobacter sphaeroides bacteria, based on liquid chromatography (LC) coupled to a hybrid quadrupole linear ion trap (LTQ)-Fourier transform ion cyclotron resonance (FTICR) mass spectrometer upon electrospray ionization (ESI), is presented. Besides the confirmation of the signaling molecule already described in the literature, i.e. (Z)-N-tetradec-7-enoyl-homoserine lactone (C(14:1)-HSL), we have discovered the occurrence, at low, yet significant levels, of another monounsaturated compound, C(12:1) -HSL, which may extend the number of small diffusible chemical signals known for R. sphaeroides. Both unsaturated AHLs were identified by high-resolution FTICR mass spectrometry in extracts of bacterial culture media and the occurrence of a C=C bond was assessed upon their conversion into bromohydrins. Collision-induced dissociation (CID) spectra were then collected on the LTQ mass analyzer. A careful comparison of tandem MS spectra of monounsaturated (i.e., C(12:1)-HSL and C(14:1)-HSL) and saturated AHLs (i.e. C(12)-HSL and C(14)-HSL) led to the emphasis of two series of product ions, exhibiting 14 Da spaced m/z ratios. Both series were referred to progressive fragmentations at the aliphatic end of the AHL acyl chains, followed by neutral losses of terminal alkenes (i.e. CH(2)=CH(CH(2))(n)H). In particular, the series located at the higher end of the explored m/z range (>200 Da), observed only for monounsaturated species, enabled the location of the C=C bond between carbons 7 and 8 of the acyl chain.
authors.affiliation: Dipartimento di Chimica, Università degli Studi di Bari 'Aldo Moro', Campus Universitario, Via E. Orabona 4, 70126 Bari, Italy. tommaso.cataldi@chimica.uniba.it
authors.forename: Tommaso R I
authors.initials: TR
authors.lastname: Cataldi
authors.forename: Giuliana
authors.initials: G
authors.lastname: Bianco
authors.forename: Salvatore
authors.initials: S
authors.lastname: Abate
authors.forename: Ilario
authors.initials: I
authors.lastname: Losito
mesh_terms: D054742:Acyl-Butyrolactones / Q000032:analysis* / Q000737:chemistry*; D000438:Alcohols / Q000737:chemistry; D002853:Chromatography, Liquid / Q000379:methods*; D012242:Rhodobacter sphaeroides / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D053719:Tandem Mass Spectrometry
chemical_list: D054742:Acyl-Butyrolactones; D000438:Alcohols; C023963:bromohydrins