title: Profiling of ornithine lipids in bacterial extracts of Rhodobacter sphaeroides by reversed-phase liquid chromatography with electrospray ionization and multistage mass spectrometry (RPLC-ESI-MS(n)).
abstract: Ornithine lipids (OLs), a sub-group of the large (and of emerging interest) family of lipoamino acids of bacterial origin, contain a 3-hydroxy fatty acyl chain linked via an amide bond to the α-amino group of ornithine and via an ester bond to a second fatty acyl chain. OLs in extracts of Rhodobacter sphaeroides (R. sphaeroides) were investigated by high-performance reversed phase liquid chromatography (RPLC) with electrospray ionization mass spectrometry (ESI-MS) in negative ion mode using a linear ion trap (LIT). The presence of OLs bearing both saturated (i.e, 16:0, 17:0, 18:0, 19:0 and 20:0) and unsaturated chains (i.e., 18:1, 19:1, 19:2 and 20:1) was ascertained and their identification, even for isomeric, low abundance and partially co-eluting species, was achieved by low-energy collision induced dissociation (CID) multistage mass spectrometry (MS(n), n = 2-4). OLs signatures found in two R. sphaeroides strains, i.e., wild type 2.4.1 and mutant R26, were examined and up to 16 and 17 different OL species were successfully identified, respectively. OLs in both bacterial strains were characterized by several combinations of fatty chains on ester-linked and amide-linked 3-OH fatty acids. Multistage MS spectra of monoenoic amide-linked 3-OH acyl chains, allowed the identification of positional isomer of OL containing 18:1 (i.e. 9-octadecenoic) and 20:1 (i.e. 11-eicosenoic) fatty acids. The most abundant OL ([M-H](-) at m/z 717.5) in R. sphaeroides R26 was identified as OL 3-OH 20:1/19:1 (i.e., 3-OH-eicosenoic acid amide-linked to ornithine and esterified to a nonadecenoic chain containing a cyclopropane ring). An unusual OL (m/z 689.5 for the [M-H](-) ion), most likely containing a cyclopropene ester-linked acyl chain (i.e., OL 3-OH 18:0/19:2), was retrieved only in the carotenoidless mutant strain R26. Based on the biosynthetic pathways already known for cyclopropa(e)ne ring-including acyl chains, a plausible explanation was invoked for the enzymatic generation of this ester-linked chain in R. sphaeroides.
authors.affiliation: Dipartimento di Chimica, Università degli Studi Aldo Moro di Bari, Via E. Orabona, 4 - 70126 Bari, Italy.
authors.forename: Sara
authors.initials: S
authors.lastname: Granafei
authors.affiliation: Dipartimento di Chimica, Università degli Studi Aldo Moro di Bari, Via E. Orabona, 4 - 70126 Bari, Italy; Centro Interdipartimentale SMART, Università degli Studi Aldo Moro di Bari, Via E. Orabona, 4 - 70126 Bari, Italy.
authors.forename: Ilario
authors.initials: I
authors.lastname: Losito
authors.affiliation: Istituto Processi Chimico Fisici CNR, Università degli Studi Aldo Moro di Bari, Via E. Orabona, 4 - 70126 Bari, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Trotta
authors.affiliation: Istituto Processi Chimico Fisici CNR, Università degli Studi Aldo Moro di Bari, Via E. Orabona, 4 - 70126 Bari, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Italiano
authors.affiliation: Istituto Processi Chimico Fisici CNR, Università degli Studi Aldo Moro di Bari, Via E. Orabona, 4 - 70126 Bari, Italy.
authors.forename: Vincenzo
authors.initials: V
authors.lastname: de Leo
authors.affiliation: Istituto Processi Chimico Fisici CNR, Università degli Studi Aldo Moro di Bari, Via E. Orabona, 4 - 70126 Bari, Italy.
authors.forename: Angela
authors.initials: A
authors.lastname: Agostiano
authors.affiliation: Dipartimento di Chimica, Università degli Studi Aldo Moro di Bari, Via E. Orabona, 4 - 70126 Bari, Italy; Centro Interdipartimentale SMART, Università degli Studi Aldo Moro di Bari, Via E. Orabona, 4 - 70126 Bari, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Palmisano
authors.affiliation: Dipartimento di Chimica, Università degli Studi Aldo Moro di Bari, Via E. Orabona, 4 - 70126 Bari, Italy; Centro Interdipartimentale SMART, Università degli Studi Aldo Moro di Bari, Via E. Orabona, 4 - 70126 Bari, Italy. Electronic address: tommaso.cataldi@uniba.it.
authors.forename: Tommaso R I
authors.initials: TR
authors.lastname: Cataldi
mesh_terms: D056148:Chromatography, Reverse-Phase / Q000379:methods*; D008055:Lipids / Q000032:analysis*; D009952:Ornithine / Q000032:analysis*; D012242:Rhodobacter sphaeroides / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
chemical_list: D008055:Lipids; D009952:Ornithine
keywords: Lipoamino acids; Liquid chromatography; Monounsaturated fatty acids; Ornithine lipids; Rhodobacter sphaeroides; Tandem MS