title: Identification of microcystins in a Lake Victoria cyanobacterial bloom using LC-MS with thiol derivatization.
abstract: Microcystins are cyclic heptapeptides from cyanobacteria which are responsible for poisonings of livestock and humans. Cyanobacteria also produce a range of peptides and other compounds that can result in complex chromatograms when samples are analysed by LC-MS. Thiol derivatization of the α,β-unsaturated amide present in most microcystins was recently shown to simplify analysis of LC-MS chromatograms of a Microcystis culture, making it easier to identify peaks corresponding to microcystins in complex mixtures. This method was applied to analysis of extracts taken from a natural cyanobacteria bloom in Mwanza Gulf, Lake Victoria, Tanzania, in 2010, revealing the presence of numerous putative microcystin analogues in the sample. Results were verified using LC-MS², LC-MS/MS with precursor-ion scanning, and LC-HRMS, leading to identification of 8 major and 17 minor microcystins in the sample, including analogues of microcystin-RY, -RL and -RA. Microcystin-YR (2), -RR (3), and -RY (9) were isolated from bloom material from Lake Victoria, and the structure of 9 was confirmed by NMR spectroscopic analysis and NMR spectral comparison with 2 and 3. Confirmation of the structure of MC-RY (9) facilitated detailed analysis of its MS² spectrum, thereby supporting the structures of related analogues tentatively established on the basis of MS analyses.
authors.affiliation: Norwegian Veterinary Institute, P.O. Box 750 Sentrum, N-0106 Oslo, Norway. chris.miles@vetinst.no
authors.forename: Christopher O
authors.initials: CO
authors.lastname: Miles
authors.forename: Morten
authors.initials: M
authors.lastname: Sandvik
authors.forename: Hezron E
authors.initials: HE
authors.lastname: Nonga
authors.forename: Thomas
authors.initials: T
authors.lastname: Rundberget
authors.forename: Alistair L
authors.initials: AL
authors.lastname: Wilkins
authors.forename: Frode
authors.initials: F
authors.lastname: Rise
authors.forename: Andreas
authors.initials: A
authors.lastname: Ballot
mesh_terms: D002853:Chromatography, Liquid; D000458:Cyanobacteria / Q000254:growth & development*; D005068:Eutrophication; D060106:Lakes / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D052998:Microcystins / Q000032:analysis*; D013438:Sulfhydryl Compounds / Q000032:analysis*; D053719:Tandem Mass Spectrometry; D013636:Tanzania; D014871:Water Microbiology
chemical_list: D052998:Microcystins; D013438:Sulfhydryl Compounds