Seven new microcystin variants discovered from a native Microcystis aeruginosa strain – unambiguous assignment of product ions by tandem mass spectrometry

Abstract

RATIONALE: High-resolution mass spectrometry was applied to the study of a Microcystis aeruginosa strain previously reported as a [D-Leu 1 ]MC-LR producer. Detailed analysis revealed new microcystin (MC) variants produced from the strain, and seven of these were previously unreported variants. This work shows the importance of mass accuracy for the identification of unknown MCs. METHODS: The M. aeruginosa strain was isolated from a bloom sample collected from Argentina and acclimated to lab conditions. The MC variants in the strain were separated by UV/Vis detection-guided high-performance liquid chromatography, and their structures were unambiguous determined by tandem mass spectrometry (MS/MS). RESULTS: A simple strategy was developed for quickly locating the low-abundance MC precursors from complex samples. MS/MS anlysis revealed ten MC variants produced from the strain, of which seven have never been reported before. CONCLUSIONS: This work shows the interference of isobarics and isomers in the study of unknown MCs, and, therefore, high mass accuracy is important to avoid false assignments. Moreover, the peak list provided here (30-50 fragments unambiguously assigned for ten MCs) can be used as a reference for the discovery of MCs from environmental samples.

Growth, toxin production, active oxygen species and catalase activity of Microcystis aeruginosa (Cyanophyceae) exposed to temperature stress

“…Genome sequencing and characterization of the MC synthetase gene clusters in Microcystis species has elucidated the roles of various mcy genes in the MC biosynthesis pathway (Nishizawa et al, 2000). Our results, as well as those from Qi et al (2015) showed that an isolated strain of M. aeruginosa may produce different structural variants of MCs. It can be explained by the multispecificity of single domains of the MC biosynthesis complex.…”

“…Minor structural changes may have major effects on uptake, organ distribution and excretion of these toxins (Dietrich and Hoeger, 2005). Recently, Qi et al (2015) have shown seven new MC variants in the same strain of Microcystis aeruginosa used for the present study, which has been previously reported as a [D-Leu environmental factors associated with MC production, is necessary to predict toxic events in nature (Hotto et al, 2008).…”

“…It is believed that MCs are released from cyanobacteria after cell lysis, whereas only negligible amounts of toxins are apparently released from healthy cells. Over 70 structural analogues of MC have been identified up to date, but only a few occur frequently at high concentrations (Codd et al, 1999;Qi et al, 2015). Minor structural changes may have major effects on uptake, organ distribution and excretion of these toxins (Dietrich and Hoeger, 2005).…”

Isolation and Characterization of [D-Leu1]microcystin-LY from Microcystis aeruginosa CPCC-464

“…Geographical differences in the distribution of microcystins are being reported [23,24]. Leu 1 -containing MCs have been implicated in bird deaths in both Canada and the USA [6,11] and have been reported in samples from cyanobacterial blooms in Brazil and Argentina [7,25,26] as well as in lichens from Argentina, USA, China, Japan, Norway, Sweden, and Finland [25,27]. Leu 1 variants may be more common and widespread than these studies indicate, as many analyses for MCs are conducted using highly targeted LC-MS/MS methods, and the Leu 1 -containing variants are heavier by 42 Da than the more common (and more commonly targeted) Ala 1 -containing MCs.…”

Determining the Binding Sites of β-Cyclodextrin and Peptides by Electron-Capture Dissociation High Resolution Tandem Mass Spectrometry

“…Samples were ionized using electrospray ionization (ESI) and mass spectra recorded using a 7 Tesla FTICR-MS instrument described elsewhere [26]. For each spectrum, 40-80 individual transients were collected and co-added to enhance S/N [27].…”