Diversity of peptides produced by Nodularia spumigena from various geographical regions

Abstract

Cyanobacteria produce a great variety of non-ribosomal peptides. Among these compounds, both acute toxins and potential drug candidates have been reported. The profile of the peptides, as a stable and specific feature of an individual strain, can be used to discriminate cyanobacteria at sub-population levels. In our work, liquid chromatography-tandem mass spectrometry was used to elucidate the structures of non-ribosomal peptides produced by Nodularia spumigena from the Baltic Sea, the coastal waters of southern Australia and Lake Iznik in Turkey. In addition to known structures, 9 new congeners of spumigins, 4 aeruginosins and 12 anabaenopeptins (nodulapeptins) were identified. The production of aeruginosins by N. spumigena was revealed in this work for the first time. The isolates from the Baltic Sea appeared to be the richest source of the peptides; they also showed a higher diversity in peptide profiles. The Australian strains were characterized by similar peptide patterns, but distinct from those represented by the Baltic and Lake Iznik isolates. The results obtained with the application of the peptidomic approach were consistent with the published data on the genetic diversity of the Baltic and Australian populations.

Figure 1

Chemical structure and enhanced ion product mass spectra of spumigin 4 (Hpla + 42)-Hty-Pro-Argal with [M + H] ion at m/z 639 (N. spumigena B15a). The structure was elucidated mainly based on the mass signals at m/z: 621 [M + H − H₂O], 579 [M + H − H₂O − CH₂N₂] or/and [M + H − CH₃COOH], 481 [(Hpla + 42)-Hty-Pro + H], 384 [(Hpla + 42)-Hty + H], 356 [(Hpla + 42)-Hty + H − CO], 250 [AcOCHCO-Hty + H − CO], 239 [Pro-Argal + H − NH₂], 221 [Pro-Argal + H − H₂O − NH₂], 142 [Argal + H − NH₃], 107 [CH₂PhOH], 100 [C₄H₁₀N₃] Argal fragment, 70 Pro-immonium ion.

Figure 2

Chemical structure and enhanced ion product mass spectra of partially identified aeruginosin 21 with [M + H] ion at m/z 587 (N. spumigena KAC66). The mass signals were assigned to the following fragments: 569 [M + H − H₂O], 527 [M + H − H₂O − CH₂N₂], 429 [M + H − Argal], 411 [M + H − Argal − H₂O], 308 [Choi-Argal + H − H₂O − CH₃N₂], 291 [Choi-Argal + H − H₂O − NH₃], 266 [Choi-Argal + H − H₂O − CH₂N₂], 140 Choi-immonium ion, 142 [Argal + H − NH₃]. X—unknown part of the molecule.

Figure 3

Chemical structure and enhanced ion product mass spectra of anabaenopeptin 45 Phe-CO-[Lys-Ile-Hty-MeAla-Phe] with [M + H] ion at m/z 842 (N. spumigena CCNP1401). The mass signals were assigned to the following fragments: 824 [M + H − H₂O], 814 [M + H − CO], 796 [M + H − H₂O − CO], 757 [M + H − MeAla], 729 [M + H − Ile], 677 [M − Phe − 2H], 665 [M + H − Hty], 651 [M + H − (CO-Phe)], 649 cyclo[Lys-Ile-Hty-MeAla-Phe − H], 552 [M + H − (Hty-Ile)], 534 [M + H − (Hty-Ile) − H₂O], 405 [MeAla-Phe-(Lys-CO) + H], 376 [Ile-Hty-MeAla + H], 320 [(Lys-CO-Phe) + H], 263 [MeAla-Hty + H], 231 [MeAla-Phe − H], 114 [MeAla-CO + H], 84 Lys-immonium ion, 58 MeAla-immonium ion.

Figure 4

Chemical structure and enhanced ion product mass spectra of anabaenopeptin 47 Ile-CO-[Lys-Ile-Hty-MeAla-Phe] with [M + H] ion at m/z 808 (N. spumigena NSOR-02). The mass signals were assigned to the following fragments: 790 [M + H − H₂O], 780 [M + H − CO], 762 [M + H − H₂O − CO], 695 [M + H − Ile], 677 [M + H − H₂O − Ile], 651 [M + H − (CO-Ile)], 649 cyclo[Lys-Ile-Hty-MeAsp-Phe − H], 631 [M + H − Hty], 546 [Phe-(Lys-CO-Ile)-Ile + H], 518 [M + H − (Hty-Ile)], 500 [M + H − H₂O − (Hty-Ile)], 417 [Phe-(Lys-CO)-Ile + H], 405 [MeAla-Phe-(Lys-CO) + H], 376 [Ile-Hty-MeAla + H], 361 [MeAla-Lys-Phe + H], 263 [Hty-MeAla + H], 231 [MeAla-Phe − H], 120 Phe-immonium Ion, 107 [CH₂PhOH], 84 Lys-immonium ion, 58 MeAla-immonium ion.

Figure 5

Principal component analysis (PCA) ordination plots (F1 × F2) of Nodularia spumigena strains based on their peptide content as analyzed by LC-MS/MS.