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.
Highlights
Peptides belong to the most widely studied group of cyanobacterial metabolites
The effectiveness of tandem mass spectrometry in structural elucidation of cyanobacterial peptides has been demonstrated in numerous papers, e.g., [3,4,12,13,14]
The LC-MS/MS method appears to be especially useful in the analysis of small amounts of compounds in complex natural matrices
Summary
Peptides belong to the most widely studied group of cyanobacterial metabolites They are characterized by diverse structures and biological activities [1]. Non-ribosomal peptide synthetases are multifunctional, large enzyme complexes of a modular structure with catalytic domains responsible for the activation (A), thioestrification (T) and condensation (C) of amino acids or short carboxylic acids into peptidyl compounds [9,10]. These compounds have a linear, cyclic or branched-cyclic structure, and are often composed of non-proteogenic or modified proteogenic amino acids [1]. The most frequent modifications in the structure include heterocyclization, epimerization, methylation, acetylation, halogenation or hydroxylation of the units
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