Phytoplankton of the Curonian Lagoon as a New Interesting Source for Bioactive Natural Products. Special Impact on Cyanobacterial Metabolites

Aeruginosin 525 (AER525) from Cyanobacterium Aphanizomenon Sp. (KUCC C2): A New Serine Proteases Inhibitor

Aeruginosins (AERs) are one of the most common classes of cyanobacterial peptides synthesised through a hybrid non-ribosomal peptide synthase/polyketide synthase pathway. They have been found in Microcystis, Nodularia spumigena, Oscillatoria/Plantothrix, and Nostoc. The presence of AER in Aphanizomenon isolated from the Curonian Lagoon was reported for the first time in our previous work. Here, the structure of aeruginosin 525 (AER525), isolated from Aphanizomenon sp. KUCC C2, was characterised based on high-resolution mass spectrometry. This new AER variant shows potent activity against thrombin. It also inhibits trypsin and carboxypeptidase A but has no effect on elastase and chymotrypsin. In terms of the N-terminal residue and biological activity, AER525 displaces some similarity to dysinosins, which belongs to the most potent inhibitors of thrombin among AERs. The findings underline the potential of AER525 as a new anticoagulant agent.

Phylogenetic and molecular characteristics of two Aphanizomenon strains from the Curonian Lagoon, Southeastern Baltic Sea and their biological activities

Polyphasic approach has become a generally accepted method for the classification of cyanobacteria. In this study, we present a detailed characterisation of two strains, KUCC C1 and KUCC C2, isolated from the Curonian Lagoon and classified to the Aphanizomenon genus. Despite phylogenetic similarity, the strains differ with respect to morphology, ultrastructure characteristics, and the metabolite profile. In the KUCC C1 extract, three unknown peptides and eight anabaenopeptins were detected, while KUCC C2 produced one unknown peptide and one aeruginosin. In both strains, a total of eleven pigments were detected. The production of myxoxantophyll, chlorophyll-a, chlorophylide-a, and zeaxanthin was higher in KUCC C2 than in KUCC C1. Extracts from both strains of Aphanizomenon also had different effects in antibacterial, anticancer and enzyme inhibition assays. Comprehensive analyses of Aphanizomenon strains performed in this study showed significant diversity between the isolates from the same bloom sample. These differences should be considered when exploring the ecological significance and biotechnological potential of a given population.

Characterization and Diversity of Microcystins Produced by Cyanobacteria from the Curonian Lagoon (SE Baltic Sea)

Microcystins (MCs) are the most widely distributed and structurally diverse cyanotoxins that can have significant health impacts on living organisms, including humans. The identification of MC variants and their quantification is very important for toxicological assessment. Within this study, we explored the diversity of MCs and their potential producers from the Curonian Lagoon. MC profiles were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) method, while the potential producers were detected based on the presence of genus-specific mcyE gene sequences. Among the numerous MCs detected, one new potential MC variant with m/z 1057 was partially characterized. Moreover, two other MCs with m/z 1075 and m/z 1068 might belong to new variants with serine (Ser), rarely detected in position one of the peptides. They might also represent MC-Y(OMe)R and MC-WR, respectively. However, the application of a low-resolution MS/MS system made the unambiguous identification of the MCs impossible. Based on this example, the problems of peptide structure identification are discussed in the work. Genetic analysis revealed that potential MCs producers include Dolichospermum/Anabaena, Microcystis spp., and Planktothrix agardhii. The diversity and temporal variations in MC profiles may indicate the presence of several chemotypes of cyanobacteria in the Curonian Lagoon.