Cyanobacteria possess the ability to produce compounds with remarkable biological activity, and have thus attracted the
attention of the pharmaceutical industry. Cyanopeptides acting as protease inhibitors have shown potential in the field of pharmacotherapy
through regulation of abnormal physiological processes in the human body. Despite the already described cyanopeptide protease
inhibitors, the search for new congeners is of considerable interest which may pave the way for more efficient molecules. In this study,
the presence of the protease inhibitors aeruginosin and cyanopeptolin with non-, mono- and dichlorination and also genes coding for their
synthetases was investigated in 90 cyanobacterial strains. Mass spectrometry analyses highlighted production of 91, 19 and 3 non-,
mono- and dichlorinated congeners, respectively. The purified extract of Microcystis botrys SPC759 inhibited 61% of pepsin protease.
PCR amplifications of aeruginosin and cyanopeptolin synthetase gene regions were observed in 41 and 28% of evaluated strains,
respectively. The sequences obtained for the aerA-aerB (aeruginosin) and mcnC-mcnE (cyanopeptolin) gene regions grouped together
with their homologues found in other cyanobacterial strains in the phylogenetic analyses with high bootstrap support. Antimicrobial
activity assays performed using all intracellular extracts inhibited 31 and 26% of Gram-negative and Gram-positive pathogenic bacterial
growth, respectively. The results of this study showed the production of aeruginosin and cyanopeptolin and the presence of their genes in
several cyanobacterial genera for the first time besides the discovery of novel congeners.
Keywords: Antimicrobial, aeruginosin, bioactive peptides, chlorination, cyanobacteria, cyanopeptolin, mass spectrometry, natural products, pepsin, protease inhibitors
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