Synergistic allelochemicals from a freshwater

TLDR: This study isolated and structurally characterized these metabolites as cyclicpeptides containing several unusually modified amino acids that are found both in the cells and in the spent media of Oscillatoriasp.

Abstract: The ability of cyanobacteria to produce complex secondary meta-bolites with potent biological activities has gathered considerableattention due to their potential therapeutic and agrochemical ap-plications. However, the precise physiological or ecological rolesplayed by a majority of these metabolites have remained elusive.Several studies have shown that cyanobacteria are able to inter-ferewithotherorganismsintheircommunitiesthroughthereleaseofcompoundsintothesurroundingmedium,aphenomenonusual-ly referred to as allelopathy. Exudates from the freshwater cyano-bacteriumOscillatoriasp. hadpreviously beenshownto inhibitthegreen microalga Chlorella vulgaris. In this study, we observed thatmaximalallelopathicactivityishighestinearlygrowthstagesofthecyanobacterium, and this provided sufficient material for isolationand chemical characterization of active compounds that inhibitedthe growth of C. vulgaris. Using a bioassay-guided approach, weisolated and structurally characterized these metabolites as cyclicpeptides containing several unusually modified amino acids thatare found both in the cells and in the spent media of Oscillatoriasp. cultures. Strikingly, only the mixture of the two most abundantmetabolites in the cells was active toward C. vulgaris. Synergismwasalsoobservedinalungcancercellcytotoxicityassay.Thebinarymixture inhibited other phytoplanktonic organisms, supportinga natural function of this synergistic mixture of metabolites asallelochemicals.