Influência de fatores bióticos e abióticos na composição de metabólitos secundários em cianobactérias

Abstract

Cyanobacteria are known to produce different bioactive peptides. The most common are microcystins, cyanopeptolins, anabaenopeptins and microviridins. The hypotheses about the functions of these metabolites include protection against grazing, allelophatic effects, quorum sensing and internal metabolism, but some of these functions might be only of secondary importance. The comprehension of the factors affecting the production of these compounds may give some clues about its ecological and physiological functions. In this study, the influence of different factors (light, iron concentration and zooplankton extracts) on the pattern of peptides in cyanobacteria was tested. The experiments were done with two strains of Radiocystis fernandoii (light and zooplankton experiments) one strain of Planktothrix agardhii (iron experiments) and one strain of Microcystis panniformis (zooplankton experiments). All the experiments were done in triplicates under controlled growth conditions with the variation of a single factor. At the end of the experimental time, cultures were freeze dried and the peptides extracted with methanol 75% and purified with C18 SPE cartridges. The peptides were quantified by HPLC and the main peaks were analyzed in a mass spectrometer. The results showed that the peptide pattern is influenced by different light intensities and iron concentration, while the zooplankton extracts had almost no influence. These results may indicate that the toxic function of these compounds might be secondary. It was possible to see that the peptide concentration is not necessarily higher when the growth conditions are better. It is also important to note that it is necessary to consider the whole array of peptides produced by a strain or species in order to study the relationship between these compounds, its ecological and physiological functions and the environmental factors.