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Data of Thesis

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Author: Ana Cláudia Pimentel de Oliveira.

Title: Ecophysiological studies of Synechocystis aquatilis f. aquatilis (Cyanophyceae)and microcystin production in unialgal and mixed cultures

Year: 1997.    Full text (in Portuguese)

Abstract

Biological activity of secondary metabolites produced by cyanobacteria have been studied due to their importance in biotechnology and/or pharmacology. These metabolites have a wide spectrum of activity: while: allelopathic, algicidal; antibacterial, antifungal, antineoplastic, cytotoxic, antiviral, enzyme inhibitors and inflammatory. Biotechnological potential of polar extracts of some strains of cyanobacteria (Oscillatoriales) of Brazilian water bodies were evaluated through the following biological tests: diffusion tests, platelet aggregation, antiviral and cytotoxic activity. In diffusion tests, the better results were with MeOH 80% (N) extracts of the strains NPCD-2 (Limnothrix sp), NPDF-2 (Leptolyngbya sp) and NPBT-l (Tychonema sp) strains against Candida albicans. However the extract lost activity when the strains were subcultured for long periods, probably due to a decreased production of the bioactive metabolite. In the platelet aggregation tests, the extracts (N) and (I) of NPFX -1 - Leptolyngbya sp (MeOH 20%), NPFE-l - Tychonema sp (MeOH 20%) and NPCD-2- Limnothrix sp (H20) strains, were able to induce a natural platelet aggregation in the absence of the agonists ADP and P AF. This result suggests indirectly a potential inflammatory activity of these extracts. Nevertheless antiviral tests showed no activity against HSV -1 (Herpes simplex virus - type 1). Cytotoxic tests showed that the aqueous extracts of NPRG-l, NPDF-2 and NPRE-3 strains, both Leptolyngbya sp (Pseudoanabaenaceae) genera, can provide important information to developed new anti-cancer drugs. These results confirm the potential of extracts of cyanobacteria from the order Oscillatoriales as a promising source of new bioactive metabolites and could provide subsidy to future investigations chemical and biotechnological. The occurrence of toxic 'blooms' of Cyanophyceae in eutrophic lakes, rivers and reservoirs has been frequent. Cyanophyceae toxins may cause poisoning of mammals, birds, fishes and several effects in public health. Hepatotoxins are the most common toxins produced by cyanophyceae and have been receiving more attention due to their biological activity and wide distribution. Nevertheless, the controlling mechanisms of cyanotoxins production has not been fully understood yet, although there are already some evidences of dependency on nutritional factors for the stimulation of growth and synthesis of these hepatotoxins. Previous studies with the strain NPBS-2 of Synechocystis aquatilis f aquatilis have shown that this strain presented a high degree of hepatotoxicity when grown in mixed cultures with the Chlorophyceae Monorraphydium convolutum. Due to this fact, experiments with unialgal and mixed cultures were carried out with both species with the aim of understanding which are the likely factors that would be stimulating the production of microcystins by Synechocystis aquatilis f. aquatilis. The cultures of both species were carried out in ASM-I and Z-8 standard media and in modified 'Special' and 'Reconstituted' media which have the nutritional composition modified from ASM-I and Z-8 media respectively. During the experiments, we followed the physiological state of the cultures by cell counting and by analysis of chlorophyll-a, intra and extracellular carbohydrates and protein. The variation in microcystin production was evaluated by mouse bioassay, immunoassay and High Performance Liquid Chromatography (HPLC). The cultures carried out in Z-8 medium, which is three times more concentrated in nitrate than ASM-l medium, showed a good cellular growth. However, in this culture medium, cells grown in unialgal and mixed conditions have shown no toxicity. Nevertheless, the mixed cultures carried out in ASM-I medium showed high toxicity. The chemical composition of the culture media significantly affected the growth of both species in unialgal and mixed cultures. Microcystins production also varied under these different culture conditions. The chromatograms obtained by HPLC showed that S. aquatilis f aquatilis grown in different proportions of M. COI1VO/utlln7 presented a variation in both quality and quantity of microcystins production. Therefore, one must consider that besides the physical and chemical factors already determined in other studies, the cellular growth of cyanophyceae and microcystins production by these organisms may be affected by biological factors related to interspecific interactions.

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