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Data of Thesis

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Author: Débora Guerreiro Aguiar.

Title: Effect of different nutrient concentration on growth and toxin production by Microcystis aeruginosa Kütz Emend. Elenkin (Cyanophyceae) in culture conditions.

Year: 1995.    Full text (in Portuguese)

Abstract

The increase of eutrophication of Brazilian natural freshwater supplies and reservoirs has led to Cyanophyta species becoming dominant. The most common Cyanophyta genera producing "blooms" on the surface of eutrophic Brazilian water bodies is Microcystis and the hepatotoxin production by strains of this genera has been showed in many areas of the world In order to understand the relationship between nutrient concentration and hepatotoxin production, a hepatotoxic strain (NPJB- l) of Microcystis aeruginosa, isolated from Lagoa das Garças (São Paulo city - Brazil) was cultivated in ASM-l medium using different concentrations of the nutrients (N/20, N/10, N/5, ASM-l (C), 2N, 2NP, 5N, 5NP, ASM-l/2, 2ASM-l and 5ASM-l) at 22uE om-2 o S-1 of light with a photoperiod of 12 h and 2l±2°C of temperature. The culture growth was monitored by cell count, growth rates, biomass production and cell productivity, Cells growing on the exponential lyophilized phase were harvested, for mouse bioassays and concentrated and toxin extraction o isolation, purification and quantification of the toxins were carried out by reverse phase HPLC o The growth rate was reduced in the conditions 2N, 5N and ASM-l/2 and it was increased under 2ASM-l and 5ASM- l conditions. The cell biomass and cell productivity were increased in the conditions 2ASM- l and 5ASM- lo Cell productivity was reduced under N/20, N/10, N/5 and ASM- l/2 conditions. This Microcystis s aeruginosa strain (NPJB-l) produces two different hepatotoxic heptapeptide microcystins: LR and LF, however the decrease of hepatotoxicity under the conditions ASM-l/2 and 2ASM-l was mainly related with the decrease of microcystin- LR production. The best culture condition for the growth of this strain was not coincident with the condition where was observed the maximum hepatotoxins production. Therefore the increase of nutrient concentration in aquatic environment should not be directly related with the hepatotoxin production by the Microcystis strains.

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