Avaliação do efeito inibitório de extratos hidroalcoólicos de macrófitas aquáticas sobre o crescimento de Microcystis aeruginosa Kutzing

Abstract

Cyanobacteria proliferate rapidly in eutrophic environments and may be able to synthesize toxins that block water resources use. The cyanobacterium Microcystis aeruginosa is widely distributed, being a potential producer of hepatotoxins called microcystins. The risks to human health of these substances demands methods to control these microorganisms in water. In order to investigate possible inhibitory effects of phytochemical compounds produced by aquatic macrophytes on the growth and microcystin production of Microcystis aeruginosa, the present study used aquatic macrophytes hydroalcoholic extracts of seven species (Eichhornia azurea, Eleocharis cf. Acutangula, Ludwigia cf. peruviana, yriophyllum cf. aquaticum, Pontederia cordata, Sagittaria montevidensis and Typha domingensis). The culture medium ASM-1 was optimized with respect to pH, nitrogen, phosphorus and iron through a factorial design. For extracts preparation, the seven species of aquatic macrophytes were collected, processed and submitted to extraction process solution ethanol 80% (v/v). The extracts were lyophilized and applied in known concentrations to cultures of M. aeruginosa, in optimized ASM-1 medium. Cell concentration was determined every 48 h for 10 days. Statistical differences were evaluated using ANOVA repeated. The microcystinLR concentration was determined in cultures containing greater inhibitory effect extract concentration. Evaluation of bacteriostatic and bactericidal effects at the end of tested period, the cultures were reinoculated into test tubes containing only sterile culture medium. The extracts were evaluated for the presence of secondary metabolites and acute toxicity on Daphnia magna. The experiments showed high growth rates in medium containing higher concentrations of P and Fe. Hydroalcoholic extracts inhibited the growth of Microcystis aeruginosa strain, more effective when applied at a concentration of 500 mg L-1, except for tests performed with S. montevidensis in that the mean inhibitory effect on the cells was the lowest observed. The extract with the highest inhibitory effect was obtained from aerial parts of M. cf. aquaticum in which the inhibition rate was 99.1%. The analyzes showed that microcystin for the extract of E. cf. acutangula the greatest cellular inhibition was accompanied by an increase in microcystin-LR production from 216 to 610 ppb. In tests with S. montevidensis extract the concentration of toxin was few changed, increasing from 216 to 222 ppb. Bactericidal effects were observed for exposure to extracts of E. cf. acutangula, L. cf. peruviana and M. cf. aquaticum. For extracts of E. azurea, P. cordata and T. domingensis toxic effects were not observed. The major toxicity was observed for S. montevidensis, in which 100% of organisms presented immobility in concentration of 50 mg.L-1. Considering inhibition and toxicity data was found that L cf. peruviana extract showed more advantages on its application. The results indicate the possibility of future application of extracts for blooms remediation and also show the need for detailed toxicological and phytochemical investigations in order to identify the active compounds in blooms control and minimize their toxic effects.