Atividade inibitória de extratos de macrófitas aquáticas sobre crescimento da cianobactéria Raphidiopsis raciborskii

Abstract

Raphidiopsis raciborskii is a species of cyanobacteria with a wide geographic distribution and is often associated with episodes of toxic blooms. Among the alternatives for controlling these blooms, the use of aquatic macrophyte species that exhibit allelopathic activities stands out. Therefore, the present study aimed to investigate the effect of extracts from aquatic plant species on the growth and photosynthetic pigments of the T3 strain of R. raciborskii in bench-scale exposure experiments. The harvesting of plant samples, Myriophyllum aquaticum, Ludwigia cf., Hydrocotyle ranunculoides and Salvinia molesta, was carried out in an artificial lagoon in Barigui Park, Curitiba. After processing the material, the extracts were prepared by maceration using 80% (v/v) hydroethanolic solution as extracting liquid, dried and lyophilized. In growth inhibition experiments, the extracts were solubilized in ASM-1 culture medium at concentrations of 50, 100 and 250 mg L-1 and added to axenic cultures of R. raciborskii at concentrations starting from 8 x 106 cells mL- 1. Cell growth was verified every 24 hours by cell counting and, after 5 days, analyzes of photosynthetic pigments (chlorophyll-a, phycocyanin, phycoerythrin and allophycocyanin) were carried out. The extracts were characterized according to the major secondary metabolite classes. A significant inhibitory effect (p<0.05) was observed for Myriophyllum, Ludwigia and Salvinia at a concentration of 250 mg L-1 and for Myriophyllum and Ludwigia at a concentration of 100 mg L-1. The macrophyte Hydrocotyle did not show a significant inhibitory effect at any of the concentrations tested. All plant species showed positive results for flavonoids, saponins, alkaloids and tannins in qualitative tests. The highest concentrations of polyphenols were obtained for Myriophyllum and Ludwigia, and the highest concentration of flavonoids for Myriophyllum with 15 mgQE L-1. It is concluded that there was a dose-dependent inhibitory allelopathic effect of the species Ludwigia, Myriophyllum and Salvinia on the growth of Raphidiopsis raciborskii. The mechanism of the inhibition may be related to the polyphenolic compounds content in the extracts.