Atividade inibitória de Myriophyllum aquaticum (Vell.) Verdc. sobre o crescimento de Microcystis aeruginosa Kutzing

Abstract

Microcystis aeruginosa is the one of the species of cyanobacteria that participates in the degradation of water bodies in harmful blooms. Submerged aquatic macrophyte species may present allelopathic strategies for phytoplankton control and, in this context, species of the genus Myriophyllum have shown potential inhibition of cyanobacteria. This study aimed to evaluate the allelopathic activity of Myriophyllum aquaticum on the growth and physiological aspects of Microcystis aeruginosa. The plant material was collected in the rio Verde reservoir (Araucária-PR) and used for the preparation of extracts, using 80% (v / v) hydroethanolic solution and water as extraction liquids. Dried extracts were solubilized in ASM-1 medium and added to flasks containing exponentially growing M. aeruginosa cultures, remaining under monitoring for nine days of exposure. The inhibitory effect was investigated by cellular counting, concentration of photosynthetic pigments (chlorophyll-a, phycocyanin, phycoerythrin and allophycocyanin) and microcystin-LR analysis. With the same experimental protocol, the seasonal analysis of the inhibitory effects was done, using hydroethanolic extraction. The hydroethanolic extracts (EH) of M. aquaticum obtained with autumn collections (2016 and 2017) were fractionated using silica adsorption column chromatography; the fractions obtained were also evaluated for inhibitory activity. The extracts were analyzed for total phenolic content. The allelopathic effect was also evaluated in inhibition experiments using the living plant species (collected and cultivated in the laboratory) inserted in exponential culture of M. aeruginosa, remaining for seven days. The results obtained with the comparative between extracts showed an inhibitory effect on the cell growth for both extracts (aqueous - EA and hydroethanolic - EH), reaching inhibition rates above 91% in the highest concentration tested (250 mg L- 1). However, EH presented greater inhibition at the intermediate concentration (10 mg L-1). In the seasonal comparison, inhibition rates were higher than 94.5% for the four seasons at the highest concentration (100 mg L-1). The levels of photosynthetic pigments and microcystin-LR in general were compatible with the inhibition results. The fractions of autumn, ethyl acetate and methanol showed inhibitory activities, reaching 87,9 and 95,0%, respectively. The EA had a lower yield (8.3%) compared to HD (14.1%). In relation to the total phenolic content, the EHs presented higher concentrations (72,07 mg mL-1) when compared to the aqueous (17,40 mmg mL-1). In the exposure experiments with the live plant, there was 100% inhibition of M. aeruginosa growth in all treatments, as well as effects on photosynthetic pigments and reduction of microcystin-LR concentration. The results obtained demonstrate that M. aquaticum presented allelopathic properties in relation to the growth of M. aeruginosa and the production of microcystin-LR.