Physiological and toxicological response of Microcystis aeruginosa BCCUSP232 exposed to Salvinia auriculata extracts.

Microcystis aeruginosa is one of the most predominant freshwater bloom-forming cyanobacterium found globally which is capable of producing toxic secondary metabolites including microcystins that might intoxicate animals and humans when contaminated water or food is ingested. Salvinia auriculata Aubl is one of the plants that might possess bioactive compounds capable of controlling growth and reproduction of M. aeruginosa. The present study aimed to determine the presence of bioactive compounds in S. auriculata extracts and determine alterations occurred in growth and reproduction of M. aeruginosa when exposed to these plant extracts. In addition, this investigation aimed to examine the influence of S. auriculata on antioxidant enzymes detected in M. aeruginosa. The results obtained demonstrated that the aqueous and ethanolic extracts of S. auriculata presented potential for control of cyanobacteria populations, exhibiting algicidal action on M. aeruginosa as well as interfering in antioxidant enzymes activities and parameters associated with oxidative stress. Phytochemical analyses demonstrated the presence of polyphenols and flavonoids content in both extracts. In addition, application of S. auriculata extracts did not produce cytogenotoxicity and/or mutagenicity utilizing Allium cepa test. Therefore, further studies are needed in order to identify and characterize the compounds responsible for these effects on M. aeruginosa and provide information regarding the possible application of S. auriculata in the treatment of drinking water.

Characterization of allelochemicals from Pistia stratiotes extracts and their effects on the growth and physiology of Microcystis aeruginosa.

Due to the public and environmental health impact of cyanotoxins, investigations have been focused on finding environmental friendly algaecides from aquatic plants. The present study had the objective to evaluate the population control and physiological response of Microcystis aeruginosa (Kützing) Kützing (strain BCCUSP232) exposed to Pistia stratiotes L. extracts. Aqueous and ethanolic extracts of P. stratiotes at different concentrations (10, 25, and 50 mg L-1) were submitted to M. aeruginosa and reduced significantly (p<0.05) the cyanobacterium cell density. The ethanolic extract presented the greatest growth inhibition of the strain at the highest concentration. During exposure to P. stratiotes extracts, intracellular hydrogen peroxide levels, malondialdehyde content, and antioxidant enzymes (peroxidase, catalase, and glutathione S-transferase) activities increased in M. aeruginosa, while total protein concentration decreased when compared to the control group. Superoxide dismutase (SOD) activities presented a sharp decline, suggesting superoxide radical and peroxide accumulation. This implied that SOD was a target for bioactive substance(s) from aqueous and ethanolic extracts of P. stratiotes. Phytochemical screening of the extracts revealed that the ethanolic extract presented 93.36 mg gallic acid equivalent (GAE) per gram dry weight (g-1 DW) total polyphenols and 217.33 mg rutin equivalent (RE) per gram dry weight total flavonoids, and for the aqueous extract, 5.19 mg GAE g-1 DW total polyphenols and 11.02 mg RE g-1 DW total flavonoids were detected. Gas chromatography (GC)/mass spectrometry (MS) analyses of the ethanolic and aqueous extracts presented palmitic acid ethyl ester as major allelochemical. In view of these results, it can be concluded that P. stratiotes showed potential in controlling M. aeruginosa populations.