DNA damages induced by both endotoxin and exotoxin produced by cyanobacteria.

Cyanobacteria are prokaryotes involved in the contamination of aquatic environments since they release toxins that are highly potent and dangerous for living organisms. Prokaryotes produce endo and exotoxins, among others. Exotoxins are highly toxic, while endotoxins have milder toxic effects. The present study evaluated the cytotoxicogenetic potency of both toxins studying them in different concentrations of cyanobacterial biomasses (1 µg/L, 1.5 µg/L, 2 µg/L), to assess the amount of exotoxin present in the cultured medium in which the cyanobacteria were grown. For this evaluation, we used an extract taken from the medium in a concentration of 10%. Our results showed that genotoxic and mutagenic changes in Allium cepa could be observed in all of the varying concentrations of biomass (endotoxin action) and also in the medium induced with exotoxin. Even at low concentrations, these toxins were highly effective at triggering changes in the DNA molecules of organisms exposed to them. This information is highly significant when considering environmental contamination caused by cyanobacteria blooms, since the results of this study show that these toxins may not only kill organisms when found in high concentrations, but also induce mutations when found in low concentrations. Since these mutations are expressed later on in the organisms, it is impossible to associate the observed effect with the event that induced the damage.

Effect of flavonoids isolated from Tridax procumbens on the growth and toxin production of Microcystis aeruginos.

The excessive proliferation of toxin producing cyanobacteria constitutes a significant health risk to the environment and humans. This is due to the contamination of potable water and accumulation of cyanotoxins in plant and animal tissues. As a means of controlling bloom forming cyanobacteria, secondary metabolites with pro-oxidative activities from plants are used to treat water bodies contaminated with cyanobacterial blooms and their associated toxins. The objective of the present study was to evaluate the mechanism of action of extract, fractions and isolated flavonoids of Tridax procumbens L. on Microcystis aeruginosa (Kützing) Kützing. by monitoring changes in growth, oxidative stress, antioxidant response, and cyanatoxin microcystins (MCs) production. The extract, fraction 3 and the isolated flavonoids significantly reduced the cell density of the cyanobacterium. Furthermore, the extract and fraction 3 increased the production of reactive oxygen species, induced lipid peroxidation, and altered antioxidant enzyme activities of M. aeruginosa. The total MCs content of the cyanobacterium was negatively affected by the presence of the extract, fractions and isolated flavonoids. The present study show that T. procumbens has secondary metabolites that are capable of interfering with the physiology and microcystins production of M. aeruginosa. These characteristics are promising for the control of this noxious cyanobacterium in aquatic ecosystems.

Cyanobacterial blooms in stratified and destratified eutrophic reservoirs in semi-arid region of Brazil.

This study investigated the dynamics of cyanobacteria in two deep, eutrophic reservoirs in a semi-arid region of Brazil during periods of stratification and destratification. Four collections were carried out at each reservoir at two depths at three-month intervals. The following abiotic variables were analyzed: water temperature, dissolved oxygen, pH, turbidity, water transparency, total phosphorus, total dissolved phosphorus, orthophosphate and total nitrogen. Phytoplankton density was quantified for the determination of the biomass of cyanobacteria. The data were analyzed using CCA. Higher mean phytoplankton biomass values (29.8 mm(3).L(-1)) occurred in the period of thermal stratification. A greater similarity in the phytoplankton communities also occurred in this period and was related to the development of cyanobacteria, mainly Cylindrospermopsis raciborskii (>3.9 mm(3).L(-1)). During the period of thermal destratification, this species co-dominated the environment with Planktothrix agardhii, Geitlerinema amphibium, Microcystis aeruginosa and Merismopedia tenuissima, as well as with diatoms and phytoflagellates. Environmental instability and competition among algae hindered the establishment of blooms more during the mixture period than during the stratification period. Thermal changes in the water column caused by climatologic events altered other physiochemical conditions of the water, leading to changes in the composition and biomass of the cyanobacterial community in tropical reservoirs.

Cyanobacterial blooms in stratified and destratified eutrophic reservoirs in semi-arid region of Brazil

This study investigated the dynamics of cyanobacteria in two deep, eutrophic reservoirs in a semi-arid region of Brazil during periods of stratification and destratification. Four collections were carried out at each reservoir at two depths at three-month intervals. The following abiotic variables were analyzed: water temperature, dissolved oxygen, pH, turbidity, water transparency, total phosphorus, total dissolved phosphorus, orthophosphate and total nitrogen. Phytoplankton density was quantified for the determination of the biomass of cyanobacteria. The data were analyzed using CCA. Higher mean phytoplankton biomass values (29.8 mm³.L-1) occurred in the period of thermal stratification. A greater similarity in the phytoplankton communities also occurred in this period and was related to the development of cyanobacteria, mainly Cylindrospermopsis raciborskii (>3.9 mm³.L-1). During the period of thermal destratification, this species co-dominated the environment with Planktothrix agardhii, Geitlerinema amphibium, Microcystis aeruginosa and Merismopedia tenuissima, as well as with diatoms and phytoflagellates. Environmental instability and competition among algae hindered the establishment of blooms more during the mixture period than during the stratification period. Thermal changes in the water column caused by climatologic events altered other physiochemical conditions of the water, leading to changes in the composition and biomass of the cyanobacterial community in tropical reservoirs.

Este estudo investigou a dinâmica das cianobactérias em dois reservatórios eutróficos e profundos localizados na região semi-árida do Brasil durante períodos de estratificação e desestratificação térmica. Quatro coletas foram feitas em cada reservatório em duas profundidades em intervalo de três meses. As variáveis abióticas analisadas foram: temperatura da água, oxigênio dissolvido, pH, turbidez, transparência da água, fósforo total, fósforo total dissolvido, ortofosfato e nitrogênio total. A densidade do fitoplâncton foi quantificada para a determinação da biomassa de cianobactérias. Os dados foram analisados usando ACC. Elevados valores médios de biomassa fitoplanctônica (29,8 mm³.L-1) ocorreram no período de estratificação. A maior similaridade das comunidades fitoplanctônicas também ocorreu neste período e foi relacionada ao desenvolvimento de cianobactérias, principalmente Cylindrospermopsis raciborskii (>3,9 mm³ .L-1). Durante o período de desestratificação térmica, esta espécie co-dominou o ambiente com Planktothrix agardhii, Geitlerinema amphibium, Microcystis aeruginosa e Merismopedia tenuissima, bem como com diatomáceas e fitoflagelados. Instabilidade ambiental e competição entre as algas dificultaram o estabelecimento de blooms durante o período de mistura quando comparado com o período de estratificação. Modificações na condição térmica da coluna d'água, causadas por eventos climatológicos, alteraram as demais condições fisicoquímicas da água e ocasionaram mudanças na composição e biomassa da comunidade de cianobactérias em reservatórios tropicais.