Artigos

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.

Toxic cyanobacterial blooms commonly occur in bodies of water used to supply drinking water, leading to the presence of high concentrations of toxins in the water. Among the cyanotoxins, microcystins are the most frequently encountered in aquatic ecosystems. They have been associated with animal and human intoxication, illness, and death. Most of the chemical and physical methods employed by water control managers to control cyanobacteria and cyanotoxins are neither cost effective nor efficient. As an alternative, using natural coagulants that are biodegradable and easily deployed for water purification in small human communities have been proposed. In the present study, 28 assays are carried out using the jar test to investigate the effect of stirring rotation (time and speed), pH, and aqueous extracts of Moringa oleifera L. seeds (AqMO) on the cells, turbidity, and removal of Microcystis aeruginosa cells and extracellular microcystins. Cell removal efficiency ranged from 22.6  1.3 to 85.8  0.6%, and the reduction in turbidity ranged from 14.0  3.1 to 87.4  0.3% as a function of the different treatments. According to the critical value predicted, an AqMO dose of 540 mg L1 combined with an initial cell density of 10 105 cells mL1 will completely remove M. aeruginosa cells and significantly decrease extracellular microcystins content (ca. 54.4  7.9%). These results show promise for the development of effective treatments of potable water contaminated with cyanobacteria and microcystins in rural and isolated areas, thereby reducing the public health risks associated with these organisms. 

Globally, eutrophication and warming of aquatic ecosystems has increased the frequency and intensity of cyanobacterial blooms and their associated toxins, with the simultaneous detection of multiple cyanotoxins often occurring. Despite the co-occurrence of cyanotoxins such as microcystins and anatoxin-a (ATX) in water bodies, their effects on phytoplankton communities are poorly understood. The individual and combined effects of microcystin-LR (MC-LR) and ATX on the cyanobacteria Microcystis spp., and Anabaena variabilis (a.k.a. Trichormus variabilis), and the chlorophyte, Selenastrum capricornutum were investigated in the present study. Cell density, chlorophyll-a content, and the maximum quantum efficiency of photosystem II (Fv/Fm) of Microcystis cells were generally lowered after exposure to ATX or MC-LR, while the combined treatment with MC-LR and ATX synergistically reduced the chlorophyll-a concentration of Microcystis strain LE-3. Intracellular levels of microcystin in Microcystis LE-3 significantly increased following exposure to MC-LR + ATX. The maximum quantum efficiency of photosystem II of Anabaena strain UTEX B377 declined during exposure to the cyanotoxins. Nitrogen fixation by Anabaena UTEX B377 was significantly inhibited by exposure to ATX, but was unaffected by MC-LR. In contrast, the combination of both cyanotoxins (MC-LR + ATX) caused a synergistic increase in the growth of S. capricornutum. While the toxins caused an increase in the activity of enzymes that scavenge reactive oxygen species in cyanobacteria, enzyme activity was unchanged or decreased in S. capricornutum. Collectively this study demonstrates that MC-LR and ATX can selectively promote and inhibit the growth and performance of green algae and cyanobacteria, respectively, and that the combined effect of these cyanotoxins was often more intense than their individual effects on some strains. This suggests that the release of multiple cyanotoxins in aquatic ecosystems, following the collapse of blooms, may influence the succession of plankton communities. 

Blossom-end rot (BER) is a physiological disorder that can affect 100% of the fruit crop depending on the genotype. Tomato varieties with elongated fruit usually have a greater susceptibility to BER than other varieties. To evaluate and identify the possible physiological and morphological characteristics related to the onset of BER development, four varieties of long-shape tomato fruit with different susceptibility to BER: ‘San Marzano,’ ‘Banana Legs,’ ‘Roma,’ and ‘Mini-Roma’ were examined. Our results show that ‘San Marzano’ and ‘Banana Legs’ (elongated fruit) had a higher incidence of BER and lower Ca²⁺ concentration in the distal fruit tissue. ‘San Marzano’ (the most elongated fruit) presented higher electrolyte leakage in the distal fruit tissue. By comparison, ‘Roma’ and ‘Mini-Roma’ (less elongated fruit) were less susceptible to BER and had a higher ratio for proximal/distal fruit Ca²⁺ and a lower distal cell-wall bound content of Ca²⁺. Additionally, xylem functionality (vessels transporting water and solutes) in the distal fruit tissue was also higher in these more-tolerant varieties. These results support the theory that total fruit content of Ca²⁺ is not the only factor determining fruit susceptibility to BER, but rather a balance between physiological and morphological factors that influence Ca²⁺ transport and allocation in the fruit.