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Effect of ultraviolet radiation (type B) and titaniumdioxide nanoparticles on the interspecific interaction between Microcystis flos-aquae and Pseudokirchneriella subcapitata

Regina Anya Otogo, Mathias Ahii Chia, Ejiroghene Ebelechukwu Uyovbisere, Dora Nguemo Iortsuun, Maria do Carmo Bittencourt-Oliveira
Anthropogenic activities have led to the depletion of the ultraviolet radiation screening ozone layer, exposing aquatic biota to its harmful effects. Also, the rising applications of nanotechnology are resulting in the release and contamination of aquatic ecosystems with engineered nanometals like titanium dioxide nanoparticles (nTiO2). The rise in ultraviolet radiation interacts with nanometals, increasing their bioactivities to susceptible aquatic organisms such as algae and cyanobacteria. The effect of ultraviolet radiation B (UVB) and nTiO2 on Microcystis flos-aquae and Pseudokirchneriella subcapitata during inter-specific interaction was investigated. The specific growth rate (d−1) of M. flos-aquae exposed to nTiO2 increased significantly under monoculture conditions but was suppressed during co-culture with P. subcapitata. Contrarily, UVB stimulated the growth of the cyanobacteriumregardless of the presence or absence of the green microalgae. However, therewas a general decline in the growth of P. subcapitata following cultivation with M. flos-aquae and exposure to UVB and nTiO2. The chlorophyll-a and total chlorophyll content of the monocultures of M. flos-aquae exposed to nTiO2 increased while other co-culture treatments significantly decreased these parameters. The experimental treatments, UVB, nTiO2, and UVB + nTiO2 had differential effects on the pigment content of P. subcapitata. The total protein content, intracellular H2O2, peroxidase (POD), and glutathione S-transferase (GST) activity of both M. flos-aquae and P. subcapitata increased at varying degrees as a function of the treatment condition. Microcystin contentwas highest in co-cultures exposed to UVB. The results of this study suggest that increasing levels of nTiO2 and UVB

Allelopathic interactions between phytoplankton species alter toxin production, oxidative response, and nitrogen fixation

Mathias Ahii Chia, Maria do Carm Bittencourt-Oliveira
Phytoplankton allelopathic studies have mostly been restricted methodologically, leading to very limited quantitative physiological data. In the present study, investigations were carried out to determine physiological changes that occur during allelopathic interactions between chlorophytes (Chlamydomonas reinhardtii P.A. Dangeard 1888; Selenastrum sp.) and cyanobacteria (Microcystis aeruginosa (Ku¨tzing) Ku¨tzing, Microcystis sp. SR, Anabaena variabilis Ku¨tzing ex Bornet & Flahault 1886) using nylon membrane partitioned chambers. The growth of the cyanobacteria and chlorophytes were both stimulated and inhibited in a speciesdependent manner. Among the chlorophytes, the Fv/Fm values of Selenastrum were significantly inhibited by Microcystis LE3 and Anabaena UTEX B377 during co-cultivation. There was a significant change in the Fv/Fm values of Anabaena UTEX B377 during co-cultivation with Chlamydomonas CC-503 and Selenastrum. Total microcystins content of Microcystis LE3 significantly declined during co-cultivation with Chlamydomonas CC-503 and SelenastrumNitrogen fixation by Anabaena UTEX B377 was significantly lowered in the presence of Microcystis LE3, Microcystis SR, Chlamydomonas CC-503, and Selenastrum. Antioxidant enzyme activities of the investigated chlorophytes and cyanobacteria were altered during allelopathic interactions with each other. These results revealed that phytoplankton species undergo various physiological changes during allelopathic interactions.

DNA damages induced by both endotoxin and exotoxin produced by cyanobacteria

Maria Tereza Pamplona-Silva, Letícia Cristina Gonçalves, Maria do Carmo Bittencourt-Oliveira, Maria Aparecida Marin-Morales

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.

The presence of microcystins in the coastal waters of Nigeria, from the Bights of Bonny and Benin, Gulf of Guinea

Medina O Kadiri, Solomon Isagba, Jeffrey U Ogbebor, Osasere A. Omoruyi, Timothy E. Unusiotame-Owolagba, Adriana Sturion Lorenzi, Maria do Carmo Bittencourt-Oliveira, Mathias Ahii Chia

Microcystins (MCs) are the most studied toxins of cyanobacteria in freshwater bodies worldwide. However, they are poorly documented in coastal waters in several parts of the world. In this study, we investigated the composition of cyanobacteria and the presence of microcystins (MCs) in several coastal aquatic ecosystems of Nigeria. Direct morphological analysis revealed that members of the genus Oscillatoria were dominant with five species, followed by Trichodesmium with two species in Nigerian coastal waters. Oso Ibanilo had the highest cyanobacterial biomass (998 × 103 cells/L), followed by Rivers Ocean (156 × 103 cells/L). Except for the Cross River Ocean, cyanobacteria were present in all the investigated aquatic ecosystems. Ten (10) out of twenty water bodies examined had detectable levels of MCs. Furthermore, genomic DNA analysis for the mcyE gene of microcystin synthetase (mcy) cluster showed identities higher than 86% (query coverage > 96%) with toxic strains of cyanobacteria in all the samples analyzed. Also, the sequences of samples matched those of uncultured cyanobacteria from recreational lakes in Southern Germany. Our findings indicate that the presence of toxic cyanobacteria in coastal waters of Nigeria is of public and environmental health concern.

Moringa-Seed-Based Coagulant Removes Microcystins Dissolved in Water

Selma Gouvea-Barros, Maria do Carmo Bittencourt-Oliveira, José E. S. Paterniani

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. 

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

Gustavo Franciscatti Mecinaa, Mathias Ahii Chiae, Micheline Kézia Cordeiro-Araújo, maria do Carmo Bittencourt-Oliveira, Maria Varela Rosa, Ascensión Torres, José Maria Gonzales Molinillo, Francisco Antônio Macías, Regildo Márcio Gonçalves da Silva

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.

The Individual and Combined Effects of the Cyanotoxins, Anatoxin-a and Microcystin-LR, on the Growth, Toxin Production, and Nitrogen Fixation of Prokaryotic and Eukaryotic Algae

Mathias Ahii Chia, Benjamin J. Kramer, Jennifer G. Jankowiak, Maria do Carmo Bittencourt-Oliveira, Christopher J. Gobler

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. 


Willian Rodrigues Macedo, Paulo Roberto de Camago Castro

O tratamento de sementes com agroquímicos é uma prática que confere maior proteção à plântulas contra pragas e doenças, no entanto poucas pesquisas são conduzidas para avaliar o efeito fisiológico desses produtos sobre a cultura do milho. Nosso estudo objetivou determinar o efeito de doses crescentes: 0; 17,5; 35; 52,5 e 70 g ingrediente ativo i.a. de thiamethoxam, via tratamento de sementes, em ambiente controlado e em campo de produção. Observamos que doses crescentes do thiamethoxam alteram o conteúdo de pigmentos foliares fotossinteticamente ativos, nas duas condições experimentais, bem como promoveu o ganho na massa seca da parte aérea das plantas crescidas em casa-de-vegetação, porém não foram observadas diferenças nos índices produtivos em campo de produção. Estes resultados indicam que o produto em questão altera o metabolismo vegetal, porém é necessário confirmar o efeito bioativador na cultura do milho.

Incidence of blossom-end rot in elongated tomato fruit

Lucas Baiochi Riboldi, Sabrina Helena da Cruz Araújo, Sérgio Tonetto de Freitas, Paulo Roberto de Camargo e Castro

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.

The 24-epibrassinolide induces rice tolerance to water stress overcoming losses in grain yield

Lucas Baiochi Riboldi, Julian Alejandro Giraldo Murcia, Sabrina Helena da Cruz Araújo, Paulo Roberto de Camargo e Castro

Water stress leads to large productivity losses in rice cultivation, and plant hormones play a key role in the plant strategies to prevent the harmful effects of water stress in crop development. The objective of this work was to investigate the effects of brassinosteroids (BRs) in rice development and yield under irrigation and under water deficit conditions applied during the preanthesis period. Exogenous applications of bioregulators were performed through leaf spray. Two dosages of 24-epibrassinolide (EBL) were applied (0.01 μM and 0.1 μM), in addition to two dosages of ABA (2.27 mM and 4.54 mM ABA) in order to compare the effects, considering its already known beneficial effects in response to drought adaptation. Plants of the cultivar IRGA 424RI grown under greenhouse conditions were submitted to water deficit from V13 stage until reaching a leaf water potential of -2 MPa. Physiological, growth and biochemical parameters were measured. Even though the water stress reduced plant growth, 0.01µM EBL-treated plants presented unchanged initial dry weight, height and tillering after the stress imposition. The 0.1 µM EBL-treated plants maintained the total dry weight of grains even after water stress imposition, while control and ABA-treated plants showed a 63.9% and 28.1-58.6% reduction, respectively. The 0.01 µM EBL treatment doubled the contents of chlorophyll a, b and total and decreased stomatal conductance under stress in 41.1%. EBL treatments were able to maintain similar peroxidation levels between stressed and non-stressed plants. When analyzed together, these results indicate that EBL shows a promising perspective for improving rice tolerance to controlled water stress.