Acute toxicity of neurotoxin-producing Raphidiopsis (Cylindrospermopsis) raciborskii ITEP-A1 (Cyanobacteria) on the neotropical cladoceran Macrothrix spinosa

Cyanobacterial blooms are recurrent phenomena in several water bodies, mostly eutrophic. They are considered a public health problem, especially considering harmful species like Raphidiopsis raciborskii, a bloom-forming cyanobacteria recorded as a producer of neurotoxic and cytotoxic alkaloids. The present study aimed to assess the acute toxicity of a saxitoxin-producing strain Raphidiopsis raciborskii ITEP-A1 on the zooplankter Macrothrix spinosa. Cladoceran clones isolated from an eutrophic system with cyanobacterial blooms records and an oligotrophic one with no bloom record; both from Pernambuco (Northeastern Brazil), were tested for R. raciborskii ITEP-A1 toxicity. Acute toxicity assays were carried out with newborns (<24h, n=10) and the animals were exposed to three concentrations of cyanobacterial cell biomass (μgC L-1). Quantification of saxitoxins (STX and neoSTX) was done by high-performance liquid chromatography coupled with fluorescence detector (HPLC-RF). The EC50(48h) for the Duas Unas and Prata clones were 359 and 189 μgC L-1, respectively. Obtained results showed that M. spinosa Prata was more sensitive to R. raciborskii than Duas Unas, reinforcing the importance of analyzing the previous life history of the test organisms regarding their native environments. However, both clones demonstrated high sensitivity to R. raciborskii, which enhances their potential for biomonitoring toxic cyanobacterial blooms in tropical reservoirs

Acute toxicity of Microcystis spp. (Cyanobacteria) bloom on Moina minuta (Cladocera) in a tropical reservoir, Northeastern Brazil

Worldwide cyanobacterial blooms have been registered, where harmful species dominance is associated to producing of toxic compounds (cyanotoxins) with adverse effects on several organisms. Acute toxicity of crude extracts from Microcystis bloom occurring in Mundaú reservoir was evaluated by bioassays with the neotropical Cladocera Moina minuta. Samples were taken in the reservoir during the rainy (April/2012) and dry season (September/2012). Cyanobacterial analyses were performed by identification on optical microscopy and direct counting using an inverted microscope. Bloom samples were frozen, lyophilized and re-suspended in deionized water for preparation of extracts. Tests with the cladoceran were carried out in test tubes with different concentrations of the crude extract, diluted in 10 mL reconstituted water. In both rainy and dry periods, densities of Microcystis spp. were above 15x103 ind mL-1. Microcystin concentrations in the extracts were 0.70 (+ 0,009) (rainy season) and 0.69 (+ 0,005) (dry season) μg g-1. The LC50 (48h) of crude extract for both rainy and dry periods was 160 (100 – 255) and 72 (4 – 1113) mg L-1, respectively. These results indicated that extracts of Microcystis spp. were acutely toxic to M. minuta population with suggesting that such events represent potential toxicity to zooplankton

Efeito do balanço pH/carbono inorgânico em parâmetros ecofisiológicos de Cylindrospermopsis raciborskii (Cyanobacteria) sob condições experimentais

Cylindrospermopsis raciborskii (Wolozynska) Seenayya & Subba Raju é uma espécie diazotrófica cosmopolita, potencialmente tóxica e considerada invasora em diferentes latitudes. A capacidade de ocupar diferentes nichos é uma característica que está ligada às suas peculiaridades fisiológicas, as quais permitem que possua uma elevada amplitude ecológica para diferentes variáveis ambientais. No entanto, em condições de cultivo, essa espécie pode apresentar limitações para o crescimento relacionadas ao pH, temperatura e nutrientes. Neste cenário, o presente trabalho objetivou investigar o efeito do pH e fonte de carbono inorgânico em parâmetros relacionados ao crescimento de C. raciborskii. A cepa ITEP-A1 (produtora de saxitoxinas) foi cultivada em meio de cultura ASM-1 e mantida sob condições controladas. O delineamento experimental consistiu do cultivo da linhagem ITEP-A1 em diferentes faixas de pH e disponibilidade de carbono inorgânico, com e sem aeração. Os experimentos foram realizados em erlenmeyers de 2 L com 1,5 L de meio de cultura e foram analisadas curvas e taxas de crescimento, traços morfológicos, aquisição de biomassa, temperatura, pH, condutividade, alcalinidade e carbono inorgânico total dissolvido. Os resultados foram comparados usando ANOVA fatorial com medidas repetidas e ANOVA unifatorial com Teste de Tukey a posteriori, sendo as análises estatísticas e gráficos realizados no programa Statistica 7.0 e R i386 3.1.2, respectivamente. C. raciborskii ITEP-A1 apresentou melhor taxa de crescimento e biomassa sob pH alcalino (>8,0), em ambas condições de aeração. Na condição de pH > 8,0 e com aeração, o íon bicarbonato (HCO3-) foi a principal fonte de carbono inorgânico disponível ao processo fotossintético, o que favoreceu o crescimento de C. raciborskii. Tais resultados podem ser extrapolados para uma escala global, e sugeridos como fatores que têm favorecido a distribuição, bem como expansão dessa cianobactéria para outras latitudes.Cylindrospermopsis raciborskii (Wolozynska) Seenayya & Subba Raju is a cosmopolitan diazotrophic and potentially toxic specie considered as invasive in different latitudes. Its capacity of occupying several niches is a feature which is linked to its physiological traits, which allow it to have wide ecological amplitude to several environmental parameters. However, in laboratory conditions that specie might show some growth limitations related to pH, temperature and nutrients. In this scenario, this work aimed to investigate the effect of pH and source of inorganic carbon in growth-related parameters of C. raciborskii. The strain ITEP-A1 (saxitoxin-producing) was cultured in ASM-1 medium and maintained under controlled conditions. Experiments were worked out in 2L erlenmeyers filled with 1.5 L culture medium in different pH ranges and inorganic carbon availability, with/without CO2 enriched-air bubbling. Cyanobacterial growth, morphological traces, biomass acquisition, temperature, pH, conductivity, alkalinity and total inorganic carbon dissolved were analyzed. Results were compared using repeated-measures ANOVA and ANOVA one way with Tukey’s test post hoc (p 8.0) (P 8.0 with aeration the bicarbonate ion (HCO3-) was the main source of inorganic carbon available to the photosynthetic process, which favored C. raciborskii growth. These results can be extrapolated to a global scale, and suggested as factors that have favored the distribution and expansion of this cyanobacterium to other latitudes.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPE

Saxitoxin-Producing <i>Raphidiopsis raciborskii</i> (Cyanobacteria) Constrains <i>Daphnia</i> Fitness and Feeding Rate despite High Nutritious Food Availability

Changes in food quality can dramatically impair zooplankton fitness, especially in eutrophic water bodies where cyanobacteria are usually predominant. Cyanobacteria are considered a food with low nutritional value, and some species can produce bioactive secondary metabolites reported as toxic to zooplankton. Considering that cyanobacteria can limit the survival, growth and reproduction of zooplankton, we hypothesized that the dietary exposure of neotropical Daphnia species (D. laevis and D. gessneri) to saxitoxin-producing cyanobacteria impairs Daphnia feeding rates and fitness regardless of a high availability of nutritious algae. Life table and grazing assays were conducted with different diets: (1) without nutritional restriction, where neonates were fed with diets at a constant green algae biomass (as a nutritious food source), and an increasing cyanobacterial concentration (toxic and poor food source), and (2) with diets consisting of different proportions of green algae (nutritious) and cyanobacteria (poor food) at a total biomass 1.0 mg C L−1. In general, the presence of high proportions of cyanobacteria promoted a decrease in Daphnia somatic growth, reproduction and the intrinsic rate of population increase (r) in both diets with more pronounced effects in the nutritionally restricted diet (90% R. raciborskii). A two-way ANOVA revealed the significant effects of species/clone and treatments in both assays, with significant interaction between those factors only in the second assay. Regarding the grazing assay, only D. laevis was negatively affected by increased cyanobacterial proportions in the diet. In the life table assay with constant nutritious food, a reduction in the reproduction and the intrinsic rate of the population increase (r) of all species were observed. In conclusion, we found adverse effects of the toxic cyanobacterial strain R. raciborskii on Daphnia fitness, regardless of the constant amount of nutritious food available, proving the toxic effect of R. raciborskii and that the nutritional quality of the food has a greater influence on the fitness of these animals