No abstract

Species of Microcystis are the most common bloom‐forming cyanobacteria in several countries. Despite extensive studies regarding the production of bioactive cyanopeptides in this genus, there are limited data on isolated strains from Brazil. Three Microcystis sp. strains were isolated from the Salto Grande Reservoir (LTPNA01, 08 and 09) and investigated for the presence of mcy genes, microcystins and other cyanopeptides. Microcystin and microginin production was confirmed in two isolates using high‐resolution tandem mass spectrometry after electrospray ionization (ESI‐Q‐TOF), and the structures of two new microginin congeners were proposed (MG756 Ahda‐Val‐Leu‐Hty‐Tyr and MG770 MeAhda‐Val‐Leu‐Hty‐Tyr). The biosynthesis profile of the identified cyanopeptides was evaluated at different growth phases via a newly developed HPLC‐UV method. Results demonstrated no substantial differences in the production of microcystins and microginins after data normalization to cell quota, suggesting a constitutive biosynthesis. This study represents the first confirmed co‐production of microginins and microcystins in Brazilian strains of Microcystis sp. and highlights the potential of Brazilian cyanobacteria as a source of natural compounds with pharmaceutical interest.

The cosmopolitan and increasing distribution of Cylindrospermopsis raciborskii can be attributed to its ecophysiological plasticity and tolerance to changing environmental factors in water bodies. In reservoirs in the semi-arid region of Brazil, the presence and common dominance of C. raciborskii have been described in waters that are considered hard. We investigated the response of a Brazilian C. raciborskii strain to water hardness by evaluating its growth and saxitoxin production. Based on environmental data, a concentration of 5 mM of different carbonate salts was tested. These conditions affected growth either positively (MgCO3) or negatively (CaCO3 and Na2CO3). As a control for the addition of cations, MgCl2, CaCl2 and NaCl were tested at 5 or 10 mM, and MgCl2 stimulated growth, NaCl slowed but sustained growth, and CaCl2 inhibited growth. Most of the tested treatments increased the saxitoxin (STX) cell quota after six days of exposure. After 12 days, STX production returned to concentrations similar to that of the control, indicating an adaptation to the altered water conditions. In the short term, cell exposure to most of the tested conditions favored STX production over neoSTX production. These results support the noted plasticity of C. raciborskii and highlight its potential to thrive in hard waters. Additionally, the observed relationship between saxitoxin production and water ion concentrations characteristic of the natural environments can be important for understanding toxin content variation in other harmful algae that produce STX.

Cylindrospermopsis raciborskii (Woloszynska) Seenaya & Subba Raju is a freshwater cyanobacterium of worldwide distribution. In the North-eastern region of Brazil many eutrophic water reservoirs are characterized by the dominance of C. raciborskii, with recurrent occurrence of blooms. These water bodies have high conductivity due to a high ionic concentration, and are defined as hard (with high values of CaCO 3 ). In this study, we investigated the long-term effect (12 days) of high calcium concentration (8 mM Ca 2+ ) on C. raciborskii (T3 strain) growth, morphology, toxin content, and metabolism. Changes in protein expression profiles were investigated by proteomic analysis using 2D gel electrophoresis and mass spectrometry. A continued exposure to calcium had a pronounced effect on C. raciborskii (T3): it limited growth, decreased thricome length, increased chlorophyll-a content, altered toxin profile (although did not affect PST content, saxitoxin + neosaxitoxin), and inhibited the expression of proteins related to primary metabolism.

The production of cylindrospermopsin (CYN) by Cylindrospermopsis raciborskii (Woloszynska) Seenaya and Subba Raju (Cyanobacteria) was already shown to be changed by variations in light intensities. Influences of light intensity on CYN production by two different C. raciborskii strains (CYP011K and CYP030A) were studied in batch culture conditions. The strains were grown under photon light intensities from 40 to 348 µmol photons m -2 s -1 . The growth rates were measured by exponential regression of cell number variation along the time. The concentration of chlorophyll-a (Chl-a) was measured by spectrophotometric methods and the CYN concentration was measured by high-performance liquid chromatographic methods. Data from these CYN analyses were evaluated as cell quota (ng CYN 10 -6 cells) or as the relative proportion between toxin concentration and chlorophyll-a concentration (CYN Chl-a -1 ). The CYP011K showed higher growth rates than the CYP030A strains. According to the cell quota results, the production of CYN by these two strains of C. raciborskii is not affected by the intensity of the surrounding light during growth. However, analysis of the relative proportion of CYN Chl-a -1 led to different interpretations, as a negative relation between light intensity and CYN production. Uso da normalização de cylindrospermopsina por quota celular e por clorofila em cepas de Cylindrospermopsis raciborskii sob diferentes intensidades luminosas ResumoA produção de cilindrospermopsina (CYN) por Cylindrospermopsis raciborskii (Woloszynska) Seenaya e Raju Subba já foi associada a mudanças de intensidade luminosa. Neste estudo avaliamos as influências de diferentes intensidades de luz na produção de CYN por duas cepas de C. raciborskii (CYP011K e CYP030A) em cultivos fechados. As cepas foram cultivadas em intensidades luminosas de 40 a 348 µmol fotóns m -2 s -1 . As taxas de crescimento foram medidas por meio de regressão exponencial aplicada à variação do número de células ao longo do tempo. A concentração de clorofila-a (Chl-a) foi medida por métodos espectrofotométricos e a concentração de CYN foi determinada por técnicas de HPLC. Os dados das análises de CYN foram avaliados como quota celular (ng CYN 10 -6 células) ou como proporção relativa entre a concentração de toxina e clorofila-a (CYN Chl-a -1 ). A cepa CYP011K apresentou maiores taxas de crescimento do que a cepa CYP030A. De acordo com os resultados de cota celulares, a produção de CYN por estas duas linhagens de C. raciborskii não é afetada pela intensidade da luz, durante o crescimento. No entanto, a análise da proporção relativa de CYN Chl-a -1 levou a interpretações diferentes, como a aparente relação inversa entre o aumento da intensidade luminosa e a produção de CYN. Este estudo reforça o fato de que diferentes formas de normalização de dados levam a diferentes interpretações sobre a toxicologia fisiologia e ecologia de C. raciborskii.Palavras-chave: Cylindrospermopsis raciborskii, quota celular, cilindrospermopsina por clorofila-a.