Data of Thesis
Author: Daniel Vinicius Neves de Lima
Title: Responses of Cylindrospermopis raciborskii (Cyanobacteria) strains to water conductivity effect of sodium and magnesium ions
Year: 2017. Full text (in Portuguese)
Abstract:
Semi-arid aquatic environments, such as reservoirs located at the Northeastern region of Brazil, show high water conductivity with values above 1000 μS/cm. This is associated with factors such as the mineral composition of the drainage basin and extreme climate change effects (drought, temperature and precipitation). Previous studies in these environments have shown the occurrence of cyanobacterial blooms with dominance of Cylindrospermopsis raciborskii, a potentially saxitoxin and cylindrospermopsin producer. Studies with laboratory cultivation have investigated the responses of C. raciborskii to abiotic variables such as nutrients, light and temperature, but generally include just one strain. On the other hand, it is well known that blooms consist of a “pool” of strains. Therefore to understand species’ behavior studies with more strains are required. In addition, few studies have evaluated cyanobacterial responses to water conductivity or to the stress caused by different ions (Mg2+, Ca2+, Na+). The aim of the present work was to investigate the effects of water conductivity on saxitoxin-producing and non-producing C. raciborskii strains. Four Brazilian strains were included, two saxitoxin-producers (STX+): ITEP-A1, isolated from Arcoverde reservoir (Northeast, PE), and CyRF-1, isolated from Funil reservoir (Southeast, RJ) - and two non saxitoxin-producers (STX-): CyLP, isolated from Paranoá Lake (Midwast, DF) and NPCS-1 isolated from Custódia reservoir (Northeast, PE). Strains were cultivated in ASM-1 medium and the experimental design consisted of two treatments: NaCl (10mM) and MgCl2 (5mM) addition, resulting in a conductivity of 1500 + 100 μS/cm for both conditions. Control condition was ASM-1 with no salt addition (conductivity of 450 μS/cm). Cultures were maintained at 50 μmol.photon.m2.s-1, dark: light cycle 12 hours, initial pH 8.0 and aeration during 15 days. The physiological responses of the strains were evaluated by the following parameters: growth, photosynthetic parameters, saxitoxin content, protein profiles, intracellular and extracellular carbohydrates. The NaCl treatment did not affect growth of any strain. In contrast, growth in the presence of MgCl2 varied among strains. Thus, the growth response was not related with conductivity alone but with the specific ion in solution. No differences were observed in the protein profiles and the photosynthetic parameters comparing cultures with NaCl or MgCl2 and control. Saxitoxin concentration did not change in these conditions. The production of saxitoxin did not result in advantage or disadvantage for the strains subjected to a higher conductivity. In sum, the treatments resulted in few changes in the physiology of the strains (even comparing STX+ and (STX-). On the other hand, the most evident differences were found in the individual responses of the strains maintained under the same condition. This study reveals the adaptability of C. raciborskii strains to increased conductivity, the differentiated response for each ion and the importance of considering intraspecific variability in studies of the physiology of a cyanobacteria species.
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