Dados da Tese de Doutorado
Author: Iame Alves Guedes
Títle: Biotic and abiotic factors related to cyanobacterial blooms
Year: 2017. Full text (in Portuguese)
Abstract:
Cyanobacterial blooms occur in freshwater environments around the world, mainly as result of eutrophication. In contrast to abiotic factors, the role of biotic interactions on cyanobacterial bloom dynamics is less explored. Cyanobacterial adaptive advantages are insufficient to explain the prevalence of one species over another in a bloom period, which may be related to specific strategies and interactions with other components of the plankton community. This study aims to evaluate the influence of biotic and abiotic factors on the succession of cyanobacterial species during a bloom. The Funil reservoir was used as model, it is a eutrophic tropical reservoir in which cyanobacterial blooms have been reported over the last 20 years. In the first chapter, we present an integrative view of a mixed cyanobacterial bloom approaching temporal shifts in the dominance of cyanobacteria genera as well as in the associated heterotrophic bacteria community. The major bacteria phyla were Cyanobacteria and Proteobacteria, followed by Actinobacteria, Bacteroidetes, Verrucomicrobia, and Planctomycetes. The first period of the bloom was characterized by high abundances of Microcystis and Bacteroidetes. The second period was dominated by Synechococcus and C. raciborskii, together with Planctomycetes. Both significant positive and negative correlations were observed between certain cyanobacterial and heterotrophic bacteria taxa, pointing to potential ecologically significant associations. In the second chapter, we addressed the population structure of the main cyanobacterial genera involved in the bloom, exploring the intraspecific diversity from 16S rRNA gene sequences. While Microcystis, Pseudanabaena and Cylindrospermopsis were characterized by the dominance of one genotype, Synechococcus and Dolichospermum presented a higher number of sporadic genotypes. Microcystin (MC) and potentially MC producing cells were detected in all samples but no significant correlation between MC and genotypes were found. The results suggest that the populations of these genera are structured in different ways which can be relevant as an adaptation to persist during the bloom. Since in the reservoir phosphorous (P) concentrations are decreasing over the years we investigated the response of the two main cyanobacterial species to P restriction. So, in the third chapter, we tested five strains of C. raciborskii and M. aeruginosa, measuring Growth, photosynthethic efficiency, alkaline phosphatase activity, and maximum uptake rate under phosphorus deprivation. All strains were able to grow, maintain photosynthetic activity, and activate alkaline phosphatase, pointing to their ability to tolerate P deprivation. The level of intraspecific varation precludes generalization and reinforce that the physiological diversity of freshwater cyanobacteria is underscored in studies based in only one or few strains. Altogether, this work highlights the importance of biotic factors in the ecophysiology of cyanobacteria.
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