O tamanho faz diferença? O efeito dos diferentes morfotipos na ecofisiologia da cianobactéria formadora de florações Microcystis aeruginosa

Abstract

The ability of Microcystis aeruginosa to form colonies has been identified as an important characteristic of the species to face environmental adversities, such as protection against predation and the creation by the mucilage of a microenvironment favourable to cells. However, the colony formation and their mechanisms and benefits are not yet fully understood. In this study, the main objective was to contribute to the knowledge of the role of different morphotypes (unicellular and colonial) in the ecophysiology of M. aeruginosa. In the environment, cyanobacterial blooms occur mainly as the colonial form but, due to technical issues, the experiments are traditionally carried out with unicellular cultures. Therefore, we intended to contribute to the development of techniques for cyanobacterial blooms management by using a more realistic environmental approach running experiments with colonial cultures. Our results pointed out that the colonial form of M. aeruginosa promoted an advantage in the protection of the cells against peroxides, so a higher dose application may be necessary for mitigating blooms in which the colonial form is predominant. Furthermore, the peroxide doses capable of causing significant release of microcystins (MC) by the unicellular morphotype did not increase the MC released by the colonial morphotype. Evaluating the effects of antibiotics, the colonial morphotype showed highest resistance to the antibiotic oxytetracycline, while the antibiotic enrofloxacin affected both morphotypes equally. In addition, the unicellular morphotype developed resistance to oxytetracycline more rapidly than the colonial morphotype. In this way, we suggest that the rapid development of antibiotic resistance should be carefully taken into consideration. Finally, when testing the Flock & Sink method, the application of ballast removed significantly the biomass of the colonial morphotype, while the unicellular morphotype required application of ballast and coagulant. The general conclusion of the thesis is that the morphotypes of M. aeruginosa significantly influence the effect of different chemical substances used to control the growth of cyanobacteria. We emphasize that for the management of cyanobacterial blooms is mandatory a thoroughly analysis of the system and of the cyanobacterial community prior to the decision making for an application of mitigation measures.