Data of Thesis
Author: Priscila Rodrigues Koschek
Title:.Interaction between Monoraphidium and Microcystis using medium with released organic matter and mixed cultures
Year: 2008. Full text (in Portuguese)
Abstract
Interspecific communication has an important role in phytoplankton growth and this may be true also for toxin production by cyanobacteria. This group of microorganisms is frequently found as dominant due to eutrophication processes in aquatic environments. Data from Funil Reservoir (Resende-RJ) have demonstrated that at least 90% of phytoplanktonic biomass can be composed of cyanobacteria. Microcystis is one of the main dominant genera. The present study was designed to investigate the interaction between one strain of the chlorophyte Monoraphidium, isolated from that reservoir, and four strains of Microcystis. Cultivation using medium with released organic matter (exudate) from monospecifc cultures and also from mixed cultures, in different proportions, was performed. Mixed cultures included the chlorophyte and one toxic strain of Microcystis (MIRF-01) isolated from the same environment or another nontoxic strain of Microcystis (MICD-01) isolated from a different environment. Physiological conditions of strains were followed by cell counting and by analysis of chlorophyll a. The variation in microcystins production was evaluated by HPLC technique. The results showed that medium with exudates from monospecific cultures of Microcystis did not inhibit growth of Monoraphidium with aeration, except for the 10% concentration exudates, and that occurred in one of the two strains of Microcystis tested. However, in cultivation without aeration the chlorophyte had its growth stimulated by exudate (50%) from one in three Microcystis strains tested. In addition, this stimulatory effect also involved reduction in chlorophyll a. The addition of exudates from Monoraphidium induced growth of one in two Microcystis strains tested, without changes in chlorophyll a. In conditions of mixed cultivation, Monoraphidium as well as Microcystis showed reduced growth as compared to monospecific cultures and the chlorophyte showed increased growth with Microcystis MIRF-01 strain as compared to MICD-01 strain. In the presence of 100% exudate from mixed cultivation inoculated with 70% Monoraphidium and 30% Microcystis the growth of Monoraphidium was inhibited with reduction of chlorophyll a, characterizing chlorosis at the end of cultivation (6 days). For Microcystis, the addition of this same exudate (50%) tended to inhibit cellular growth without affecting chlorophyll a. Microcystins concentration did not change in mixed cultures with Monoraphidium, however it increased using medium with exudates from Monoraphidium monospecific cultures or from mixed cultures in which Monoraphidium predominated. Although the function of microcystins in this interaction is still not clear, this study contributes to enforce the importance of infochemichals for this cyanotoxin production. Therefore, data show that organic matter released by these species varies in relation to growth conditions. Besides, it may have a controlling role in their metabolism at inter-specific and possibly intra-specific level.
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