Growth of Raphidiopsis raciborskii and Monoraphidium contortum from a subtropical Brazilian Reservoir: interaction, saxitoxin production and response to the trophic state

Abstract

In order to investigate the influence of trophic state from a subtropical reservoir in the state of São Paulo, Brazil, in the competition between the species dominant, Raphidiopsis raciborskii and Monoraphidium contortum, an assay was carried out of interaction between these microorganisms simulating the reservoir in its current conditions, mesotrophic, and another in a supereutrophic condition, as well as detect the production of saxitoxin by cyanobacteria. The experiments were conducted in a climate-controlled room for 15days in triplicate for pure and mixed cultures of each species. Growth curves were developed according to the biovolume-to-biomass and were calculated the growth rates. The saxitoxin synthesis was determined by ELISA. When simulating the mesotrophic and supereutrophic environments, R. raciborskii did not show any differences in its growth and in the saxitoxin production in the interaction with M. contortum, when compared to its control. Concerning M. contortum, your growth was affected in the interactions with cyanobacteria in both trophic state, although the chlorophyceae presented an increasing specific growth rate. The reduction of the growth of M. contortum in interaction with R. raciborskii shows the increase in trophic state can increase the competitiveness of R. raciborskii in the reservoir and to favor your dominance.