Effects of nutrient depletion on the growth and cell concentration of Cylindrospermopsis Raciborskii

Abstract

Eutrophication damages water supply by promoting the proliferation of potentially toxin-producing cyanobacteria. In Ceara State, the abundance of these algae in artificial reservoirs has been reaching up to 95% phytoplankton density of cells. The knowledge of the species growth dynamics depending on the availability of nutrients can promote the understanding of a recurring natural phenomenon, the cyanobacteria blooms. This study aimed to evaluate the influence of macronutrient depletion on the development of C. raciborskii T3 cultures. Experiments were conducted in ASM-1 medium and variations with the removal of 75 and 50% phosphorus and nitrogen from its original composition. Cultures were grown in non-axenic conditions, under constant light of 6.75 μ.mol.m-2.s-1, 12: 12 photoperiod, and at temperature of 24 ± 2ºC. Nitrogen-depleted cultures clearly showed lower growth in comparison with other experiments, reaching the stationary phase earlier, besides lower cell concentrations. Whereas, phosphorus-depleted cultures presented steeper growth curves, similar to the growth registered in the regular ASM-1 medium, and thereby demonstrating that under these experimental conditions, nitrogen was the limiting nutrient for the growth of C. raciborskii.