Growth and microcystin production of a Brazilian Microcystis aeruginosa strain (LTPNA 02) under different nutrient conditions

Cyanobacteria are prokaryotic and photosynthetic organisms, which can produce a wide range of bioactive compounds with different properties; including a variety of toxic compounds, also known as cyanotoxins. In this work, we describe the isolation of seven cyanobacterial strains from two reservoirs in São Paulo State, Brazil. Seven different chemical variants of microcystins (MC-RR, MC-LR, MC-YR, MC-LF, MC-LW, and two demethylated variants, dm-MC-RR and dm-MC-LR) were detected in three of the ten isolated strains. One particular Microcystis aeruginosa strain (LTPNA 02) was chosen to evaluate its growth by cell count, and its toxin production under seven different nutritional regimes. We observed different growth behaviors in the logarithmic growth period for only three experiments (p < 0.05). The total growth analysis identified four experiments as different from the control (p < 0.01). Three microcystin variants (MC-RR, MC-LR and MC-YR) were quantified by liquid chromatography-tandem mass spectrometry. At the experimental end, the toxin content was unchanged when comparing cell growth in ASM-1 (N:P = 1), MLA and BG-11 (N:P = 10) medium. In all other experiments, the lowest microcystin production was observed from cells grown in Bold 3N medium during the exponential growth phase. The highest microcystin content was observed in cultures using BG-11(N:P = 100) medium.