Variations of Growth and Toxin Yield in Cylindrospermopsis raciborskii under Different Phosphorus Concentrations.

The bloom-forming cyanobacteria, , is a producer of the cytotoxic cylindrospermopsin (CYN). In this study, the growth, toxin yield, and expression of CYN biosynthesis genes of were examined under varying phosphorus (P) concentrations. The results show the cell number at 0.00 and 0.01 mg·L P was significantly lower than that at higher P concentrations (≥0.5 mg·L). The chlorophyll content, filament length, heterocyst, and akinete numbers at P ≤ 0.05 mg·L were also significantly reduced. The intracellular and extracellular CYN concentrations and the extracellular proportions increased during the culture period, and larger values were observed at higher P concentrations. Total CYN content reached 45.34-63.83 fg·cell and extracellular CYN proportion reached 11.49%-20.44% at the stationary growth phase. A significantly positive correlation was observed between CYN production and cell growth rate. Three genes were expressed constantly even at P-deficient conditions. The transcription of genes at P-replete conditions or after P supplementation increased from 1.18-fold to 8.33-fold. In conclusion, may rapidly reorganize metabolic processes as an adaptive response to environmental P fluctuations. CYN production and gene expression were constitutive metabolic processes in toxic .