Phosphate deficiency (N/P 40:1) induces mcyD transcription and microcystin synthesis in Microcystis aeruginosa PCC7806

A real-time RT-PCR analysis of the transcriptional response to phosphate availability of the mcyD gene and microcystin-LR synthesis in Microcystis aeruginosa PCC7806 revealed that no significant changes were observed in the relative quantification of mcyD under excess phosphate (N/P = 1:1), whereas in deficiency of this nutrient (N/P = 40:1), a steady increase of mcyD during the exponential growth phase was detected, showing a maximal level on the 7th day of growth with a 6.8-fold increase over the control cells. The microcystin content in phosphate deficient cells correlates with the trend of mcyD transcription observed. Also, in this work we demonstrate that under phosphate deficiency conditions with a ratio of 40:1 N/P, the growth of M. aeruginosa PCC7806 was not affected when compared to control and phosphate excess samples. When blooms occur, the nutrients become exhausted and therefore phosphate availability will be scarce. In such a complex scenario, microcystin synthesis could be a response to phosphate deficiency, among other stress parameters.

► Effect of phosphate availability on microcystin production was studied.
► Growth rate of Microcystis aeruginosa PCC7806 is not affected under phosphate deficiency (N/P 40:1).
► Real-time RT-PCR shows mcyD transcript increase in phosphate deficient cells (N/P 40:1).
► Intracellular microcystin levels are also increased in phosphate deficient cells.
► Microcystin synthesis could be a stress response to phosphate deficiency.