Impact of nitrogen and phosphorus on the growth and microcystin-related gene expression of Microcystis aeruginosa PCC 7806

Harmful algal blooms (HABs) have incurred numerous health problems through drinking water or exposure. A better understanding of the growth kinetics and toxin production under different environmental conditions will help develop tools for early-warning indicators for predicting HABs. Lab-scale experiments were performed with Microcystis aeruginosa PCC 7806 under varying N:P ratios and temperatures. We observed different growth behaviors for cultures growing at the three temperatures (20, 25, and 30 degrees C). M. aeruginosa exhibited higher growth rates at higher N:P ratios during the incubation at 25 and 30 degrees C. Microcystis 16S rRNA gene abundance correlated well with the cell growth parameters. Based on RT-qPCR data, the transcripts of mcyA, mcyD, and mcyE were occasionally detected with N:P of 76.86 showing highest detections of all gene transcripts. Intracellular microcystin (MC) production corresponded well with the presence of gene transcripts, while no extracellular MC was detected. These findings would provide valuable insights and beneficial guidance to further explore and predict the impacts of cyanobacterial blooms in freshwater systems.