Potassium regulates the growth and toxin biosynthesis of Microcystis aeruginosa

Potassium (K+) is the most abundant cation in phytoplankton cells, but its impact on Microcystis aeruginosa (M. aeruginosa) has not been fully documented. This study presents evidence of how K+ availability affects the growth, oxidative stress and microcystin (MC) production of M. aeruginosa. The iTRAQbased proteomic analysis revealed that during K+ deficiency, serious oxidative damage occurred and the photosynthesis-associated and ABC transporter-related proteins in M. aeruginosa were substantially downregulated. In the absence of K+, a 69.26% reduction in cell density was shown, and both the photosynthesis and iron uptake were depressed, which triggered a declined production of ATP and expression of MC synthetases genes (mcyA, B and D), and MC exporters (mcyH). Through the impairment of both the MC biosynthesis and MC transportation out of cells, K+ depletion caused an 85.89% reduction of extracellular MC content at the end of the study. However, with increasing in the available K+ concentrations, photosynthesis efficiency, the expression of ABC-transporter proteins, and the transcription of mcy genes displayed slight differences compared with those in the control group. This work represents evidence that K+ availability can regulate the physiological metabolic activity of M. aeruginosa and K+ deficiency leads to depressed growth and MC production in M. aeruginosa. (C) 2020 Elsevier Ltd. All rights reserved.