Potassium-induced inhibition of photosynthesis and associated electron transport chain of Microcystis: Implication for controlling cyanobacterial blooms

Potassium toxicity to survival and growth of Microcystis has been investigated for the first time by taking photosynthetic parameters and change in internal pH of Microcystis. The concentration of potassium reducing 50% population of Microcystis was found to be 6 mM. At this concentration, the internal pH of cells increased from 7.2 to 9.8 in comparison to control. 6.0 mM concentration of potassium reduced protein content by 44% and generated Na+ efflux of 55% as compared to control. O2 evolution, ATP content and CO2 fixation were found to be very sensitive to above K+ concentration and registered a respective decline of 38, 32 and 36%. PS II was the primary site of action depicting about 35% inhibition at above K+ concentration. PS I and whole electron transport chain were also inhibited but the extent was less pronounced in comparison to PS II. A definite correlation between requirement of Na+ for growth and maintenance of cytoplasmic pH was observed. K+-induced loss of Na+ from cells of Microcystis could result in increase in internal pH, which in turn affects survival, growth, and other physiological parameters of Microcystis. Thus, K+ appears to hold excellent potential for the control of Microcystis blooms in fresh water ponds and lakes.