Phosphorus uptake and photosynthesis by phosphate-limited cultures of the cyanobacterium Microcystis aeruginosa

Microcystis aeruginosa AK1 was grown in phosphorus-limited continuous cultures with an 8:16 light-dark cycle. The photosynthesis and phosphorus uptake kinetics were studied and compared with those of other cyanobacteria.Compared to that of light-limited cultures the light-harvesting capacity of P-limited cultures was low. The maximal photosynthetic rate per unit chlorophyll remained constant whereas the light-harvesting efficiency increased with a decrease in the severity of the limitation. The maximal phosphate uptake rate (Vmax) and the half saturation constant for uptake (Km) remained constant. Inhibition of Vmax by accumulated phosphate was observed and the inhibition constant was determined.Due to the high Vmax and the low P-content, Microcystis outcompeted Oscillatoria in conditions where the supply of phosphorus limited the growth rate. The results are interpreted in an ecological context.