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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 (V max) and the half saturation constant for uptake (K m) remained constant. Inhibition of V max by accumulated phosphate was observed and the inhibition constant was determined. Due to the high V max 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.