Photodynamic action of hypericin on cyanobacteria, Synechocystis and Synechoccus (Anacystis nidulans)

Abstract

The photodynamic action of hypericin on photosynthesis and respiration were monitored in Synechocystis sp PCC 6803 and Synechoccus ATCC 6311 (Anacystis nidulans). An oxygen electrode was used to measure net oxygen evolution or consumption. The amount of hypericin required to inhibit photosynthesis was quantitively determined. Photosynthesis was completely inhibited in Synechocystis when the molar ratio of chlorophyll/hypericin was about 70:1. Higher concentrations of hypericin did not stop the uptake of oxygen, but rather stimulated the process in the light. Hypericin was readily washed out of the cells forming no permanent associations in the bacterial cell. Hypericin inhibited electron transfer and consequently oxygen production by PSII particles. For half maximum inhibition of oxygen evolution, with PSII membrane particles, the molar ratio of chlorophyll/hypericin was about 10:1.