The effect of heavy metals was seen on the oxygen evolution pattern of a unicellular, non‐heterocystous cyanobacterial strain of Synechococcus spp. PCC 7942. It was grown in a BG‐11 medium supplemented with heavy metals, namely, nickel, copper, cadmium and mercury. Final concentrations of the heavy metal solution used in the culture were 0.1, 0.4 and 1 μM. All the experiments were performed in the exponential phase of the culture. Oxygen‐evolving photosystem II (PS II) particles were purified from Synechococcus spp. PCC 7942 by a single‐step ‐affinity column chromatography after solubilization of thylakoid membranes with sucrose monolaurate.
Oxygen evolution was measured with Clark type oxygen electrode fitted with a circulating water jacket. The light on the surface of the vessel was The cultures were incubated in light for 15 minutes prior to the measurement of oxygen evolution. Oxygen evolution was measured in assay mixture containing phosphate buffer (pH−7.5, 0.1 M) in the presence of potassium ferricyanide as the electron acceptor. The preparation from the control showed a high oxygen‐evolving activity of 2, 300–2, 500 pmol while the activity was decreased in the cultures grown with heavy metals. The inhibition of oxygen evolution shown by the organism in the presence of different metals was in the order Hg>Ni>Cd>Cu. Such heavy metal resistant strains will find application in the construction of PS II‐ based biosensors for the monitoring of pollutants.
