Metal Effects on Carotenoid Content of Cyanobacteria

Cyanobacteria exhibit an extraordinary resistance to many environmental factors including metal pollution. The present study was conducted to explore the possibility of using cyanobacteria for bioremediation of Co2+ and Zn2+ as essential nutrient elements for the growth of cyanobacteria which detoxify these metals. Anabaena oryzae and Tolypothrix tenuis cells collected from paddy fields expressed different degrees of tolerance to metal(s) stress due to cobalt, zinc, copper and mercury. The tolerance of these species under different concentrations (1, 10 and 100 ppm) of heavy metals was determined. Observations were made on every 2nd day for the period of 12 days. Among the organisms studied, T. tenuis was more sensitive to the metals than A. oryzae. Copper at 1 ppm on the 8th day gave maximum carotenoid content (6.652 μg mL-1) in A. oryzae. The mercury treated cells showed lethality at (1, 10 and 100 ppm). There was gradual increase of carotenoid content after 12 days, especially at (1 and 10 ppm) of Co2+ and Zn2+ in A. oryzae. This indicated the possibility of application of this species for detoxification of effluents.