Removal of cadmium and manganese by a non-toxic strain of the freshwater cyanobacterium Gloeothece magna

The ability of both living and dry cells of Gloeothece magna, a non-toxic freshwater cyanobacterium, to adsorb cadmium and manganese is demonstrated in this study. Chlorophyll a content of living cells was not influenced by either cadmium or manganese concentrations, indicating that adsorption of both Cd2+ and Mn2+ by living cells of G. magna, was independent of the metabolic state of the organism. Moreover, the adsorption of both Cd2+ and Mn2+ to living cells and dry cells, was dependent on the metal concentrations, and fitted the Freundlich adsorption isotherm. However, dry cells had larger binding capacity for both Cd2+ (Kf=912.6) and Mn2+ (Kf=2398) than living cells (Kf=151.4 & 63, respectively). The role of the capsular polysaccharides, the main constituents of the cyanobacterial envelope, in binding these two metals was also studied. Polysaccharide extracts of this organism adsorbed high amounts of both Cd2+ (115–425 μg mg−1) and Mn2+ (473–906 μg mg−1). This study suggests that G. magna would probably be cultured in water bodies contaminated by heavy metals to ameliorate their toxicity. Also dry material of this cyanobacterium being a non-toxic species, could be used as a safe biofilter to remove toxic metals from drinking water.