Influence of calcium on cadmium uptake and toxicity to the cyanobacterium Nostoc muscorum Meg 1

It is well known that Ca²⁺ interferes with uptake and expression of toxicity of Cd²⁺ in numerous organisms. This study demonstrated that the morphological alterations expressed in the cyanobacterium Nostoc muscorum Meg 1 cells exposed to 0.5 mg L⁻¹ Cd²⁺ for 7 days were prevented when 10 mg L⁻¹ Ca²⁺ was included in the experimental set-up. The spectroscopic analysis confirmed a severe reduction in contents of chlorophyll a, phycocyanin, allophycocyanin, phycoerythrin, carotenoids and total protein at the end of 168 h (7 days) in presence of Cd²⁺; inclusion of Ca²⁺ significantly lessened these effects. Heterocyst frequency, nitrogenase and, glutamine synthetase activities were similarly improved in the presence of Ca²⁺. Uptake studies showed a reduction in 94% biosorption of supplied Cd²⁺ to 50% in the presence of Ca²⁺ indicating its competition with Cd²⁺ binding onto the cyanobacterial cell surfaces.