Cadmium(II) sequestration characteristics by two isolates of Synechocystis sp. in terms of exopolysaccharide (EPS) production and monomer composition

We investigated cadmium(II) resistance and its association with exopolysaccharide (EPS) production in cyanobacteria. Increased EPS production was associated with Cd(II) resistance. The most resistant isolate, Synechocystis sp. BASO670, secreted the greatest amount of EPS (548 mg/L). EPS production by Synechocystis sp. BASO670 and Synechocystis sp. BASO672 was increased following exposure to 15 and 35 ppm Cd(II). Monomer composition of EPS belonging to each isolate was changed after Cd(II) treatment. Uronic acid contents of Cd(II) treated cells were higher than control cells of each isolate. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analysis confirmed that a considerable amount of metals had precipitated on the cell surface. Fourier transform infrared (FT-IR) spectrum analysis of EPSs belonging to both isolates indicated the presence of C–H and C–O group, which may serve as binding sites for divalent cations.