Lead (Pb²⁺) adsorption characteristics and sugar composition of capsular polysaccharides of cyanobacterium Calothrix marchica

The ability of living cells of the cyanobacterium Calothrix marchica to adsorb Pb²⁺ was studied. C. marchica showed high efficiency to remove Pb²⁺. The desorbing agent, EDTA could effectively desorb Pb ²⁺ from cyanobacterial cells, suggesting that Pb²⁺ was mainly adsorbed on the cell surface, presumably binding with certain functional groups of capsular polysaccharides (CPS). Subsequently, production of CPS, their sugar contents and ability to absorb Pb²⁺ were studied in details. CPS production by C. marchica increased as growth proceeded. C. marchica showed the highest CPS content of 26.85 mg g^-1 dry weight after 30-day of cultivation. The major components of CPS were carbohydrates and protein (37.6% and 34.7% of total CPS, respectively). The neutral sugars presented in CPS of C. marchica were xylose, arabinose, ribose, rhamnose, galactose, glucose, mannose and fructose. Acidic sugars including galacturonic and glucuronic acids were also found. The highest acidic sugar content was found after 30 days of cultivation. The extracted CPS of C. marchica could adsorb 64.15±5.09 mg Pb per g CPS. C. marchica cells with intact CPS adsorbed 3.42±0.07 mg Pb g^-1 dry weight, which was not significantly different from cells without CPS. From these results, it can be concluded that C. marchica was able to remove Pb²⁺ rapidly and efficiently, and to produce high amount of CPS with acidic sugars 117.73±2.15 μg g^-1 as the major component, suggesting that C. marchica could serve as one of the alternative bioadsorbers for Pb²⁺ in bioremoval systems.