Chemical structure and mechanism of polysaccharide on Pb2+ tolerance of Cordyceps militaris after Pb2+ domestication.

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In this study, the purified polysaccharide (DCP-I) was extracted from Cordyceps militaris domesticated with Pb 2+. After that, the structural feature and mechanism of lead resistance of DCP-I were investigated using novel approaches. The results showed that the average molecular weight of DCP-I was 1.206 × 10 3 kDa and mainly consist of Rhamnose, Galactose, Glucose, Galacturonic acid and Glucuronic acid in a molar ratio of 0.130:47.687:40.784:1.795:0.48. Besides, the main chain of DCP-I was composed by →6)-Galp-(1→, →4)-Glcp-(1→ and →1,4)-Glcp-(6→, while the side chain was →1)-Rhaf-(2→ and D-Glcp-(1→, and the DCP-I contained Alacturonic acid and Glucuronic acid. In addition, the result of Congo red test showed that DCP-I did not exist triple-helical structures. SEM, EDX and XPS analyses results showed that the functional groups of DCP-I related to C, H and O (-OH, -COOH and -C=O) could combined with Pb 2+ effectively. The adsorption processes were described by the Pseudo-second-order kinetic model (R 2 = 0.9978) and Langmuir isotherm (R 2 = 0.9979) for Pb 2+ indicating that adsorption process of DCP-I to Pb 2+ was a kind of single molecular layer chemical adsorption.