Genetically modified metallothionein/cellulose composite material as an efficient and environmentally friendly biosorbent for Cd2+ removal.

Metallothioneins (MTs) are a class of cysteine-rich metal-binding proteins. Cadmium (Cd) is one of the toxic heavy metal pollutants. In our previous research, the full-length cDNA of MT (Cd specificity) from freshwater crab (Sinopotamon henanense) (Sh MT) was cloned and genetically modified to Sh MT3 by site-directed mutagenesis to enhance the tolerance for Cd2+, however, it was limited in actual Cd2+ adsorption due to instability. Here, Sh MT3-CBM, a novel recombinant fusion protein, was prepared. CBM is a carbohydrate binding module that can specifically bind cellulose while Sh MT3 can effectively chelate Cd2+. The biosorbent Cellulose1- Sh MT3-CBM was obtained by screening suitable cellulose materials. The selective adsorption experiments showed that Cellulose1- Sh MT3-CBM had a preference for Cd2+. In low-concentration Cd2+ solutions, the removal efficiency was >99 %, and the adsorption equilibrium was reached within 15 min. The saturated adsorption capacity of Cellulose1- Sh MT3-CBM for Cd2+ is 180.35 ± 4.67 mg/g (Dry Weight). Regeneration experiments showed that adsorption efficiency was maintained after six cycles. The MTT experiment showed that Cellulose1- Sh MT3-CBM had low cytotoxicity. Meanwhile, Cellulose1- Sh MT3-CBM can preferentially remove Cd2+ in actual water samples and boiler sewage. In this study, an environmentally friendly biosorbent which can adsorb Cd2+ efficiently and quickly was prepared for actual water treatment. [Display omitted] • Sh MT3-CBM was obtained by genetic engineering technology. • Cellulose1- Sh MT3-CBM was obtained by immobilization technology. • In low concentration solution, the removal efficiency reaches >99 %. • Cellulose1- Sh MT3-CBM showed excellent reusability. • Cellulose1- Sh MT3-CBM is non-toxic to cells. [ABSTRACT FROM AUTHOR]