Removal of Ni2+ and Cd2+ by Surface Display of Polyhistidine on Bacillus subtilis Spore Using CotE Anchor Protein

In this paper, we report removing heavy metal using Bacillus subtilis spore surface display system. We used CotE protein as an anchoring motif because of its high abundance and location in the outer coat layer. And we inserted His12 (double histidine 6 tag) at the C-terminal end of anchoring motif. The proper expression of CotE-His12 fusion protein (22.8 kDa) was confirmed by western blot. We confirmed the surface expression of the CotE-His12 fusion protein using flow cytometry. We tried Ni2+ and Cd2+ adsorption with recombinant spore DB104 (pCotE-His12) and DB104 spore. The amount of adsorbed Ni2+ was 18.2 nmol/mg for DB104 spore and 82.4 nmol/mg for DB104 (pCotE-His12) spore. In the case of Cd2+, the adsorbed amount was 32.6 nmol/mg for DB104 spore and 79.1 nmol/mg for DB104 (pCotE-His12) spore. This means that our spore displayed His12 system can be generally applied for the removal of various kind of heavy metals in the field.