[Displaying polyhistidine peptide on the cell surface of Bacillus thuringiensis by S-layer protein]

Cell surface layer (S-layer) is the outmost structure of bacterium cell and covers the intact cell. S-layer protein of Bacillus thuringiensis strain CTC (CTC protein) was used as carrier protein to display polyhistidine (polyHis) peptides on the cell surface. Series fusion protein genes were constructed by inserting DNA fragments encoding (6His)1, (6His)2, (6His)3, (6His)9 and (6His)15 polyHis peptides into CTC protein gene at the site of downstream of slh domain. With the help of recombinant plasmid pBMB-CSA, which contains operon csaAB needed for S-layer protein anchoring on cell surface, fusion protein genes were expressed in crystal negative B. thuringiensis strain 4Q7. SDS-PAGE profiles demonstrated that all the fusion proteins except CTC-(6His)15 were expressed. Ni-NTA-agarose beads binding test showed that all recombinant strains could attach to agarose beads except 4Q7 (pBMB-CSA, pBMB-SH15). Cd2+ adsorption test indicated that the adsorption ability of all recombinant strains except 4Q7 (pBMB-CSA, pBMB-SH15) were higher than that of host strains. The Cd2+ adsorption quantity of the recombinant strain with strongest adsorption ability was twice higher than that of host strain.