Expression and purification of recombinant TcdA. pHis-TcdA plasmid was transformed into B. megaterium protoplasts. Over 20 transformed colonies were picked up and the expression of rTcdA was induced by xylose. (A) Coomassie staining of SDS-PAGE from crude bacterial extracts: Lane 1 shows no xylose induction; Lane 2 to 4 shows three different clones with xylose induction; Lane 5 shows purified rTcdA after Ni-affinity and thyroglobulin chromatograph. M shows molecular weight marker and the top band indicates 250 kDa. (B) Western blot results of the purified native TcdA (lane 1) and rTcdA (lane 2).