Secretory expression of recombinant diphtheria toxin mutants in B. Subtilis

Three diphtheria toxin (DT) mutants CRM-197, DT-del (148) and DT-E148S-K516A-F530A were cloned in B. Subtilis plasmid PSM604 under the subtilisin signal sequence. The expression was effective in both SMS300 and SMS118, but higher yield of 7.1 mg/L was observed in SMS300 compared with 2.1 mg/L in SMS118. Western blot showed that the recombinant protein could be effectively secreted into the culture medium as a 58 ku peptide, and could be degraded into two peptides of 37 ku and 21 ku.