[Expression of alpha-toxin gene of Clostridium perfringens type A and its primary immunological protective function]

Alpha-toxin gene was amplified from chromosomal DNA of Clostridium perfringens type A by polymerase chain reaction (PCR). PCR product was inserted into vector pGEM-T directly. The cloned recombinant plasmid pXCPA02 possesses positive nucleotide sequence of alpha-toxin. A 1.2 kb alpha-toxin gene fragment was cleaved with restriction endonucleases Nco I /EcoR I from plasmid pXCPA02, and then inserted into an expression vector pET-28c which cleaved with Nco I /EcoR I by blunt-end ligation. The recombinant expression plasmid pXETA02 was studied in detail by restriction endonucleases analysis and nucleotide sequencing. The results showed that the recombinant expression pXETA02 possessed a positive alpha-toxin gene sequence and reading frame. BL21 (DE3) (pXETA02) could produce alpha-toxin and the expressed products were recognized by alpha-toxin monoclonal antibodies with ELISA and Western blot. The expression optimization result indicated that the alpha toxin gene expression optimized condition with IPTG induction is culture medium pH 7.5, culture temperature 37 degrees C, joining IPTG to final concentration 0.8 mmol/L when the recombinant strain growth density OD600 achieved 0.8, and induction time 5h. The expression level of the alpha-toxin proteins were about 34.28% of total cellular protein with IPTG induction by SDS-PAGE and thin-layer gel scanning analysis. The alpha toxin gene expression optimized condition with lactose induction is culture medium pH 7.5, culture temperature 37 degrees C, joining lactose to final concentration 0.1 g/L when the recombinant strain growth density OD600 achieved 0.8, and induction time 5h. The expression level of the alpha-toxin proteins were about 23.82% of total cellular protein with lactose induction by SDS-PAGE and thin-layer gel scanning analysis. More importantly, Immunization in a mouse model with crude preparation containing the alpha-toxin protein inclusion bodies or inactivated recombinant strain induced protection against at least 1 MLD of the toxin from Clostridium perfringens type A.