When the calY gene deleted the intact signal peptide expressed in E. coli BL21 (DE3), a large amount of (His)6-camelysin (molecular mass approximately 25 kDa) was produced in the form of solution (Fig. 2a). The (His)6-camelysin was purified by affinity chromatography

on a HisTrap FF crude 1-mL Galunisertib column (Fig. 2b). A B. thuringiensis integration plasmid pKESX was constructed to integrate erm into the B. thuringiensis chromosome. Plasmid pKESX was transformed by electroporation into B. thuringiensis KCTF12. The transformants conferring both chloramphenicol sensitivity and erythromycin resistance were selected as calY replacement mutants. Proper gene replacements of several isolates were confirmed by PCR amplification with appropriate primers (Fig. 3a). When the temperature-sensitive plasmid was apparently recombined with the calY gene in the chromosome by a single cross-over, a recombinant strain was generated containing the whole sequence of pKESX in the chromosomal DNA, which conferred both Gefitinib cell line chloramphenicol and erythromycin resistance. PCR analysis indicated that the plasmid pKESX was recombined with KCTF12 chromosome by a double cross-over, generating a 2.8-kb fragment containing the homologous arms and erm by the primer pair P7/P9 (Table 2). In contrast, the fragment was 2.1 kb with a template of KCTF12. At the same time, the primer pair P1/P2

(Table 2) was used to confirm that when the calY was replaced successfully by erm, only the 3-ends of the calY of about 56 bp were left, which could conveniently be used in the complementation mutants. The complementation

plasmid pKPC was electroporated into strain KCTF, and the transformants conferring chloramphenicol resistance were designated KCTFC. Transformants were confirmed by PCR amplification with chromosomal DNA as templates (Fig. 3b). The PCR analysis indicated that the plasmid pKPC was successfully electroporated into strain KCTF, thereby generating a 913-bp fragment containing the calY and its promoter in the plasmid, and a 1510-bp fragment containing the promoter of the calY and erm in the chromosome with the primer pair P11/P12 (Table 2). In contrast, the fragment was 913 bp in KCTF12, and 1510 bp in KCTFC with the primer pair P11/P12. Western blot analysis (Fig. 3c) confirmed that the level of expression ALOX15 of camelysin was either deficient or successfully complemented. It also confirmed that the camelysin, which was replaced in the study, was a single copy in the chromosome of the B. thuringiensis. The global proteins of stationary phase KCTF12, KCTF and KCTFC cultures were analyzed and compared by SDS-PAGE (Fig. 4a). Strain KCTF12 produced a large protein band of metalloproteinase camelysin protein, suggesting that the expression of camelysin was very high in B. thuringiensis. As also shown in the SDS-PAGE, one protein band disappeared in KCTF. When the camelysin was complemented in KCTFC, the protein band reappeared.