and shipped to Invitrogen (Shanghai, China) for nucleotide sequencing. Based on known partial sequences, primers Sf1–Sf2 and Sr1–Sr2 (Table 1) were designed to amplify the full-length gene by SON-PCR (Fig. 2a). SON-PCR reaction conditions were performed as previously described (Antal et al., 2004). The Trichostatin A cost SON-PCR derived products were recovered, cloned, and sequenced. The full-length nucleotide sequence of novel vip1 gene was edited using SeqMan5.0 (DNAStar). To confirm that the B. cereus strain HL12 that contained novel vip1-type gene and also has vip2-type gene, primer pair, vip2a and vip2s (Table 1), was designed by aligning nucleotide sequences of vip2Aa3, vip2Ac1, vip2Af1, and vip2Ba2 (GenBank accession numbers: HM43909, AAO86513, ACH42759, and CAI43279). The vip2-type gene was amplified, cloned, and sequenced. The primer pair, Vip1s-NdeI and Vip1a-XhoI, was used to amplify the vip1Ac1 gene while the vip2Ae3 gene was amplified using Vip2s–EcoRI/Vip2a–BamHI primer set (Table 1). The single-expression vectors (pCO-vip1Ac1 and pCO-vip2Ae3) and co-expression vector (pCO-vip2Ae3–vip1Ac1) were constructed by digestion with Proteasome function endonucleases NdeI, XhoI, EcoRI, and BamHI. Their constructed map was shown in Fig. 3. The construction of co-expression vector was by digesting pCO-vip1Ac1
with EcoRI and BamHI and subsequently ligating the predigested vip2Ae3 gene with the same endonucleases. All the constructed plasmids were sequenced to verify the gene inserts. The constructed plasmids were transformed into E. coli strain BL21. A single colony of positive E. coli strain BL21, cultured on solid LB medium with kanamycin (50 μg mL−1) and chloramphenicol (34 μg mL−1), was picked and grown in LB broth at 37 °C on a shaker (250 r.p.m.). At an optical density (600 nm) of 0.5, isopropyl-β-d-thiogalactopyranoside (IPTG) was added to a final concentration of 1 mM to induce expression. After induction for 4 h at 37 °C, the expression proteins were subjected to SDS–PAGE analysis and bioassay for insecticidal activity. The expression
proteins were purified as previously CYTH4 described (Shi et al., 2004). An E. coli strain BL21 suspension containing Vip1Ac1 and Vip2Ae3 was assayed against Tenebrio molitor (Coleoptera), Holotrichia oblita (Coleoptera), Spodoptera exigua (Lepidoptera), Helicoverpa armigera (Lepidoptera), Chilo suppressalis (Lepidoptera), Culex quinquefasciatus (Diptera), Aphis gossypii (Homoptera). The E. coli strain BL21 having only vector pCOLADuet-1 was a negative control. The bioassay was performed according to standardized methods (Pang et al., 1992; Li et al., 2005; Fang et al., 2007; Sattar et al., 2008). The PCR amplification of genomic DNA using Vip1s and Vip1a primers showed that 16 of 25 B. cereus isolates and the reference strain (CGMCC ID: 0984) had vip1-type genes. Using primers Vip1f and Vip1r, a 1140-bp fragment was also obtained from 17 B. cereus strains.