Sip1Ab gene from a native Bacillus thuringiensis strain QZL38 and its insecticidal activity against Colaphellus bowringi Baly

In this study, we collected 540 soil samples from northeast China and isolated the wild-type strain of Bacillus thuringiensis (Bt) by identifying and cloning 9 Bt strains that expressed the secreted insecticidal protein (Sip) gene. We selected the strain QZL38 for further study. The sip gene was identified from the Bt strain QZL38 using polymerase chain reaction (PCR). We sequenced a 1095-base pair fragment of DNA that encodes 364 amino acid residues of a 41.18kDa pro-toxin and compared it with the registered Sip1Ab protein amino acid residue sequence. The sequence was submitted to GenBank with the accession no. KP231523, and the gene was named sip1Ab. The Sip1Ab protein expressed in Escherichia coli showed insecticidal activity against Colaphellus bowringi Baly, with an LC50 of 1.051gmL(-1). To identify the active fragment of the Sip1Ab toxin, four pairs of primers with different truncation positions were designed, and the recombinant proteins were expressed in E.coli. The truncated Sip protein expressed in E.coli showed insecticidal activity against C. bowringi Baly. The insecticidal activity of the recombinant proteins against C. bowringi Baly from the Sip1Ab signal peptide after removal of 30 amino acid residues showed an LC50 of 1.078gmL(-)1. Sip proteins may play an important role in the prevention and control of the C. bowringi Baly.