Cloning and expression of the insecticidal toxin gene tccB from Photorhabdus temperata M1021 in Escherichia coli expression system

Photorhabdus spp. has a high molecular weight Tc toxin with insecticidal activity. These toxins have been suggested as an alternative to BT toxin from Bacillus thuringiensis. Herein, we constructed a cosmid library with the genome of M1021 and screened the Escherichia coli clones showing insect toxicity by injecting each clone into Galleria mellonella larvae. In a total of 1020 clones, one clone with high insecticidal activity was selected and the nucleotide sequence of the cosmid of the clone was determined. In cosmid PtC28, a gene with 87% homology to the tccB gene of Photorhabdus temperata was found. Consequently, we have isolated the tccB gene cassette from the M1021 and expressed in E. coli expression vectors. The toxin was produced in the form of inclusion bodies but the denatured and refolded recombinant TccB showed strong mortality to the G. mellonella larvae.