Proteomic Identification of a Novel Toxin Protein (Txp40) from Xenorhabdus nematophila and Its Insecticidal Activity against Larvae of Plutella xylostella

For the identification of a novel insecticidal protein, a two-dimensional liquid chromatography (PF-2D) system was used in a quantitative proteomic analysis of Xenorhabdus nematophila CBNU strain isolated from entomophagous nematode Steinernema carpocapsae. Protein patterns obtained from minimum and maximum insecticidal activities during cultivation were contrasted, and a novel toxin protein (Txp40) was identified by MALDI-TOF/MS. The DNA sequence of the cloned toxin gene (1089 bp) has an open reading frame encoding 363 amino acids with a predicted molecular mass of 41162 Da. The txp40 identified in this study is most closely related to the known txp40 cloned from X. nematophila EB (ADQ92844) with 94.4% identical sequence residues. Following the expression of the newly identified toxin gene in Escherichia coli, the insecticidal activity of the recombinant toxin protein was determined against Plutella xylostella larvae; a 56.7% mortality rate was observed within 24 h.