Enhancing the insecticidal activity of new Bacillus thuringiensis X023 by copper ions

Background A new Bacillus thuringiensis X023 (BtX023) with high insecticidal activity was isolated in Hunan Province, China. The addition of metals (Cu, Fe, Mg and Mn) to the medium could influence the formation of spores and/or insecticidal crystal proteins (ICPs). In previous studies, Cu ions considerably increased the synthesis of ICPs by enhancing the synthesis of poly-β-hydroxy butyrate. However, the present study could provide new insights into the function of Cu ions in ICPs. Results Bioassay results showed that wild strain BtX023 exhibited high insecticidal activity against Plutella xylostella. The addition of 1 × 10−5 M Cu2+ could considerably increase the expression of cry1Ac and vip3Aa, and the insecticidal activity was enhanced. Quantitative real-time polymerase chain reaction (qRT-PCR) and proteomic analyses revealed that the upregulated proteins included amino acid synthesis, the glyoxylate pathway, oxidative phosphorylation, and poly-β-hydroxy butyrate synthesis. The Cu ions enhanced energy metabolism and primary amino acid synthesis, will providing abundant raw material accumulation for ICP synthesis. Conclusion The new strain BtX023 exerted a strong insecticidal effect on P. xylostella by producing ICPs. The addition of 1 × 10−5 M Cu2+ in the medium could considerably enhance the expression of the cry1Ac and vip3Aa genes, thereby further increasing the toxicity of BtX023 to Helicoverpa armigera and P. xylostella by enhancing energy synthesis, the glyoxylate cycle, and branched-chain amino acids synthesis, but not poly-β-hydroxy butyrate synthesis.