Enhancing the insecticidal activity of new Bacillus thuringiensis X023 by copper ions
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Microbial Cell Factories Open Access
RESEARCH
Enhancing the insecticidal activity of new Bacillus thuringiensis X023 by copper ions Zhuolin Liu†, Junyan Xie†, Ziru Deng, Mulan Wang, Dandan Dang, Sha Luo, Yunfeng Wang, Yunjun Sun, Liqiu Xia and Xuezhi Ding*
Abstract 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. Keywords: Bacillus thuringiensis, Copper ion, ICP, Proteome, Plutella xylostella Introduction Insecticidal crystal proteins (ICPs) produced by Bacillus thuringiensis (Bt) are well-known eco-friendly biological pesticides and insecticides with high specificity and efficiency. ICPs, except for the vegetative insecticidal protein (Vip), were formed during sporulation [1], and were also known as “parasporal crystalline” [2]. The cry gene of Bt is responsible for the insecticidal activity and has been successfully transferred to plants to provide resistance *Correspondence: [email protected] † Zhuolin Liu and Junyan Xie contributed equally to this work Hunan Provincial Key Laboratory of Microbial Molecular Biology, State Key Laboratory of Developmental Biology of Freshwater Fish, College of Life Science, Hunan Normal University, Changsha 410081, China
to pests [3–5]. However, insect resistance to Bt inevitably develops with the increase in the usage of bioinsecticides; thus, strategies to overcome this resistance are developing [6], such as isolating new serotypes strains and genetic engineering, are needed. Several factors, including mineral element, affect ICP productivity. Meta
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