Abstract
BackgroundBacillus thuringiensis X022, a novel strain isolated from soil in China, produces diamond-shaped parasporal crystals. Specific mineral nutrients, such as Mg, Cu, and Mn, influence insecticidal crystal proteins (ICP) expression and the effects of these elements vary significantly. However, the molecular mechanisms of the effects caused by mineral elements have yet to be reported.ResultsThe ICP are mainly composed of Cry1Ca, Cry1Ac, and Cry1Da, which have molecular weights of about 130 kDa. ICP production was most efficient when Cu2+ was added at concentrations ranging from 10−6 to 10−4 mol/L at an initial pH of 8.0. Addition of Cu2+ also evidently increased the toxicity of fermentation broth to Spodoptera exigua and Helicoverpa armigera. After analyzing changes in proteome and fermentation parameters caused by Cu2+ addition, we propose that Cu2+ increases PhaR expression and consequently changes the carbon flow. More carbon sources was used to produce intracellular poly-β-hydroxybutyrate (PHB). Increases in PHB as a storage material bring about increases of ICP production.ConclusionsBacillus thuringiensis X022 mainly expresses Cry1Ca, Cry1Ac, and Cry1Da. Cu2+ increases the expression of Cry1Da, Cry1Ca, and also enhances the toxicity of fermentation broth to S. exigua and H. armigera.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-015-0339-9) contains supplementary material, which is available to authorized users.
Highlights
Bacillus thuringiensis X022, a novel strain isolated from soil in China, produces diamond-shaped parasporal crystals
The present study showed that appropriate concentrations of Cu2+ have positive effects on the expression of Cry1Da and Cry1Ca in B. thuringiensis
The results show that the medium with 10−6 mol/L Cu2+ has been found to increase the efficacy and potency of B. thuringiensis toxins in insect control
Summary
Bacillus thuringiensis X022, a novel strain isolated from soil in China, produces diamond-shaped parasporal crystals. Specific mineral nutrients, such as Mg, Cu, and Mn, influence insecticidal crystal proteins (ICP) expression and the effects of these elements vary significantly. The toxicity of insecticidal crystal proteins (ICP) produced by Bacillus thuringiensis to agricultural pests and disease vectors is well known. Because of the development of insect resistance to B. thuringiensis [4, 5], screening for new serotypes that bear novel crystal genes is an important endeavor. Results showed that Mn is the most critical element for the biosynthesis of both toxins at 10−6 mol/L concentration. Kurt et al [8] found that omission of FeSO4 from the medium results in reductions in Cry3Aa yield in B. thuringiensis Mm2 by about 50 %
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