Transcription of dxr1 is controlled by SigH in Bacillus thuringiensis

Abstract:

[Objective] Terpenoids are widely present in various organisms and play key roles in all forms of life. Two pathways have been found for the biosynthesis of terpenoids:the mevalonate (MVA) pathway and 2-methyl-D-erythritol-4-phosphate (MEP) pathway. 1-deoxy-D-xylulose-5-phosphate reductoisomerase (DXR) is a key enzyme in the MEP pathway that catalyzes 1-deoxy-D-xylulose-5-phosphate to generate MEP. DXR is encoded by a dxr gene in Bacillus subtilis, while two dxr genes (dxr1 and dxr2) encode DXR in Bacillus thuringiensis (Bt). To determine the mechanism of transcriptional regulation and the function of dxr gene, we analyzed the transcriptional regulation of dxr1 gene and phenotype of dxr1 and dxr2 mutants of Bt HD73. [Methods] Transcriptional start site was analyzed by 5'RACE. Transcriptional activity of dxr1 promoter (Pdxr1) was analyzed by promoter fusions with lacZ gene. dxr1 and dxr2 mutants of Bt HD73 strain were constructed by homologous recombination. Comparison of the Cry1Ac protein production was determined by protein quantitation. DXR activity was determined by DXR detection kit. [Results] A G residue located 39 bp upstream from the dxr1 start codon was identified. The transcriptional activity of Pdxr1 was sharply decreased in sigH mutant compared with that in HD73 wild-type. Mutation of dxr1 or dxr2 has no significant differences on growth, sporulation efficiency and Cry1Ac protein production. However, the DXR activity was decreased in the mutants. [Conclusion] Transcription of dxr1 is controlled by SigH. Deletion of dxr genes influenced the activity of DXR.

Key words:Bacillus thuringiensis;MEP pathway;DXR;dxr gene;transcriptional regulation