Abstract:SigE, encoded by sigE gene is an important sigma factor in the sporulation process. Many known genes and operons are controlled by this sporulation-specific factor, as well as most of cry genes in Bacillus thuringiensis. In this study, a sigE deletion mutant HD-73 (ΔsigE) was constructed by homologous recombination from Bacillus thuringiensis subsp. kurstaki HD-73 strain. The result showed that the mutant strain lost the ability of sporulation and crystallization of Cry protein. At the same time, the expression of insecticidal crystal proteins was severely reduced in HD-73 (ΔsigE) mutant, and growth speed of the mutant was affected intensively. The lacZ gene was fused with the promoter of the cry1Aa gene, and expressed in HD-73 (ΔsigE) mutant and HD-73 acrystalliferous mutant respectively. The activity of β-galactosidase expressed by lacZ gene in HD-73 (ΔsigE) mutant was much lower than that in the HD-73 acrystalliferous mutant. The ability of sporulation and crystallization of Cry protein was normally complemented by the expression of spoIIG operon, which contained the sigE gene after transformation with recombinant plasmid, and growth speed of the complemented strain also recovered. All the results indicated that for the B. thuringiensis subsp. Kurstaki strain, sigE gene is essential to sporulate and crystallize. Acquirement of HD-73 (ΔsigE) mutant will redound to understanding mechanism of Cry protein expression and regulation, crystallization and its relationship with sporulation.
