Transition Phase Regulator AbrB Positively Regulates the Gene Expression in Bacillus thuringiensis.

Bacillus thuringiensis secreted insecticidal proteins (Sip) are a secretion that is toxic to coleopteran pests. However, the transcriptional mechanism of genes is still unknown. The transcriptional regulation of the gene and the expression of the Sip1Ab1 protein were investigated in this study. The results demonstrated that the secretion of the Sip1Ab1 protein in HD73 was almost the same as that in the original QZL38 strain during the transition phase. Analysis of the β-galactosidase activities of in both the HD73 and mutant strains indicated that the transcription of is dependent on AbrB. Electrophoretic mobility shift assays showed that AbrB could bind with the promoter, and two binding sites of AbrB in the region of the promoter of were determined by DNase I footprinting assays. All of the above-described results proved that AbrB positively regulates the gene. Bacillus thuringiensis Sip proteins are secreted insecticidal toxins that are toxic to coleopteran pests. In this study, we investigated the transcriptional mechanism of the gene and showed strong evidence that Sip1Ab1 is secreted in the transition phase and that AbrB, a transition phase regulator that is usually a repressor, positively and directly regulates . Reports of AbrB positive regulation are rare, even in Bacillus subtilis. To the best of our knowledge, no toxic gene has been reported to be positively regulated by AbrB in Bacillus species.