Activity of the Bacillus thuringiensisNprRNprX cellcell communication system is co-ordinated to the physiological stage through a complex transcriptional regulation

NprR is a quorum sensor of the RNPP family found in bacteria of the Bacillus cereus group. In association with its cognate peptide NprX, NprR controls the expression of genes essential for survival and sporulation of Bacillus thuringiensis during its necrotrophic development in insects. Here, we report that the nprRnprX genes are not autoregulated and are co-transcribed from a sigma A-dependent promoter (PA) located upstream from nprR. The transcription from PA starts at the onset of the stationary phase and is controlled by two transcriptional regulators: CodY and PlcR. The nutritional repressor CodY represses nprRnprX transcription during the exponential growth phase and the quorum sensor PlcR activates nprRnprX transcription at the onset of stationary phase. We show that nprX is also transcribed independently of nprR from two promoters, PH and PE, dependent on the sporulation-specific sigma factors, sigma H and sigma E respectively. Both promoters ensure nprX transcription during late stationary phase while transcription from PA has decreased. These results show that the activity of the NprRNprX quorum sensing system is tightly co-ordinated to the physiological stage throughout the developmental process of the Bacillus.