Activity of the B acillus thuringiensis NprR – NprX cell–cell communication system is co‐ordinated to the physiological stage through a complex transcriptional regulation

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