A cell–cell communication system regulates protease production during sporulation in bacteria of the Bacillus cereus group

Abstract

SummaryIn sporulating Bacillus, major processes like virulence gene expression and sporulation are regulated by communication systems involving signalling peptides and regulators of the RNPP family. We investigated the role of one such regulator, NprR, in bacteria of the Bacillus cereus group. We show that NprR is a transcriptional regulator whose activity depends on the NprX signalling peptide. In association with NprX, NprR activates the transcription of an extracellular protease gene (nprA) during the first stage of the sporulation process. The transcription start site of the nprA gene has been identified and the minimal region necessary for full activation has been characterized by promoter mutagenesis. We demonstrate that the NprX peptide is secreted, processed and then reimported within the bacterial cell. Once inside the cell, the mature form of NprX, presumably the SKPDIVG heptapeptide, directly binds to NprR allowing nprA transcription. Alignment of available NprR sequences from different species of the B. cereus group defines seven NprR clusters associated with seven NprX heptapeptide classes. This cell-cell communication system was found to be strain-specific with a possible cross-talk between some pherotypes. The phylogenic relationship between NprR and NprX suggests a coevolution of the regulatory protein and its signalling peptide.

Structural basis for the activation mechanism of the PlcR virulence regulator by the quorum-sensing signal peptide PapR

“…observed, pointing out their important role in adaptative and virulence processes (27)(28)(29)(30)(31)(32). This clearly identifies these regulators as major targets for the search of new molecules with applications in medical, food, and biotechnology areas.…”

Division of labour and terminal differentiation in a novel Bacillus thuringiensis strain

“…The sequences of the sensor regulators (PlcR and NprR) and of their cognate peptides (PapR and NprX) from LM1212 were 100% identical to those of B. cereus G9241 (data not shown), a strain encoding the entire anthrax toxin biosynthetic complex and that was responsible for a human anthrax case (Hoffmaster et al, 2004). This is surprising because PlcR-PapR and NprR-NprX are phylogenetically unrelated and these two systems are supposed to have evolved independently (Perchat et al, 2011). Thus, like its close relative B. cereus G9241, LM1212 may be a potential mammalian pathogen.…”

“…Both these strains cluster within the B. cereus group clade that contains B. anthracis, a clade variously described as 'group 1', 'group III', 'the anthrax clade' or the 'C clade' (Priest et al, 2004;Sorokin et al, 2006;Guinebretière et al, 2010;Raymond et al, 2010b). The PlcR-PapR and NprR-NprX systems (Perchat et al, 2011) of LM1212 were found identical to those of the anthrax-casing B. cereus G9241, although it contained no anthrax toxin genes and did not produce a capsule. Broadly, strains in the anthrax clade are more likely to be associated with vertebrate hosts, whereas most entomopathogenic Bt strains fall into a different clade (Raymond and Bonsall, 2013b).…”

“…These genomic analyses confirm that LM1212 is a Bt strain. Moreover, the LM1212 genome contains genes for PlcR and NprR, which are quorum-sensing regulators specific to the B. cereus group bacteria (Slamti and Lereclus, 2005;Perchat et al, 2011). The sequences of the sensor regulators (PlcR and NprR) and of their cognate peptides (PapR and NprX) from LM1212 were 100% identical to those of B. cereus G9241 (data not shown), a strain encoding the entire anthrax toxin biosynthetic complex and that was responsible for a human anthrax case (Hoffmaster et al, 2004).…”

“…The activity was measured as previously described and expressed as units per milligram of protein (Perchat et al, 2011). Each assay was repeated three times.…”