A cell-cell signaling peptide activates the PlcR virulence regulon in bacteria of the Bacillus cereus group

PlcR is a pleiotropic regulator that activates the expression of genes encoding various virulence factors, such as phospholipases C, proteases and hemolysins, in Bacillus thuringiensis and Bacillus cereus. Here we show that the activation mechanism is under the control of a small peptide: PapR. The papR gene belongs to the PlcR regulon and is located 70 bp downstream from plcR. It encodes a 48-amino-acid peptide. Disruption of the papR gene abolished expression of the PlcR regulon, resulting in a large decrease in hemolysis and virulence in insect larvae. We demonstrated that the PapR polypeptide was secreted, then reimported via the oligopeptide permease Opp. Once inside the cell, a processed form of PapR, presumably a pentapeptide, activated the PlcR regulon by allowing PlcR to bind to its DNA target. This activating mechanism was found to be strain specific, with this specificity determined by the first residue of the penta peptide.     

Differential proteomic analysis of the Bacillus anthracis secretome: distinct plasmid and chromosome CO2-dependent cross talk mechanisms modulate extracellular proteolytic activities

The secretomes of a virulent Bacillus anthracis strain and of avirulent strains (cured of the virulence plasmids pXO1 and pXO2), cultured in rich and minimal media, were studied by a comparative proteomic approach. More than 400 protein spots, representing the products of 64 genes, were identified, and a unique pattern of protein relative abundance with respect to the presence of the virulence plasmids was revealed. In minimal medium under high CO(2) tension, conditions considered to simulate those encountered in the host, the presence of the plasmids leads to enhanced expression of 12 chromosome-carried genes (10 of which could not be detected in the absence of the plasmids) in addition to expression of 5 pXO1-encoded proteins. Furthermore, under these conditions, the presence of the pXO1 and pXO2 plasmids leads to the repression of 14 chromosomal genes. On the other hand, in minimal aerobic medium not supplemented with CO(2), the virulent and avirulent B. anthracis strains manifest very similar protein signatures, and most strikingly, two proteins (the metalloproteases InhA1 and NprB, orthologs of gene products attributed to the Bacillus cereus group PlcR regulon) represent over 90% of the total secretome. Interestingly, of the 64 identified gene products, at least 31 harbor features characteristic of virulence determinants (such as toxins, proteases, nucleotidases, sulfatases, transporters, and detoxification factors), 22 of which are differentially regulated in a plasmid-dependent manner. The nature and the expression patterns of proteins in the various secretomes suggest that distinct CO(2)-responsive chromosome- and plasmid-encoded regulatory factors modulate the secretion of potential novel virulence factors, most of which are associated with extracellular proteolytic activities.     

蜡状芽胞杆菌群菌株中部分病原相关因子的检测

对26株蜡状芽胞杆菌群菌株进行了肠毒素基因及其它病原相关因子的检测。PCR结果表明,17株蜡状芽胞杆菌群菌株中含有病原调控因子plcR的同源序列。采用3组溶血肠毒素hbl基因和3组非溶血肠毒素nhe基因特异性引物,分别可从73%的菌株中至少扩增出一个与预期DNA片段大小一致的片段,其中,苏云金芽胞杆菌菌株中溶血素hbl基因和非溶血素nhe基因的阳性检出率为83%。蜡状芽胞杆菌DBt248完全没有溶血活性,而且在溶血素hbl和非溶血素nhe基因的3个亚基以及病原调控因子plcR的PCR检测中均为阴性,有望作为宿主菌用于苏云金芽胞杆菌晶体蛋白的表达和应用。     

Adhesion and cytotoxicity of Bacillus cereus and Bacillus thuringiensis to epithelial cells are FlhA and PlcR dependent, respectively

Some bacteria of the Bacillus cereus group are enteropathogens. The first cells encountered by bacteria following oral contamination of the host are epithelial cells. We studied the capacity of these bacteria to adhere to epithelial cells and the consequences of this interaction. We found that cell adhesion is strain dependent and that a strain mutated in flhA, which encodes a component of flagellum-apparatus formation, is impaired in adhesion, suggesting that flagella are important virulence factors. The bacteria are cytotoxic to epithelial cells and induce substantial cytoplasmic and membrane alterations. However, direct contact between cells and bacteria is not required for cytotoxicity. The determinants of this cytotoxicity are secreted and their expression depends on the pleiotropic regulator PlcR. Adhesion and cytotoxicity of B. cereus to epithelial cells might explain the diarrhea caused by these pathogens. Our findings provide further insight into the pathogenicity of B. cereus group members.