PlcR is a pleiotropic regulator of extracellular virulence factor gene expression in Bacillus thuringiensis

Members of the Bacillus cereus group (B. anthracis, B. cereus, B. mycoides and B. thuringiensis) are well-known pathogens of mammals (B. anthracis and B. cereus) and insects (B. thuringiensis), The specific diseases they caus e depend on their capacity to produce specific virulence factors, such as t he lethal toxin of B. anthracis and the Cry toxins of B. thuringiensis. How ever, these Bacillus spp. also produce a variety of proteins, such as phosp holipases C, which are known to act as virulence factors in various pathoge nic bacteria. Few genes encoding these virulence factors have been characte rized in pathogenic Bacillus spp. and little is known about the regulation of their expression. We had previously reported that in B. thuringiensis ex pression of the phosphatidylinositol-specific phospholipase C gene is regul ated by the transcriptional activator PlcR. Here we report the identificati on of several extracellular virulence factor genes by the virtue of their P lcR-regulated expression. These PlcR-regulated genes encode degradative enz ymes, cell-surface proteins and enterotoxins. The PlcR-regulated genes are widely dispersed on the chromosome and therefore do not constitute a pathog enic island. Analysis of the promoter region of the PlcR-regulated genes re vealed the presence of a highly conserved palindromic region (TATGNAN(4)TNC ATA), which is presumably the specific recognition target for PlcR activati on. We found that the plcR gene is also present in and probably restricted to all the members of the B. cereus group. However,;although the polypeptid e encoded by the B, cereus plcR gene is functionally equivalent to the a. t huringiensis regulator, the polypeptide encoded by the B. anthracis gene is truncated and not active as a transcriptional activator. PlcR is the first example described of a pleiotropic regulator involved in the control of ex tracellular virulence factor expression in pathogenic Bacillus spp. These r esults have implications for the taxonomic relationships among members of t he B. cereus group, the virulence properties of these bacteria and the safe ty of B. thuringiensis-based biopesticides.