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 cause depend 
on their capacity to produce specific virulence factors, such as the lethal 
toxin of B. anthracis and the Cry toxins of B. thuringiensis. However, these 
Bacillus spp. also produce a variety of proteins, such as phospholipases C, 
which are known to act as virulence factors in various pathogenic bacteria. Few 
genes encoding these virulence factors have been characterized in pathogenic 
Bacillus spp. and little is known about the regulation of their expression. We 
had previously reported that in B. thuringiensis expression of the 
phosphatidylinositol-specific phospholipase C gene is regulated by the 
transcriptional activator PlcR. Here we report the identification of several 
extracellular virulence factor genes by the virtue of their PlcR-regulated 
expression. These PlcR-regulated genes encode degradative enzymes, cell-surface 
proteins and enterotoxins. The PlcR-regulated genes are widely dispersed on the 
chromosome and therefore do not constitute a pathogenic island. Analysis of the 
promoter region of the PlcR-regulated genes revealed the presence of a highly 
conserved palindromic region (TATGNAN4TNCATA), which is presumably the specific 
recognition target for PlcR activation. 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 polypeptide encoded by the B. cereus PlcR gene is 
functionally equivalent to the B. thuringiensis 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 extracellular virulence factor expression 
in pathogenic Bacillus spp. These results have implications for the taxonomic 
relationships among members of the B. cereus group, the virulence properties of 
these bacteria and the safety of B. thuringiensis-based biopesticides.