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

Abstract

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.

The plcR regulon is involved in the opportunistic properties of Bacillus thuringiensis and Bacillus cereus in mice and insects

“…This is consistent with the taxonomic identity of B. thuringiensis and B. cereus (Carlson & Kolstø, 1993 ;Helgason et al, 2000). The two species have extensive genome identity, including a complete copy of the plcR gene (Agaisse et al, 1999 ;.…”

“…PlcR-regulated genes encode proteins containing sequences similar to secretory signal peptides (Agaisse et al, 1999 ;. Thus, the 407 Cry − ∆plcR strain may be less able to cause opportunistic infections due to its inability to produce one or several of these secreted factors.…”

“…Two phosphatidylcholine esterases are known to be encoded by PlcRregulated genes (Agaisse et al, 1999). They are phospholipase C and sphingomyelinase, which together form cereolysin AB (Gilmore et al, 1989).…”

“…A transcriptional activator that positively regulates the expression of phospholipase C genes, during the late vegetative growth of B. thuringiensis cells, has been identified and named PlcR (Lereclus et al, 1996). This regulator governs the expression of a large regulon encoding extracellular proteins including degradative enzymes, cell-surface proteins and enterotoxins (Agaisse et al, 1999). Hence, PlcR appears to be a pleiotropic regulator of genes encoding extracellular factors potentially involved in pathogenicity.…”

Bacterial endophthalmitis: Therapeutic challenges and host–pathogen interactions

“…However, endophthalmitis can also be caused by Bacillus thuringiensis, a bacterium commonly used for organic gardening and farming that is genetically and phenotypically similar to B. cereus (Callegan, et al, 2006a). For B. cereus and B. thuringiensis, the quorum sensing transcriptional regulator plcR controls the expression of many extracellular virulence factors (Agaisse, et al, 1999). In an experimental rabbit model of endophthalmitis, B. cereus and B. thuringiensis were significantly less virulent when plcR was nonfunctional (Callegan, et al, 2003 Conf., 2005).…”