Sequence analysis of three Bacillus cereus loci carrying PlcR-regulated genes encoding degradative enzymes and enterotoxin

PlcR is a pleiotropic regulator of extracellular virulence factors in the o pportunistic human pathogen Bacillus cereus and the entomopathogenic Bacill us thuringiensis, and is induced in cells entering stationary phase. Among the genes regulated by PlcR are: PICA, encoding phosphatidylinositol-specif ic phospholipase C (PI-PLC); pie, encoding phosphatidylcholine-preferring p hospholipase C (PC-PLC); nhe, encoding the non-haemolytic enterotoxin; hbl, encoding haemolytic enterotoxin BL (HBL); and genes specifying a putative S-layer like surface protein and a putative extracellular RNase, By analysi ng 37.1 kb of DNA sequence surrounding hbl, PlcA and PlcR, 28 ORFs were pre dicted. Three novel genes putatively regulated by PlcR and encoding a neutr al protease (NprB), a subtilase family serine protease (Sfp) and a putative cell-wail hydrolase (Cwh) were identified, The corresponding sfP and Cwh g enes were located in the immediate upstream region of PICA and could both b e regulated by a putative PlcR-binding site positioned between the inversel y transcribed genes. Similarly, nprB was positioned directly upstream and t ranscribed in the opposite orientation to PlcR, Genes surrounding PlcA, Plc R and hblCDAB that were lacking an upstream PlcR regulatory sequence did no t appear to serve functions apparently related to PlcR and did not exhibit a conserved organization in Bacillus subtilis.