Temperature Dependent Toxin Expression in Bacillus Cereus G9241, the Causative Agent of Anthrax like Illness

Bacillus cereus G9241, a member of the Bacillus cereus sensu lato complex, was isolated from a Louisiana welder with a pulmonary anthrax-like illness and is closely related to B. anthracis. Most members of the B. cereus group express PlcR, a pleiotropic transcriptional regulator of secreted toxins and enzymes allowing insect infection, which is activated by the peptide PapR at stationary phase of growth. However, in all B. anthracis isolates, the plcR gene contains a point mutation, which frame-shifts the gene, thus inactivating it. It has been proposed that the acquisition of AtxA, the mammalian responsive transcriptional regulator, was incompatible with the activity of PlcR, leading to selection for PlcR inactivation. Interestingly, G9241 encodes intact copies of both atxA and plcR. Preliminary data has shown that B. cereus G9241 has a temperature dependent haemolytic activity, possibly caused by haemolysins that are regulated by PlcR. We hypothesise that a change in the PlcR-PapR regulatory network in G9241 has allowed the co-existence of plcR and atxA through temperature dependent suppression of the PlcR-PapR circuit at the time AtxA becomes active.Here we investigated whether the activity of the PlcR-PapR circuit and PlcR regulated toxins in B. cereus G9241 are temperature dependent (25 °C and 37 °C), in order to accommodate the activity of AtxA. Plasmid based transcription-translation GFP reporter of PlcR, PapR and PlcR-regulated toxins have been used to study translational activity.