The three Bacillus anthracis toxin genes are coordinately regulated by bicarbonate and temperature.

The two Bacillus anthracis toxins are composed of three proteins, protective antigen, lethal factor, and edema factor. The structural genes for these three components are located on the virulence plasmid pXO1. We constructed transcriptional fusions between the regulatory region of each of these genes and lacZ. Each construct was then inserted as a single copy at the corresponding toxin gene locus on pXO1, resulting in three isogenic strains. Two environmental factors, bicarbonate and temperature, were found to induce beta-galactosidase synthesis in each recombinant strain. Furthermore, the transcription of the three toxin genes appears to be coordinately regulated.