Cloning and expression of the Bacillus anthracis protective antigen gene in Bacillus subtilis

The gene encoding the protective antigen (PA) moiety of the tripartite exotoxin of Bacillus anthracis was cloned from the recombinant plasmid pSE36 into Bacillus subtilis 1S53 by using the plasmid vector pUB110. Two clones, designated PA1 and PA2, were identified which produced PA in liquid cultures at levels of 20.5 to 41.9 micrograms/ml. This PA was identical to B. anthracis Sterne PA with respect to migration on sodium dodecyl sulfate-polyacrylamide gels and to Western blot antigenic reactivity. Addition of lethal factor or edema factor to PA1 and PA2 supernatants generated biologically active anthrax lethal toxin or edema-producing toxin, respectively. The recombinant plasmid in PA1 (pPA101) was 7.8 kilobases, whereas the PA2 strain plasmid (pPA102) was 6.1 kilobases. Both plasmids had deletions extending into the insert sequence but not into the DNA encoding the PA protein. Immunization with the live recombinant strains protected guinea pigs from lethal challenge with virulent B. anthracis spores, and the immunization partially or completely protected rats from intravenous challenge with anthrax lethal toxin.