Bacillus anthracisVirulent Plasmid pX02 Genes Found in Large Plasmids of Two Other BacillusSpecies

ABSTRACTIn order to cause the disease anthrax, Bacillus anthracisrequires two plasmids, pX01 and pX02, which carry toxin and capsule genes, respectively, that are used as genetic targets in the laboratory detection of the bacterium. Clinical, forensic, and environmental samples that test positive by PCR protocols established by the Centers for Disease Control and Prevention for B. anthracisare considered to be potentially B. anthracisuntil confirmed by culture and a secondary battery of tests. We report the presence of 10 genes (acpA, capA, capB, capC, capR, capD, IS1627, ORF 48, ORF 61, and repA) and the sequence for the capsule promoter normally found on pX02 in Bacillus circulansand a Bacillusspecies closely related to Bacillus luciferensis. Tests revealed these sequences to be present on a large plasmid in each isolate. The 11 sequences consistently matched to B. anthracisplasmid pX02, GenBank accession numbers AF188935.1, AE011191.1, and AE017335.3. The percent nucleotide identities for capDand the capsule promoter were 99.9% and 99.7%, respectively, and for the remaining nine genes, the nucleotide identity was 100% for both isolates. The presence of these genes, which are usually associated with the pX02 plasmid, in two soil Bacillusspecies unrelated to B. anthracisalerts us to the necessity of identifying additional sequences that will signal the presence of B. anthracisin clinical, forensic, and environmental samples.