DNA sequence conservation between the Bacillus anthracis pXO2 plasmid and genomic sequence from closely related bacteria

Abstract

Background: Complete sequencing and annotation of the 96.2 kb Bacillus anthracis plasmid, pXO2, predicted 85 open reading frames (ORFs). Bacillus cereus and Bacillus thuringiensis isolates that ranged in genomic similarity to B. anthracis, as determined by amplified fragment length polymorphism (AFLP) analysis, were examined by PCR for the presence of sequences similar to 47 pXO2 ORFs.

Results: The two most distantly related isolates examined, B. thuringiensis 33679 and B. thuringiensis AWO6, produced the greatest number of ORF sequences similar to pXO2; 10 detected in 33679 and 16 in AWO6. No more than two of the pXO2 ORFs were detected in any one of the remaining isolates. Dot-blot DNA hybridizations between pXO2 ORF fragments and total genomic DNA from AWO6 were consistent with the PCR assay results for this isolate and also revealed nine additional ORFs shared between these two bacteria. Sequences similar to the B. anthracis cap genes or their regulator, acpA, were not detected among any of the examined isolates.

Conclusions: The presence of pXO2 sequences in the other Bacillus isolates did not correlate with genomic relatedness established by AFLP analysis. The presence of pXO2 ORF sequences in other Bacillus species suggests the possibility that certain pXO2 plasmid gene functions may also be present in other closely related bacteria.

Figure 1

Pulsed field gel electrophoresis of DNA from B. thuringiensis AWO6. Panel A, Ethidium bromide-stained agarose gel. Lane 1 is the PFGE DNA size marker. Lane 2 is B. thuringiensis AWO6 DNA. Lane 3 is a Southern blot of pXO2-derived probes hybridizing to a DNA band the size of the pAW63 plasmid. Panel B, size of pAW63 plasmid and hybridizing DNA determined using PFGE.