Complete Sequence Analysis of Novel Plasmids from Emetic and Periodontal Bacillus cereus Isolates Reveals a Common Evolutionary History among the B. cereus -Group Plasmids, Including Bacillus anthracis pXO1

Abstract

The plasmids of the members of theBacillus cereussensu lato group of organisms are essential in defining the phenotypic traits associated with pathogenesis and ecology. For example,Bacillus anthraciscontains two plasmids, pXO1 and pXO2, encoding toxin production and encapsulation, respectively, that define this species pathogenic potential, whereas the presence of a Bt toxin-encoding plasmid definesBacillus thuringiensisisolates. In this study the plasmids fromB. cereusisolates that produce emetic toxin or are linked to periodontal disease were sequenced and analyzed. Two periodontal isolates examined contained almost identical ∼272-kb plasmids, named pPER272. The emetic toxin-producing isolate contained one ∼270-kb plasmid, named pCER270, encoding the cereulide biosynthesis gene cluster. Comparative sequence analyses of theseB. cereusplasmids revealed a high degree of sequence similarity to theB. anthracispXO1 plasmid, especially in a putative replication region. These plasmids form a newly defined group of pXO1-like plasmids. However, these novel plasmids do not contain the pXO1 pathogenicity island, which in each instance is replaced by plasmid specific DNA. Plasmids pCER270 and pPER272 share regions that are not found in any other pXO1-like plasmids. Evolutionary studies suggest that these plasmids are more closely related to each other than to other identifiedB. cereusplasmids. Screening of a population ofB. cereusgroup isolates revealed that pXO1-like plasmids are more often found in association with clinical isolates. This study demonstrates that the pXO1-like plasmids may define pathogenicB. cereusisolates in the same way that pXO1 and pXO2 define theB. anthracisspecies.

Biochemical and molecular characterization of Bacillus pumilus isolated from coastal environment in Cochin, India

“…Cereulide is a small heat stable cyclic dodecadepsipeptide produced by some strains of B. cereus which has high toxicity to humans (1,36). Cereulide is synthesized by a non-ribosomal peptide synthetase, encoded by the ces genes located on a 270-kb pXOI-like virulence plasmid named pCER270 (10,26), more often found associated with clinical isolates of B. cereus. A recent study has reported the presence of cesA, but not cesB, in B. pumilus and B. licheniformis isolated from bovine mastitis (20).…”

“…2). The product of cesB PCR was sequenced and nucleotide sequence analysis of the PCR product revealed (26), while the deduced amino acid sequence showed 92% homology with a few amino acid mismatches (Fig. 3).…”

Genomic characterization of theBacillus cereussensu lato species: Backdrop to the evolution ofBacillus anthracis

“…Despite the multiple species names, which are often attributed to phenotypes conferred by mobile genetic elements, all these organisms can be considered members of a single species, because of their low genetic diversity, as measured by 16S sequencing (Daffonchio et al 2003) and multilocus sequence typing (MLST) (Priest et al 2004), and their high degree of shared gene content (Rasko et al 2005). Aside from B. anthracis, other reported virulent strains include a small number of nontraditional anthrax isolates (Hoffmaster et al 2004;Klee et al 2010), bacteria that cause wound or soft-tissue infections, a clonal complex of emetic toxin producers (Rasko et al 2007), and isolates responsible for food poisoning. Most B. cereus s.l.…”

pXO1-and pXO2-like Plasmids in Bacillus cereus and B. thuringiensis

“…The emetic toxin-producing isolate contained one 270-kb plasmid, named pCER270, encoding the cereulide biosynthesis gene cluster. Comparative sequence analyses of these B.cereus plasmids revealed a high degree of sequence similarity to the B. anthracis pXO1 plasmid, especially in a putative replication region (4).…”

“…Numerous studies have attempted to characterize the role of these plasmids in virulence. Generating a plasmid-free strain is important to elucidate the crosstalk between the plasmids and host chromosome (3,4).…”