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 B. anthracis pXO1

David A. Rasko^*, M. J. Rosovitz, Ole Andreas kstad, Derrick E. Fouts, Lingxia Jiang, Regina Z. Cer, Anne-Brit Kolstø, Steven R. Gill, and Jacques Ravel

Biotechnology Center of Oslo, University of Oslo, PB1125 Blindern, 0316 Oslo, Norway, Department of Pharmaceutical Biosciences, University of Oslo, PB1068 Blindern, 0316 Oslo, Norway, The Institute for Genomic Research, 9712 Medical Center Drive, Rockville MD 20850

^* To whom correspondence should be addressed. Email: david.rasko{at}utsouthwestern.edu,

	Abstract

The plasmids of the members of the Bacillus cereus sensu lato group of organisms are essential in defining the phenotypic traits associated with pathogenesis and ecology. For example, Bacillus anthracis contains 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 defines Bacillus thuringiensis isolates. In this study the plasmids from B. cereus isolates 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 these B. cereus plasmids revealed a high degree of sequence similarity to the B. anthracis pXO1 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 identified B. cereus plasmids. Screening of a population of B. cereus group isolates revealed that pXO1-like plasmids are more often found in association with clinical isolates. This work demonstrates that the pXO1-like plasmids may define pathogenic B. cereus isolates in the same way that pXO1 and pXO2 define the B. anthracis species.