BMC Genomics Research article Conjugative plasmid pAW63 brings new insights into the genesis of the Bacillus anthracis virulence plasmid pXO2 and of the Bacillus thuringiensis plasmid pBT9727 Géraldine A Van der Auwera1, Lars Andrup2 and Jacques Mahillon*1 BioMed Central Open Access Address: 1Laboratory of Food and Environmental Microbiology, Université catholique de Louvain, Croix du Sud 2/12, B-1348 Louvain-la-Neuve, Belgium and 2National Institute of Occupational Health, Lersø Parkallé 105, DK-2100 Copenhagen, Denmark Email: Géraldine A Van der Auwera - vanderauwera@mbla.ucl.ac.be; Lars Andrup - la@ami.dk; Jacques Mahillon* - mahillon@mbla.ucl.ac.be * Corresponding author Published: 26 July 2005 BMC Genomics 2005, 6:103 doi:10.1186/1471-2164-6-103 This article is available from: http://www.biomedcentral.com/1471-2164/6/103 Received: 09 May 2005 Accepted: 26 July 2005 © 2005 Van der Auwera et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract Background: Bacillus cereus, Bacillus anthracis and Bacillus thuringiensis belong to the genetically close-knit Bacillus cereus sensu lato group, a family of rod-shaped Gram-positive bacteria. pAW63 is the first conjugative plasmid from the B. cereus group to be completely sequenced. Results: The 71,777 bp nucleotide sequence of pAW63 reveals a modular structure, including a 42 kb tra region encoding homologs of the Type IV secretion systems components VirB11, VirB4 and VirD4, as well as homologs of Gram-positive conjugation genes from Enterococcus, Lactococcus, Listeria, Streptococcus and Staphylococcus species. It also firmly establishes the existence of a common backbone between pAW63, pXO2 from Bacillus anthracis and pBT9727 from the pathogenic Bacillus thuringiensis serovar konkukian strain 97-27. The alignment of these three plasmids highlights the presence of well conserved segments, in contrast to distinct regions of high sequence plasticity. The study of their specific differences has provided a three-point reference framework that can be exploited to formulate solid hypotheses concerning the functionalities and the molecular evolution of these three closely related plasmids. This has provided insight into the chronology of their divergence, and led to the discovery of two Type II introns on pAW63, matching copies of the mobile element IS231L in different loci of pXO2 and pBT9727, and the identification on pXO2 of a 37 kb pathogenicity island (PAI) containing the anthrax capsule genes. Conclusion: The complete sequence determination of pAW63 has led to a functional map of the plasmid yielding insights into its conjugative apparatus, which includes T4SS-like components, as well as its resemblance to other large plasmids of Gram-positive bacteria. Of particular interest is the extensive homology shared between pAW63 and pXO2, the second virulence plasmid of B. anthracis, as well as pBT9727 from the pathogenic strain B. thuringiensis serovar konkukian strain 97- 27. Background The Bacillus cereus sensu lato family of rod-shaped Gram- positive bacteria contains six subspecies that are geneti- cally very close [1] but nonetheless have highly special- ized lifestyles, especially as concerns their respective virulence spectra. Most notable are B. cereus sensu stricto, Page 1 of 14 (page number not for citation purposes)