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Journal of Bacteriology, November 2004, p. 7714-7725, Vol. 186, No. 22
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.22.7714-7725.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

The bcr1 DNA Repeat Element Is Specific to the Bacillus cereus Group and Exhibits Mobile Element Characteristics

Ole Andreas Økstad,^1,2, Nicolas J. Tourasse,^1, Fredrik B. Stabell,¹ Cathrine K. Sundfær,¹ Wolfgang Egge-Jacobsen,¹ Per Arne Risøen,² Timothy D. Read,^3, and Anne-Brit Kolstø^1,2*

Biotechnology Centre of Oslo,¹ School of Pharmacy, University of Oslo, Oslo, Norway,² The Institute for Genomic Research, Rockville, Maryland³

Received 6 April 2004/ Accepted 7 July 2004

Bacillus cereus strains ATCC 10987 and ATCC 14579 harbor a 155-bp repeated element, bcr1, which is conserved in B. cereus, B. anthracis, B. thuringiensis, and B. mycoides but not in B. subtilis and B. licheniformis. In this study, we show by Southern blot hybridizations that bcr1 is present in all 54 B. cereus group strains tested but absent in 11 Bacillus strains outside the group, suggesting that bcr1 may be specific and ubiquitous to the B. cereus group. By comparative analysis of the complete genome sequences of B. cereus ATCC 10987, B. cereus ATCC 14579, and B. anthracis Ames, we show that bcr1 is exclusively present in the chromosome but absent from large plasmids carried by these strains and that the numbers of full-length bcr1 repeats for these strains are 79, 54, and 12, respectively. Numerous copies of partial bcr1 elements are also present in the three genomes (91, 128, and 53, respectively). Furthermore, the genomic localization of bcr1 is not conserved between strains with respect to chromosomal position or organization of gene neighbors, as only six full-length bcr1 loci are common to at least two of the three strains. However, the intergenic sequence surrounding a specific bcr1 repeat in one of the three strains is generally strongly conserved in the other two, even in loci where bcr1 is found exclusively in one strain. This finding indicates that bcr1 either has evolved by differential deletion from a very high number of repeats in a common ancestor to the B. cereus group or is moving around the chromosome. The identification of bcr1 repeats interrupting genes in B. cereus ATCC 10987 and ATCC 14579 and the presence of a flanking TTTAT motif in each end show that bcr1 exhibits features characteristic of a mobile element.

O.A.Ø. and N.J.T. contributed equally to the study.

Present address: Biological Defense Research Directorate, Naval Medical Research Center, Silver Spring, MD 20910.

This article has been cited by other articles:

• Klevan, A., Tourasse, N. J., Stabell, F. B., Kolsto, A.-B., Okstad, O. A. (2007). Exploring the evolution of the Bacillus cereus group repeat element bcr1 by comparative genome analysis of closely related strains. Microbiology 153: 3894-3908 [Abstract] [Full Text]