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BMC Genomics  2006 

Molecular characterization of a DNA fragment harboring the replicon of pBMB165 from Bacillus thuringiensis subsp. tenebrionis

DOI: 10.1186/1471-2164-7-270

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Abstract:

A 20 kb DNA fragment containing a plasmid replicon was isolated from B. thuringiensis subsp. tenebrionis YBT-1765 and characterized. By Southern blot analysis, this replicon region was determined to be located on pBMB165, the largest detected plasmid (about 82 kb) of strain YBT-1765. Deletion analysis revealed that a replication initiation protein (Rep165), an origin of replication (ori165) and an iteron region were required for replication. In addition, two overlapping ORFs (orf6 and orf10) were found to be involved in stability control of plasmid. Sequence comparison showed that the replicon of pBMB165 was homologous to the pAMβ1 family replicons, indicating that the pBMB165 replicon belongs to this family. The presence of five transposable elements or remnants thereof in close proximity to and within the replicon control region led us to speculate that genetic exchange and recombination are potentially responsible for the divergence among the replicons of this plasmid family.The replication and stability features of the pBMB165 from B. thuringiensis subsp. tenebrionis YBT-1765 were identified. Of particular interest is the homology and divergence shared between the pBMB165 replicon and other pAMβ1 family replicons.B. thuringiensis, belonging to the Bacillus cereus sensu lato group, is a gram-positive and spore-forming bacterium that produces parasporal crystals during sporulation. The proteinaceous parasporal crystals show toxicity against insect larvae. The toxin protein genes, usually insecticidal crystal protein (ICP) genes, are mainly located on large conjugative plasmids [1].B. thuringiensis strains appear to contain plasmid DNA in proportion of 10–20% of total cell DNA [2]. Generally, plasmids of different B. thuringiensis strains vary in number and size, with the number between 1–12 and the size from 2 to > 250 kb [3,4]. In addition to harboring ICP genes, B. thuringiensis plasmids can also bear insertion sequences and transposons that are commonly associa

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