Complete nucleotide sequence of pBMB67, a 67-kb plasmid from Bacillus thuringiensis strain YBT-1520

The complete nucleotide sequence of a large (67kb) cryptic plasmid pBMB67 from Bacillus thuringiensis strain YBT-1520 was determined. Of the 74 predicted open reading frames (ORFs), 25 (34%) were assigned putative functions, 18 (24%) encoded conserved hypothetical proteins, and 31 (42%) had no homology to any genes present in the current open databases. The ORFs with similar functions were organized in a modular structure; thus, the DNA sequence of pBMB67 could be functionally divided into three modules, including a 39kb transfer region encoding homologs of the Agrobacterium tumefaciens VirB/D4 system components VirB1, VirB4, VirB11, and VirD4, as well as homologs of Gram-positive conjugation proteins. We also found a potential operon that was analogous to the Rap-Phr cassettes from Bacillus subtilis, which are involved in cell-cell communication and transcriptional regulation. Thus, we suggest that pBMB67 is likely to be implicated in cell-cell signaling and plays a role in the regulation of several cellular processes, with the production of exoprotease being one of the candidates.