Complete sequence and organization of pBtoxis, the toxin-coding plasmid of Bacillus thuringiensis subsp. israelensis

Abstract

The entire 127,923-bp sequence of the toxin-encoding plasmid pBtoxis from Bacillus thuringiensis subsp. israelensis is presented and analyzed. In addition to the four known Cry and two known Cyt toxins, a third Cyt-type sequence was found with an additional C-terminal domain previously unseen in such proteins. Many plasmid-encoded genes could be involved in several functions other than toxin production. The most striking of these are several genes potentially affecting host sporulation and germination and a set of genes for the production and export of a peptide antibiotic.

FIG. 1.

Circular representation of pBtoxis. The inner circle represents GC bias [(G − C)/(G + C)], with positive values in khaki and negative values in purple; the second circle represents G+C content; and the outer two circles represent predicted genes on the reverse and forward strands (selected CDSs are numbered for reference). Color coding for the genes is as follows: gray, toxin and peptide antibiotic; pink, transposon related; orange, conserved hypothetical; red, DNA metabolism; blue, regulatory; bright green, surface associated; pale green, unknown; yellow, miscellaneous metabolic genes. The outer scale is marked in kilobases.

FIG. 2.

Linear representation of the pBtoxis-pXO1 comparison. pBtoxis is shown above, and pXO1 is below. GC bias [(G − C)/(G + C)] plots are shown for each plasmid, and the putative origin is indicated. Protein-protein similarities (as determined by TBLASTX comparisons of the complete plasmids) are indicated in the center, with the strength of the match indicated by the intensity of the red color. The color coding for pBtoxis genes is as in Fig. 1, except that the toxin and peptide antibiotic genes are in white. The pXO1 pathogenicity island (PAI) containing the toxin genes is marked with a horizontal line, and the transposon-related genes in each plasmid are indicated with black triangles; selected pBtoxis CDSs are labeled. The representation was drawn with ACT (http://www.sanger.ac.uk/Software/ACT), which can be used to visualize the complete comparison interactively.