FIG 2.

B. thuringiensis DB27 virulence factors are plasmid-associated Cry protoxins. (A) Plasmid profile of B. thuringiensis DB27 (lanes 1 and 2) and its plasmid-cured derivative (lanes 3 and 4). B. thuringiensis DB27 has seven plasmids (marked with dots), while the plasmid-cured variant lost all of them. M, marker (kb). Considering that the marker is represented by linear DNA fragments and the state of the plasmids (linear, circular, or supercoiled) is not known, it cannot be used as a determinant of the exact plasmid size. (B) C. elegans survival on the B. thuringiensis DB27 plasmid-cured variant is not affected (P < 0.0001) compared to that of the wild-type (wt) strain. (C and D) Light microscopy images (100×) of Coomassie-stained spore-crystal mixtures of wild-type B. thuringiensis DB27 (C) and its plasmidless derivative (D). Crystals (stained in black in panel C) show a strong association with the spore (SCA phenotype). No crystal inclusions are formed by plasmid-cured derivative. Rod-like black structures not attached to spores are vegetative cells. Bars, 100 μm. (E and F) Scanning electron microscopy images of spore-crystal mixtures of wild-type B. thuringiensis DB27 (E) and its plasmidless derivative (F). Arrows point to spores (S), crystals (C), and vegetative cells (V).