FIG 3.

Cry21 protoxins are the nematicidal virulence factors of B. thuringiensis DB27. (A) C. elegans survival on E. coli which expresses individual Cry21 protoxins. Cry21Fa1 and Cry21Ha1 significantly (P < 0.0001) reduce C. elegans survival compared to the vector control. The Cry21Ga1 effect is similar (P > 0.05) to that of the vector control. (B and C) C. elegans fed with E. coli-expressed Cry21Fa1 protoxin exhibits dramatic intestinal shrinkage and destruction (C) compared to vector-fed control worms (B). Bars, 100 μm. (D) C. elegans survival upon exposure to combinations of E. coli clones that express different Cry21 protoxins. C. elegans survival is significantly (P < 0.0001) reduced when worms are exposed to the combination of Cry21Fa1 and Cry21Ha1 protoxins compared to exposure to each toxin individually. Combining Cry21Ga1 with either Cry21Fa1 or Cry21Ha1 does not significantly (P > 0.05) change the survival compared to that seen with the individual protoxins. The combination of all three proteins is almost as toxic as the combination of Cry21Fa1 and Cry21Ha1, suggesting that Cry21Ga1 has no synergistic effect. (E) The nasp-1 mutant is significantly more resistant to Cry21Fa1 (P < 0.0001) and Cry21Ha1 (P < 0.001) protoxins than the wild-type strain. The data shown are means ± standard errors of the means. (F and G) C. elegans dose-dependent lethality to purified Cry21Fa1 (F) and Cry21Ha1 (G) protoxins in a liquid assay. A semilog plot of animals that died versus the concentration of toxin is shown. The data were fitted to a line by the least-squares method. The LC₅₀s for Cry21Fa1 (13.6 μg/ml) and for Cry21Ha1 (23.9 μg/ml) were calculated from the line fits. The data can be found in Materials and Methods.