B. thuringiensis DB27 (BT DB27) kills diverse nematodes via intestinal infection. (A) C. elegans survival on monoxenic cultures of B. thuringiensis DB27. Pure spores of B. thuringiensis DB27 are significantly (P < 0.0001) more toxic to C. elegans than a mixture of spores and vegetative cells. Vegetative (veg) cells alone are not virulent. (B) B. thuringiensis DB27 did not repel C. elegans in a chemotaxis assay, in contrast to Serratia marcescens, used as a positive control. (C) C. elegans survival after a short exposure to B. thuringiensis DB27 (pulse-chase). The x axis shows the pulse (time of exposure to the pathogen). The y axis shows the number of nematodes (scored 24 h postinfection) that recovered after a given pulse. (D to F) C. elegans intestinal changes caused by B. thuringiensis DB27. Compared to control worms on OP50 (D), worms exposed to B. thuringiensis DB27 exhibit intestinal shrinkage (E) and accumulation of bacteria in the gut (F). Bar, 20 μm. (G to I) Other nematodes show levels of susceptibility that differ from that of B. thuringiensis DB27. (G) O. carolinensis and P. strongyloides are more resistant (P < 0.0001) to B. thuringiensis DB27-mediated killing than C. elegans. (H) P. redivivus is significantly (P < 0.001) more susceptible than C. elegans. (I) Animal-parasitic nematode S. papillosus is killed rapidly by B. thuringiensis DB27 compared to control E. coli OP50. For survival curves, the number of worms alive (N nematodes) is plotted as a function of time. The data shown are means ± standard errors of the means.