Bacillus sphaericus as a Mosquito Pathogen : Properties of the Organism and Its Toxinst PAUL BAUMANN , ' * MARTA

In the course of sporulation, some strains of Bacillus sphaericus synthesize a parasporal inclusion or "crystal" (Fig. 1), which contains proteins toxic for larvae of a variety of mosquito species (64, 74). Upon completion of sporulation, the crystal remains associated with the endospore, both being enclosed within the exosporium (74). The major components of the crystal are two proteins of 51 and 42 kDa (12); neither protein alone is toxic to larvae, and both are required for toxicity (11, 20, 23). Following ingestion of the crystal by mosquito larvae, these two proteins are solubilized in the midgut (19, 74). Electron-microscopic studies have indicated the midgut epithelial cells as the primary target of the toxin (24, 74). B. sphaericus has been successfully used for the biological control of mosquito species which are vectors of important human diseases (56, 74). A number of other bacilli resemble B. sphaericus in producing parasporal crystals (6). The most extensively studied species is Bacillus thuringiensis (6, 52, 72). Members