Parasporal crystals produced by oligosporogenous mutans of Bacillus thuringiensis (Spo-Cr+).

Six oligosporogenic (Spo-) mutant strains of Bacillus thuringiensis were selected from survivors of treatment with N-methyl-N'-nitro-N-nitrosoguanidine. Each strain was blocked at or before stage II of spore development, but all produced typical bipyramidal-shaped crystalline inclusion bodies. Toxicity of the paraporad typical bipyramidal-shaped crystalline inclusion bodies. Toxicity of the parasporal endotoxin isolated from the mutant strains was assayed by an in vitro technique using cultured insect cells, and was comparable with that of normal wild-type parasporal protein. Multiple parasporal inclusion bodies per cell were often produced, and smaller embedded particles were numerous and distinct.